Chapter 9

Diesels For Dummies

In This Chapter

Weighing the advantages and disadvantages of diesel-powered vehicles

Exploring diesel fuel, electrical, and exhaust systems

Troubleshooting and maintaining diesel engines

Starting a diesel when it’s cold outside

Identifying a good diesel mechanic

Think of this chapter as a mini-version of Auto Repair For Dummies devoted entirely to diesel-powered vehicles. It explores the new generation of clean diesel vehicles and explains how diesel engines work. It also provides instruc-tions for maintaining and troubleshooting diesel-powered vehicles and for finding a good diesel mechanic when your best efforts just aren’t enough.

Whenever you encounter a term set in this font, you’ll find it defined in the glossary in Appendix A.

Clean Diesels: Nontoxic Newcomers

Diesel-powered vehicles are popular in the large part of the world where gasoline is very expensive or almost unavailable. In the United States and Canada, up until recently diesel engines were found mainly in heavy equipment, large trucks, buses, heavy-duty pickup trucks, and boats. Diesel- powered passenger vehicles existed, but they had a reputation for being noisy, underpowered, smelly, and carcinogenic. For a short period in the 1980s people overlooked those negatives when fuel shortages made diesel-powered vehicles popular because they got 25 percent more miles per gallon than gasoline engines and diesel fuel was less expensive than gasoline. They soon fell out of favor because major carmakers dropped diesel engines into vehicles that weren’t equipped to withstand the higher stress these engines imposed.

The good news is that growing concern about the environment and the disturbing news that emissions from high-sulfur diesel oil were contributing not only to air pollution and global warming but to cancer as well produced legislation that accelerated technological breakthroughs in diesel mechanics. The result is a new generation of clean diesel vehicles (see Figure 9-1) that not only perform efficiently but also have the potential to recycle waste products into clean-burning sources of energy. U.S. federal law mandated significantly lower emissions on diesel engines nationwide by late 2006, and modern federal standards have significantly reduced the levels of sulfur in diesel fuel.

As fuel prices rise and nations compete (sometimes violently) for dwindling sources of oil, efficiency and power are excellent reasons for replacing your gas-guzzler with a vehicle that saves you money because it goes farther on less fuel and gives you the satisfaction of knowing that you’re doing your bit to protect the environment.

Figure 9-1: A clean diesel vehicle.

The Pros and Cons of Diesels

If you’re considering buying a new set of wheels, take a good look at this chapter on the new clean diesels as well as the alternatively fueled vehicles that I cover in Chapter 10 before you decide what to buy. This section helps you weigh the advantages and disadvantages of diesel-powered vehicles.

To help you accurately compare diesel vehicles with traditional gasoline-powered and alternatively fueled vehicles, here are some commonly held positive and negative beliefs about diesels, plus some facts to consider:

PRO: Diesels get great mileage. This is true; they typically deliver 25 to 30 percent better fuel economy than similarly performing gasoline engines. Diesels also can deliver as much or more fuel economy than traditional gasoline-electric hybrids, depending on the models involved and whatever rapidly developing automotive technology achieves.

CON: Although diesel fuel used to be cheaper than gasoline, it now often costs the same amount or more. Diesel fuel is also used for commercial trucks, home and industrial generators, and heating oil, so as demand for diesel passenger vehicles grows, the price of diesel fuel is likely to continue to rise because of competition from those other users.

BUT: Even if the price goes up, diesel fuel would have to be 25 to 30 percent more expensive than gas to erase the cost advantage of a diesel engine’s greater fuel efficiency.

PRO: Diesel fuel is one of the most efficient and energy dense fuels available today. Because it contains more usable energy than gasoline, it delivers better fuel economy.

CON: Although diesel fuel is considered more efficient because it converts heat into energy rather than sending the heat out the tailpipe as gas-powered vehicles do, it doesn’t result in flashy high-speed performance. In some ways, a gasoline-powered engine is like a racehorse — high-strung, fiery, and fast — whereas a diesel engine is more like a workhorse — slower, stronger, and more enduring.

