Chapter 11

The Cooling System Up Close

In This Chapter

Looking at radiators and coolant recovery systems

Shooting the breeze about the fan

Understanding water pumps

Talking about thermostats, heater cores, and transmission coolers

Airing the truth about air conditioners

With all that air, fuel, and fire stuff going on in its engine, your vehicle needs something to help it keep a cool (cylinder) head! Because water is usually cheap, plentiful, and readily available, auto manufacturers have found it to be the simplest answer to the problem. A few have found that air is even cheaper and more abundant; they designed the air-cooled engines on the old Volkswagens, but aside from some VW bugs and air-cooled Porsches that are still on the road, there are few air-cooled vehicles available in the United States these days.

Of course, nothing is as simple as it seems. Automakers have added some gizmos to keep the water in the engine from boiling too easily: a water pump, fan, radiator, thermostat, and coolant. There’s also a transmission cooler to keep the transmission from overheating and an air-conditioner to keep you from overheating. Together they comprise your vehicle’s cooling system (see Figure 11-1).

The cooling system is highly efficient. It usually requires almost no work to keep it operating — just a watchful eye for leaks and an occasional check or change of coolant. Of course, some vehicles have more complicated systems or variations on the theme, but in general, if you understand the way the basic cooling system works, you should have little trouble dealing with the one in your vehicle. Whether you do the work yourself or have it done professionally, keeping the cooling system in good shape will go a long way toward “keeping your cool” when things heat up on the road.

Figure 11-1: The cooling system.

This chapter explores the cooling system part by part. Chapter 12 shows you what to do if your vehicle overheats and how to maintain and troubleshoot the cooling system and make easy repairs. Chapter 21 helps you get out of trouble if your car overheats on the road.

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

Coolant/Antifreeze

To keep the water in the cooling system from boiling or freezing, the water is mixed with coolant or antifreeze. In the interest of brevity, I just call it “coolant” throughout this book.

Most coolants contain about 95 percent ethylene glycol, a chemical that stops water from freezing or boiling even in extreme temperatures. (Ethylene glycol is toxic; there are nontoxic coolants that contain propylene glycol instead. See Chapter 12 for more.) In addition to the glycol, coolant also contains rust, corrosion, and foaming inhibitors, so coolant does more than just keep the water in the system in a liquid state: It also helps to prevent the formation of rust on the metal surfaces of the engine and the radiator, lubricates the water pump, and keeps the liquid from foaming as it circulates through the system. Since the early 1960s, auto manufacturers have designed the cooling systems of most vehicles for a 5 0/50 mixture of ethylene glycol and water, which is still generally considered the proper proportion of coolant to water for the cooling systems of most vehicles. (I often refer to the coolant and water mixture as “liquid” in this chapter.)

Today’s engines require specially formulated coolants that are safe for aluminum components. There are long-life (sometimes called “extended life”) coolants with organic acid rust and corrosion inhibitors that promise to last for as long as five years. Automakers use some of these coolants as original fluid in new vehicle radiators made of aluminum (they can’t be used in anything except aluminum radiators).

Due to differences in Japanese, Korean, European, and American compounds, you can shorten coolant life by putting the wrong stuff in your vehicle’s cooling system. So make sure that you use the automaker’s recommended coolant to ensure the longest life and best protection for your vehicle.

If your cooling system is operating properly, you shouldn’t have to keep adding liquid to it. Chapter 2 shows you how to check the level and condition of the liquid in the cooling system, and Chapter 12 shows you how to add liquid or flush the system and replace the liquid in it.

The Radiator

When the fuel/air mixture is ignited in the cylinders, the temperature inside the engine can reach thousands of degrees Fahrenheit. It takes only half that heat to melt iron, and your engine would be a useless lump of metal in about 20 minutes if your vehicle couldn’t keep things cool. Naturally, the coolant (and water) that circulates from the radiator through the top radiator hose to the thermostat and around the cylinders in the engine block gets very hot, so it’s continually circulated back to the radiator via the bottom radiator hose, where it cools off before heading back to the scene of the action. The radiator’s pressure cap keeps your car from boiling over, and the coolant recovery system holds extra coolant so it doesn’t overflow onto the roadway.