BUT: Because of the way it burns fuel, a diesel engine provides far more torque to the driveshaft than does a gasoline engine. As a result, most modern diesel passenger cars are much faster from a standing start than their gas-powered counterparts. Diesels with manual transmissions usually don’t have to be downshifted to easily pass other vehicles on the highway, and although they don’t reach the highest speeds of gasoline-powered cars, many diesels still can cruise quite handily at 100 miles per hour or more (providing you can find a place to do that legally!). What’s more, diesel-powered trucks, SUVs, and cars also can out-tow gas-powered vehicles while still delivering that improved fuel economy.

PRO: Diesels have no spark plugs or distributors. Therefore, they never need ignition tune-ups.

CON: Diesels still need regular maintenance to keep them running. You have to change the oil and the air, oil, and fuel filters. Cleaner diesel fuels no longer require you to bleed excess water out of the system, but many vehicles still have water separators that need to be emptied manually.

PRO: Diesel engines are built more ruggedly to withstand the rigors of higher compression. Consequently, they usually go much longer than gas-powered vehicles before they require major repairs. Mercedes-Benz holds the longevity record with several vehicles clocking more than 900,000 miles on their original engines! You may not want to hang onto the same vehicle for 900,000 miles, but longevity and dependability like that can sure help with trade-in and resale values.

CON: If you neglect the maintenance and the fuel injection system breaks down, you may have to pay a diesel mechanic more money to get things unsnaggled than you would to repair a gasoline system because diesel engines are more technologically advanced.

BUT: All types of vehicles need maintenance, and the increasing complexity of both traditional and alternative vehicles may require repair by specialized technicians that work at higher rates than the mechanics at your neighborhood garage.

Diesel technology is constantly being improved. Government pressure to produce low-emission diesel engines for passenger vehicles, trucks, buses, and farm and construction equipment has resulted not only in low-sulfur diesel fuels but also specialized catalytic converters, advanced filters, and other devices to cut down or destroy toxic emissions. There are also dual-fuel engines that run on natural gas but can switch to diesel if the gas supply runs out. To reduce dependency on dwindling supplies of petroleum, biodiesel fuels derived from agricultural and commercial sources are being developed. The section “Diesel fuel” later in this chapter tells you more about them.

What Makes It Go?

The basic difference between a diesel engine and a gasoline engine is that in a diesel engine, the fuel isn’t ignited by an outside power source like a spark plug. Instead, the fuel is sprayed into the combustion chambers through fuel injector nozzles just when the air in each chamber has been placed under such great pressure that it’s hot enough to ignite the fuel spontaneously. (You can find more-detailed information about this process in the later section “The diesel four-stroke power cycle.”)

Most conventional gasoline engines have compression ratios of around 8:1, which means that the volume of each cylinder is eight times larger when the piston is at the bottom of the cylinder than when the piston is at the top of the cylinder. Diesel engines may employ compression ratios of above 20:1. Because of this volume, and because the compressed air can reach very high temperatures, diesel engines must be built for greater strength and endurance.

Following is a step-by-step view of what happens when you start up a diesel-powered vehicle. In the later section “The diesel four-stroke power cycle,” you take a closer look at each step of the power cycle that converts all this into power to drive the vehicle.

The following details may vary from one vehicle to another, but the action remains pretty much the same. (You may find it fun to compare this description with the short overview of how internal combustion engines work in Chapter 4.)

1. When you first turn the key in the ignition, you’re asked to wait until the engine builds up enough heat in the cylinders for satisfactory starting. (Most vehicles have a little light that says “Wait,” but a sultry computer voice may do the same job on some vehicles.) Turning the key begins a process in which fuel is injected into the cylinders under such high pressure that it heats the air in the cylinders all by itself. The time it takes to warm things up has been dramatically reduced — probably no more than 1.5 seconds in moderate weather.

Diesel fuel is less volatile than gasoline and is easier to start if the combustion chamber is preheated, so manufacturers originally installed little glow plugs that worked off the battery to pre-warm the air in the cylinders when you first started the engine. Better fuel management techniques and higher injection pressures now create enough heat to touch off the fuel without glow plugs, but the plugs are still in there for emissions control: The extra heat they provide helps burn the fuel more efficiently. Figure 9-2 shows a glow plug in a precombustion chamber, which allows the glow plug to heat a smaller amount of air more quickly and efficiently. Some vehicles still have these chambers, others don’t, but the results are still the same.

Figure 9-2: Glow plugs provide extra heat to burn fuel more efficiently.

2. When everything is warm enough, a “Start” light goes on. When you see it, you step on the accelerator and turn the ignition key to “Start.”

3. Fuel pumps deliver the fuel from the fuel tank to the engine. On its way, the fuel passes through a couple of fuel filters (see Figure 9-3) that clean it before it can get to the fuel injector nozzles (see Figure 9-4). Proper filter maintenance is especially important in diesels because fuel contamination can clog up the tiny holes in the injector nozzles.

Figure 9-3: A diesel fuel filter.

Figure 9-4: Anatomy of a fuel injector.

4. In the most common type of modern diesel fuel system, called common rail direct injection (CDI) and shown in Figure 9-5, the fuel injection pump pressurizes fuel into a delivery tube called a rail and keeps it there under constant high pressure of 23,500 pounds per square inch (psi) or even higher while it delivers the fuel to each cylinder at the proper time. (Gasoline fuel injection pressure may be just 10 to 50 psi!) The fuel injectors feed the fuel as a fine spray into the combustion chambers of the cylinders through nozzles controlled by the engine’s engine control unit (ECU), which determines the pressure, when the fuel spray occurs, how long it lasts, and other functions.

Other diesel fuel systems use hydraulics, crystalline wafers, and other methods to control fuel injection, and more are being developed to produce diesel engines that are even more powerful and responsive.

5. At this point, the action moves to the cylinders, where the fuel, air, and “fire” meet. While the preceding steps get the fuel where it needs to go, another process runs simultaneously to get the air where it needs to be for the final, fiery power play.

On conventional diesels, the air comes in through an air cleaner that’s quite similar to those in gas-powered vehicles. However, modern turbochargers can ram greater volumes of air into the cylinders and may provide greater power and fuel economy under optimum conditions. A turbocharger can increase the power on a diesel vehicle by 50 percent while lowering its fuel consumption by 20 to 25 percent!

6. Combustion spreads from the smaller amount of fuel that’s placed under pressure in the precombustion chamber to the fuel and air in the combustion chamber itself.

Figure 9-5: A common rail fuel injection system.

The Fuel System

The fuel system in a diesel engine performs the same functions as it does in gas-powered engines and consists of many of the same parts. After the fuel gets to the cylinders, however, there’s a difference in the four-stroke power cycle that converts it into the power to drive the vehicle. The next section provides a closer look at that cycle.

The diesel four-stroke power cycle

Although some smaller diesel engines (on motorcycles and marine engines, for instance) operate with two-stroke power cycles, most automotive diesel engines use a four-stroke power cycle, which is similar to, but not the same as, the power cycle of a gasoline engine (see Chapter 7). Here’s how the diesel’s four-stroke power cycle works:

Stroke 1: Intake stroke (see Figure 9-6). The piston descends, the intake valve opens, and air is drawn into the cylinder.

Figure 9-6: Intake stroke.

Stroke 2: Compression stroke (see Figure 9-7). The intake and exhaust valves are closed as the piston moves upward and places the air under extreme pressure. As the pressure increases, the air heats up to the flash point (the point at which it causes the fuel to undergo spontaneous combustion). Just before the flash point is reached, fuel injectors spray fuel into the combustion chambers at the precise instant when ignition is to take place.

Figure 9-7: Compression stroke.

Stroke 3: Power stroke (see Figure 9-8). With the intake valve and the exhaust valve closed, the fuel ignites, and combustion forces the piston down. This driving power is transmitted through the transmission and the rest of the drive train to the wheels, causing the vehicle to move.

Figure 9-8: Power stroke.

Stroke 4: Exhaust stroke (see Figure 9-9). The exhaust valve opens as the piston rises and pushes the burned gases out of the cylinder.

Figure 9-9: Exhaust stroke.

Diesel fuel

Diesel engines run on diesel fuel, which is more efficient than gasoline because it contains 10 percent more energy per gallon than gasoline. It’s also safer than gasoline because its vapors don’t explode or ignite as easily as gasoline vapors.

When the exhaust from conventional diesel fuel was found to cause cancer, clean diesel engines were developed. Although thousands of conventional diesel fuel-burning vehicles are still on the road, public pressure and environmental organizations have prodded individual states and the federal government to enact legislation and fund replacement programs to take them out of use as quickly as possible.