The hoses

The radiator is designed to cool the liquid quickly by passing it over a large cooling surface. The liquid enters the radiator through the top radiator hose, which is usually connected to (you guessed it) the top of the radiator (refer to Figure 11-1). As the liquid descends, it runs through channels in the radiator that are cooled by air rushing in through cooling fins between the channels. When the liquid has cooled, it leaves the radiator through the bottom radiator hose (surprise!). This hose usually has a spring inside it to prevent it from collapsing when the water pump draws coolant from the radiator. (If it collapses anyway, Chapter 12 has instructions for replacing it.)

Smaller-diameter hoses also lead from your engine to the heater core (see the later section, “The Heater Core”). Some vehicles have a small bypass hose near the thermostat as well (see the later section, “The Thermostat”). These hoses are an important part of the cooling system because they’re designed to carry the liquid in it from one component to another.

The coolant recovery system

A coolant recovery system is a plastic or metal container with two little hoses coming out of the cap (see Figure 11-2). One hose leads to the radiator, and the other serves as an overflow pipe for the container, which holds an extra supply of water and coolant in case the system loses any.

When your cooling system heats up and starts to overflow, the liquid pours back into the recovery system reservoir instead of pouring out of the radiator overflow pipe and onto the ground. When the system cools off, the pressure drops and the liquid is drawn out of the reservoir and back into the radiator. This process not only saves you coolant but also protects animals and children from sampling puddles of the toxic stuff.

Figure 11-2: A coolant recovery system.

Some of today’s new vehicles have pressurized reservoirs. In these cases, you may find the pressure cap (which I get into in the next section) on the reservoir and not on the radiator. I’ve been told by radiator specialists that, on some vehicles, this system doesn’t work very efficiently because, as the pressure builds up in the coolant reservoir, it forces the coolant out of the overflow pipe and onto the street. Not only is this overflow a toxic hazard, but as the coolant supply diminishes, the chance of the engine overheating increases, leading to a vicious circle.

Many recovery systems are considered “sealed” because you add water and coolant by opening the cap on the reservoir rather than on the radiator. You also check the level of liquid in the system by seeing whether it reaches the “Max” level shown on the side of the container rather than by opening the radiator and looking inside. (For instructions on adding liquid to a sealed system safely, see Chapter 12.)

The pressure cap

To further retard the boiling point of the liquid in the cooling system, the entire system is placed under pressure. This pressure generally runs between 7 and 16 pounds per square inch (psi). As the pressure increases, the boiling point rises as well. This combination of pressure plus coolant gives the liquid in your cooling system the capability to resist boiling at temperatures that can rise as high as 250°F or more in some vehicles.

To keep the lid on the pressure in the system and to provide a convenient place to add water and coolant, each radiator has a removable radiator pressure cap located on either its radiator fill hole or its coolant recovery system.

The pressure cap has two valves: a pressure valve that maintains a precise amount of pressure on the liquid in the system, and a vacuum valve that allows the liquid to travel back into the radiator from the recovery reservoir.

Pressure caps are relatively inexpensive, but if you have a cap that isn’t working properly, or if you have the wrong type of cap, you’ll be amazed at the amount of trouble it can cause. For example, if the gasket inside the cap isn’t working, the pressure in the system will escape, allowing the liquid to boil at a lower temperature. A modern cooling system that has been designed to operate normally at temperatures over 212°F, and that is filled with liquid and in perfect condition, will still continually boil over if the radiator cap isn’t operating efficiently. That boiling liquid will be forced into the overflow system, and your vehicle’s engine will overheat. An overheated engine can cause an inconvenient highway breakdown and possible danger to your engine.

If your vehicle overheats on the highway, Chapter 21 can get you cooled down safely. Chapter 12 offers remedies for other overheating problems.