Standard diesel fuel

Much stricter diesel fuel standards have had a huge impact on cleaning up diesel exhaust. By 2007, the sulfur content of diesel fuels was restricted to 15 ppm (parts per million) compared to the dirty diesel previously in use that averaged something like 550 ppm. This ULSD (ultra low sulfur diesel) is derived by extra refining of the same high-sulfur petroleum diesel oil as before, but biodiesel fuels derived from agricultural and waste products are becoming more popular in North America. I cover biodiesel fuel in the next section.

Standard diesel fuel (sometimes called diesel oil) comes in two grades: Diesel #1 (or 1-D) and Diesel #2 (or 2-D). Just as gasoline is rated by its octane, diesel fuel is rated by its cetane, which indicates how easy it is to ignite and how fast it burns. The higher the cetane number, the more volatile the fuel. Most diesel vehicles use fuel with a rating of 40 to 55. You won’t have to worry about which type to use because all diesel automakers specify Diesel #2 for normal driving conditions. Truckers use Diesel #2 to carry heavy loads for long distances at sustained speeds because it’s less volatile than Diesel #1 and provides greater fuel economy.

Don’t confuse diesel fuel grade ratings with API (American Petroleum Institute) categories for oils used to lubricate diesel engines. The later section “Changing the lubricating oil” contains a guide to these API categories and more information about them.

Diesel fuel also is measured by its viscosity, which has to do with its thickness and ability to flow. Like any oil, diesel fuel gets thicker and cloudier at lower temperatures. Under extreme conditions, it can become a gel and refuse to flow at all. Diesel #1 flows more easily than Diesel #2, so it’s more efficient at lower temperatures. The two types of oil can be blended, and most service stations offer diesel fuel blended for local weather conditions.

If you plan to drive in very cold weather, choose diesel fuel rated at least 10 degrees lower than the coldest temperatures you expect to encounter. Consult your owner’s manual for specifics.

Because emissions from conventional diesel fuel have been found to be extremely toxic to humans and other living things, until safer forms of this fuel are developed, be careful not to inhale the fumes while pumping it into your fuel tank. (The same goes for gasoline!)

The diesel fuel sold at truck stops is often cheaper than at service stations, and the fuel is fresher, too. Freshness is important because diesel fuel can easily become contaminated by the water vapor that condenses in fuel tanks, and although it’s rarely found in North America these days, really dirty fuel can contain fungus and other microbes that can clog filters and fuel injectors. If you find yourself at a station that arouses your suspicions, look for slimy stuff on the nozzle of the fuel pump. Try to fill up at a truck stop on a Saturday morning, when commercial trucking action is light. Weekday evenings are the worst times to buy because muscling a small vehicle into a crowd of big rigs isn’t easy!

Biodiesel fuel

Biodiesel fuels derived from agricultural materials have the potential to provide a clean-burning alternative to dwindling sources of petroleum.

Rudolph Diesel’s first engine was designed to run on peanut oil, and Henry Ford envisioned plant-based fuel as the primary fuel for transportation and partnered with Standard Oil to develop biofuel production and distribution. However, as this book goes to press, the only type of biodiesel fuel that can be used in vehicles in the United States and Canada without violating manufacturer’s warranties is B5, a blend of 5 percent biodiesel and 95 percent regular diesel. Most diesel engines run just fine on blends of up to 30 percent biodiesel.

For higher blends, the engine control unit’s (ECU) electronic fuel “mapping” system, which regulates timing, fuel/air mixture, and so on, has to be reprogrammed to perform efficiently. The reason is that, although there’s no mechanical difference between a diesel engine that runs on diesel oil and a biodiesel-burning engine, biodiesel has slightly different energy and burning characteristics than regular petroleum-based diesel.

Biodiesel vehicles in the U.S. have been modified by do-it-yourselfers and specialty shops so that they can use higher biodiesel blends and fuels made from a variety of substances. It’s possible to make biodiesel from most any crop-based oil, and the news is filled with stories about modified vehicles that run on biodiesel made from french-fry oil and other restaurant grease, fresh-pressed cottonseed oil, you name it. But some of these oils contain compounds that can eat through gaskets and may be prone to going rancid if stored too long. Also, because biodiesel is a better solvent than standard diesel fuel, it can remove deposits in the fuel lines. That sounds like a good thing, but those deposits may foul up fuel filters and fuel injectors as they move through the fuel system. As a result, federal standards for the chemical composition of biodiesel fuel must be in place before it’s available in widespread use and before automakers will permit its use under warranty in anything but very diluted amounts. This should happen very soon.

Emergency substitutes

Theoretically, diesel engines should be able to run on kerosene, certain airplane fuels, biodiesel in all blends between 5 percent and 100 percent, and home heating oil, but the key word here is “theoretically.” Do not use these oils in your vehicle except in absolute emergencies. Standards of refining, filtering, and blending these oils differ widely, and they can ruin your engine, void your warranties, and create a whole lot of trouble for you.

If you find yourself low on fuel in a remote area, look for trucking companies, food-processing plants, electric plants, hospitals, and farms. These places usually have diesel engines on the premises, and some good Samaritan may take pity on you and let you have some.

If you absolutely can’t find a source of diesel fuel, as a last resort borrow some home heating oil or buy some Jet-A fuel at a local airport. Diesel mechanics consider these substitutes to be like rotgut whiskey — it will get you there, but it’s not the best stuff for your system! Drive on these fuels only long enough to get to the nearest source of proper fuel.

The Electrical System

Diesels require more stored energy for starting than gasoline vehicles do, especially on cold days. Instead of just using the battery to enable the starter to crank the engine, a diesel must have sufficient power to enable the glow plugs to warm the combustion chambers and then must build up enough heat and compression in the cylinders to ignite the fuel. For this reason, diesels must possess considerably more battery capacity than conventional vehicles. Some diesels come equipped with two batteries; others feature a single oversized battery that may be more than 50 percent bigger than one found on a conventional vehicle. You can find instructions for jump-starting diesel batteries in the section “Caring for Your Diesel” later in this chapter.

Aside from this battery issue, electrical systems on diesels are pretty much the same as those on conventional vehicles; alternators, solenoids, and starters perform their usual functions. For information about these components, turn to Chapter 5.

The Emissions System

Along with much cleaner fuel, automakers are transforming the old, toxic diesels into vehicles with clean exhaust emissions by making dramatic changes to their emissions control systems. As of 2007, all diesels sold in the U.S. were clean diesels, and they’ll continue to get cleaner each year as new technologies for exhaust cleansing are developed. California has led the way in this area of change, and each year more and more states adopt its standards, which are stricter than those set by the federal government. Hopefully, the federal government will raise its standards as high as California’s (or higher!) as time goes on.

The first innovations in cleaner diesel emissions systems were the additions of the following components (you can see them in Figure 9-1):

A diesel oxide catalytic converter that cleans hydrocarbons from the exhaust stream

A diesel particulate filter (see Figure 9-10) that scrubs sooty particles from the exhaust, trapping them in the filter material and regularly hitting the filter with a burst of superheated gasses to burn up the particles

Figure 9-10: A diesel particulate filter.

A number of automakers have introduced additional emissions traps to their diesel passenger vehicles and light trucks. Here are two systems:

One system injects a mist of urea (a type of ammonia) that’s nontoxic, odorless, and biodegradable into the exhaust stream, where it bonds to toxic NOx emissions (nitrogen oxides) and breaks them down to nitrogen and water. Then the exhaust flow carries the residue into a selective reduction catalyst (SRC) where it’s burned away. The urea container must be refilled regularly, usually with each scheduled mechanical checkup.

The other system uses a new type of plasma catalyst to superheat and convert the NOx emissions into ammonia and then into harmless nitrogen gas.

Caring for Your Diesel

Regular maintenance is absolutely imperative if you want a diesel engine to last, and every diesel owner will probably encounter some pitfalls and problems. This section helps you deal with maintenance and repair issues — whether or not you choose to do the work yourself.

Although diesel engines require no ignition tune-ups and tend to last longer without major repairs than gasoline engines, they do require regular low-cost maintenance, mostly in the form of frequent oil and filter changes. The urea injection systems that reduce NOx emissions (see the previous section) also need refilling, which is usually done as part of regularly scheduled maintenance.

If you own a conventional gas-powered vehicle and you get sloppy about maintenance and don’t change the oil often enough, you’ll probably end up with an engine that has aged prematurely. If you own a diesel and do the same thing, you may end up with an engine that’s prematurely dead. The same goes for changing filters: A dirty fuel filter can impair a conventional vehicle’s performance, but dirty fuel can clog a diesel’s fuel injection system, and you may need expensive professional help to get back on the road again.

As a rule, you shouldn’t try to clean or adjust a diesel’s fuel injectors yourself, but if you maintain your vehicle according to the directions in the owner’s manual, they can last 100,000 miles or more. After all, truckers have always preferred diesels because they find them to be tough, reliable, and cheap to run and maintain.

Most diesels are designed so that the owner can perform regular maintenance chores without an undue investment of time and money. The following sections cover these tasks in general terms; your owner’s manual should contain the rest of the information you need.

If your owner’s manual doesn’t advise you on a specific maintenance task, or if you have no manual, amble on over to your dealership’s parts department and ask to see a copy of the service manual for your vehicle (some bookstores and public libraries may also have them). A quick look at the proper sections should tell you whether you can do the job yourself. If you’re not sure, ask one of the service advisors at your dealership to show you where the oil, air, and fuel filters are located and what’s involved in changing or servicing them. Most service facilities are pretty nice about that kind of thing. If the job really is easy, they don’t make enough on it to make lying to you worth the loss in customer goodwill; if the job isn’t so easy, they figure you’ll be happy to have them do it for you.

Changing the lubricating oil

Because diesel fuel is sometimes called diesel oil, be aware that the oil you have to change is not the fuel oil but the oil that lubricates the engine. This job requires lubricating oil that’s specially designed for diesel engines — not gasoline engines. After you understand that distinction, the actual work involved is the same as it is for conventional vehicles except that you have to do the task more often on a diesel.

Be sure to check your oil dipstick at least once a week (following the instructions in Chapter 2), and change the oil filter every time you change the oil (see Chapter 13 for instructions). Don’t be surprised if you change the lubricating oil in your diesel, run the engine for two minutes, and check the dipstick only to find that the new oil has turned pitch black; this is normal and not a reason to change the oil again immediately.

Your owner’s manual tells you the maximum interval you can wait between changes, but I believe that the more often you change the oil on any vehicle, the longer the vehicle will live and the healthier it will be. That goes double for diesels because extreme heat and pressure help to contaminate the lubricating oil more quickly. The cost of having a professional change the oil on a diesel engine can be from two to four times greater than on a gas engine. This may be extra motivation for doing this relatively simple job yourself.

Because the procedure is the same, all the instructions for changing oil and oil filters in Chapter 13 are relevant for diesels except for the oil classification codes. (The classification codes for automotive oils tell you which oil to use under a specific set of conditions.) Figure 9-11 shows what the API classification code symbol looks like on containers of diesel oil from reliable manufacturers.

Figure 9-11: The API symbol for diesel oil.

As new and improved oils appear on the market, these codes have changed from the original CA to CB to CC, and so on. Each new level can replace previous ones, and the earliest oils are considered obsolete. Unless your vehicle is several years old, your owner’s manual will list the proper API category oil to use. The manual also specifies a viscosity grade in the form of a number preceded by the initials “SAE.” This grade refers to the “weight” of the oil and the temperature conditions under which it will flow. Diesel lubricating oil comes in the same range of weights as oil for conventional vehicles, and you can find additional information on that in Chapter 13.

To be sure you’re putting the most-improved diesel oil in your vehicle, check out the most recent API classification codes at your dealership or auto parts store, or go to the American Petroleum Institute (API) Web site at new.api.org/certifications/engineoil/categories and click on Engine Oil Guide.

Changing the air filter

The air filter setup on most diesels is the same as on gasoline-powered vehicles, with the filter located inside the cold air collector box located under the hood. You can find directions for reaching the air filter in Chapter 8.

You have to take one big precaution when you change the air filter on a diesel: Always shut off the engine first. Diesel engines produce exceedingly powerful suction, and the air intake goes directly to the engine. Because almost anything can fly or drop into it — from nuts and bolts to your favorite hairpiece — you risk serious damage to the engine if you open the cold air collector box with the engine running.

Changing the fuel filters

Most diesels have two fuel filters: a “primary” filter located between the fuel tank and the engine, which cleans the fuel before it gets to the fuel transfer pump; and a “secondary” filter up near the engine, which gives the fuel a final cleaning before it gets to the fuel injectors. Both are usually easy to change, and your owner’s manual should show you how to do this job. On some diesels, the job is much like changing the oil filter on a conventional vehicle: You unscrew the old one, moisten the gasket of the new one with fuel, and screw it into place. Others have filters with replaceable cartridges; you just remove the old one and pop in the new one. There’s one catch to changing the fuel filter, however, and the next section has the details.

Bleeding and priming the fuel system

When you change the fuel filter or run out of fuel in a diesel vehicle, you must bleed the air bubbles out of the fuel system and then prime it to get a new supply of fuel circulating. Cranking the engine does the job but also wears down the battery, so most diesels include a manual primer pump and an air-bleed screw for the purpose of bleeding the system and priming it. On many vehicles, you simply pump the primer’s handle to get the fuel moving, and then you turn the air-bleed screw until a hissing noise tells you that the air is escaping. Just keep pumping until all the air leaves and the noise ceases; then tighten the air-bleed screw and replace the pump handle.

Because bleeding and priming the fuel system is something that you may need to do fairly often, I suggest that you check the equipment and procedure for any model you’re interested in purchasing to be sure that you can do this job quickly and easily.

Draining water separators

Diesel fuel can easily become contaminated by water because diesel fuel absorbs water more than gasoline does. For this reason, many diesel vehicles feature a gadget called a water separator that collects water from the fuel. It’s usually located on or near the fuel filter. If your vehicle doesn’t have one, I strongly suggest that you have one installed. The part shouldn’t be terribly expensive, and it can save you a bunch of money on repairs.

Although a few water separators are self-cleaning, most need to be manually drained: You just turn a little drain valve called a petcock and empty the water from the collection chamber of the separator.

It’s a good idea to check the water separator weekly at first to see how fast it fills up under normal conditions when you’re driving on fuel from your usual source. If the fuel contains a lot of water, you may want to consider buying it elsewhere.

Jump-starting diesel batteries

Even though diesel-powered vehicles can have dual batteries or one oversized battery (refer to the earlier section, “The Electrical System”), it’s possible to jump-start a diesel from the battery on a conventional gasoline-powered vehicle.

To avoid confusion, in this section I call the vehicle with the dead battery the disabled vehicle and the one you’re jumping the start from the source vehicle. Follow these steps to jump-start a dead diesel battery:

1. Make sure that both vehicles are in Park or Neutral with the parking brakes on.

2. Turn on the heater on the disabled diesel vehicle to protect the electrical system from surges in voltage.

3. Make sure that the lights and other electrical accessories on the disabled diesel vehicle are off.

4. A vehicle with dual batteries usually has thicker cables on one of the batteries. If either vehicle has dual batteries, always attach the jumper cables to the battery with thicker cables.

If either vehicle has dual batteries with cables of the same thickness, use either battery for the jump. If a vehicle has only one battery, just be sure to hook the cables up in the proper order.

5. Connect the clamp on one of the jumper cables to the positive terminal of the disabled vehicle’s battery.

The positive terminal should have a (+) or a red cover on it.

6. Connect the other end of the same jumper cable to the positive terminal of the source vehicle.

7. Connect one end of the other jumper cable to the negative terminal (-) of the source vehicle.

8. Here’s the tricky part: Connect the other end of that jumper cable to an unpainted, metallic part of the disabled vehicle.

I often use the bracket that keeps the hood up, but any such part will do as long as it’s not near the battery, belts, or any other moving parts of the engine.

9. Start the engine on the source vehicle.

10. Start the engine on the disabled vehicle, and let both engines run for a minute or two, more if the battery has been dead for a long time.

11. Turn off the engine of the source vehicle. (Leave the disabled vehicle’s engine running.)

12. Remove the cable from the unpainted metal part of the disabled vehicle.

13. Disconnect the cable from the positive terminals of both vehicles.

14. Disconnect the cable from the negative terminal of the source vehicle.

15. The disabled vehicle should be driven around for at least 15 minutes to ensure that the battery is fully charged.

If you jump-start a dead diesel vehicle and the battery dies the next time you try to start the car, you probably need a new battery. Be sure to get the proper one for your vehicle’s make, model, and year.

Getting Started on a Frosty Morning

Diesel drivers everywhere are thankful that diesels have become easier to start in cold weather. Most turn over within 1.5 seconds of turning on the ignition.

Metal cylinder walls become very cold when the temperature drops, so most vehicles are harder to start in cold weather. Because diesel engines require much higher temperatures to fire the fuel, they’ve always been harder to start in cold weather than gasoline-powered vehicles. To warm things up before the engine can run, a variety of heaters have been developed that keep various parts of the vehicle warm and snuggly even when it isn’t being driven. Some of these gadgets may be on the vehicle when you buy it; others you can buy and install later on if the need for them arises.

If you’re planning to buy a diesel, be sure to ask which heating devices are included in the purchase price. If you live in a cold climate or do much traveling, consider having several devices available for extreme weather conditions. The following sections describe some of your options.

Block heaters

Many diesels come equipped with built-in electric-powered block heaters to keep the engine block warm overnight. You just park the vehicle, plug the heater cord into a heavy-duty three-pronged extension cord, and then plug the extension cord into a 110-volt electrical socket that can handle a three-pronged plug. When shopping, don’t skimp on the length of the extension cord — it can be 50 feet to a socket from a motel parking lot! I’ve been told that in Alaska, where a block heater is vital, electrical outlets are built right into some parking meters. I doubt that anyone tries to beat those meters, especially at –40°F!

If your vehicle doesn’t have a block heater, you can buy one and have it installed. Various types are available, but immersion -type heaters are the most popular.

When buying a heater, consult the charts at an auto parts store or dealership to match the wattage of the heater to the size of your engine and the range of weather you expect to encounter. When plugged in, a high-wattage heater will run up your electric bills unnecessarily if you have a small engine or don’t expect the temperature to go below zero very often.

Battery warmers

If your diesel doesn’t start in cold weather and you remembered to plug in the block heater, your battery may be the culprit. Batteries can lose 35 percent of their power at 32°F and as much as 60 percent at 0°F. Because the battery has to supply the glow plugs with sufficient juice to get things warmed up (refer to the earlier section, “What Makes It Go?”), a frostbitten battery isn’t of much use on an icy morning.

This problem has two remedies: You can buy a battery with greater capacity (providing that there’s room for one under the hood), or you can buy a battery warmer. The two most popular models, both of which simply plug into a nearby 110-volt socket, are

The “hot plate” warmer, which simply slides under the battery like a cookie sheet and warms its little toesies.

The “electric blanket” warmer, which wraps around the battery and uses more current than the hot plate version to deal with really frigid situations.

Oil warmers

You can buy a heated dipstick to heat the oil in the engine crankcase (you just trade it for your normal dipstick and plug it into an electrical outlet) and a host of other gadgets to warm the coolant in the engine and the fuel in the fuel lines. (Most people don’t need all this stuff, but for my readers in Alaska, Canada, and other cold climates, I want to cover the subject thoroughly.)

Here’s a handy hint that may work in a pinch: On a day when your block heater isn’t able to combat the cold effectively, if you have an electric hair dryer and a long enough extension cord to get it to the vehicle, try turning the dryer on and putting the nozzle into the car’s air inlet duct. The warm air should help your engine warm up faster.

What not to do on a frosty morning

Never use engine-starting fluids to start your engine — no matter how eager you are to get underway. The ether in these fluids can ignite at such low temperatures that you risk a fire or an explosion, either of which can mean severe damage to both yourself and your precious diesel. Although the containers carry instructions, measuring the “safe” proportions required is just too hard. If you feel that you must use this stuff, I suggest that you have a starting-fluid injection kit installed instead; it’s safe and effective. Just stay away from those spray cans!

Finding a Reliable Diesel Mechanic

If you need professional diesel maintenance or repair and your vehicle is out of warranty, you may want to check around for a good independent diesel mechanic so that you can compare prices with those of the dealership or get a second opinion on major surgery. One way to find a good independent diesel mechanic is to look in your local yellow pages under “Automobiles, Repair” (or something similar) for a shop whose ad carries the logo of the Association of Diesel Specialists (ADS). The ADS authorization goes to repair facilities that send their mechanics to factory schools for instruction, maintain standards of cleanliness, and meet requirements for stocking the tools and parts to deal properly with a variety of diesel systems. (Chapter 22 is devoted to finding and maintaining a good relationship with a mechanic; it also tells you how to get satisfaction on complaints about labor or services.)