The Fan

Air rushing through the radiator cools things off when you’re driving merrily down the highway, but a fresh supply of air doesn’t move through the radiator fins when the vehicle is standing still or crawling its way through heavy traffic. For this purpose, the fan is positioned so that it cools the liquid in the radiator (refer to Figure 11-1). Today, most fans have a plastic shroud that funnels air through the radiator. Some vehicles have air dams that help force the air up through the radiator from below.

Originally, the fan operated in connection with the water pump, and they were both driven by a single fan belt that ran around a pulley connected to the alternator. This fan belt drove the fan as long as the engine was running. Almost all fans today are electric and thermostat-controlled, not hooked by belts to the engine or water pump. These fans only come on when they need to. Because the air rushing past them allows these fans to simply “coast” at high speeds, the engine doesn’t have to work as hard or burn as much fuel to supply the power that the fans would normally consume.

Some vehicles now have two fans because styling changes that have lowered the profile of the hood area have caused radiators to get lower and longer, meaning that a single fan doesn’t cover the entire surface. These two fans are sometimes run by electric thermostats that aren’t connected to the water pump at all (I cover the water pump in the next section).

The Water Pump

The water pump (see Figures 11-1 and 11-3) draws the cooled liquid from the radiator through the bottom radiator hose and sends it to the engine, where it circulates through water jackets located around the combustion chambers in the cylinders and other hot spots. Then the liquid returns to the radiator to cool off again. An accessory belt connected to the crankshaft drives some water pumps, while some overhead cam engines drive the water pump with the timing belt. Chapter 2 tells you how to check accessory belts, and Chapter 12 has instructions for adjusting and replacing them.

Figure 11-3: A water pump.

If the timing belt drives your water pump, the water pump will be difficult to see unless you remove the plastic timing belt cover.

The Thermostat

The thermostat is the only part of the cooling system that does not cool things off. Instead, it helps the liquid in the cooling system warm up the engine quickly.

The thermostat is a small, metal, heat-sensitive valve (see Figure 11-4) that’s usually located where the upper radiator hose meets the top of the engine. (On a few vehicles, you find the thermostat where the bottom hose joins the engine. Your owner’s manual should tell you where yours is.) When it senses hot liquid, the thermostat allows the liquid to pass through. But when the thermostat senses that the liquid is cold (like when you first start your engine in the morning), it closes and doesn’t allow the liquid to circulate through the radiator. As a result, the liquid stays in the engine, where it gets hot as the engine warms up, and in turn, the increasing heat of the liquid helps the engine to warm up more quickly. As a result, the vehicle runs more efficiently and burns less fuel.

Figure 11-4: A thermostat.

The Heater Core

The heater core is located inside the vehicle between the instrument panel and the firewall (refer to Figure 11-1). It looks like a miniature radiator minus the fill neck and cap. The purpose of the heater core is to provide heat for the passenger compartment. The same liquid that the water pump circulates throughout the engine also circulates through the heater core when the engine is operating. When you get chilly, you can direct air across the heater core and heat the interior of your vehicle by turning on the inside fan. Because the heater core is relatively passive, it usually doesn’t need attention unless it breaks.

The Transmission Cooler

Vehicles with automatic transmissions have a transmission cooler located in or near the bottom or side of the radiator (refer to Figure 11-1). The transmission fluid circulates from the hot transmission to the cooler, which cools it and returns it to the transmission. If the transmission cooler on your vehicle is working properly, you don’t need to monkey with it. If it leaks, have it repaired by a professional.

Air Conditioning

Air conditioning is now standard equipment on most vehicles rather than an option. It uses refrigerant to remove the heat from the air (rather than cooling it) and a blower to send the cool air into the passenger compartment.

Until 1992, a refrigerant called CFC-12 (commonly called Freon) was standard on most vehicles. When it was found to contribute to the depletion of the ozone layer, CFC-12 was phased out and replaced by R-134a. Production of CFC-12 ceased at the end of 1995, and although the stuff can be recycled, supplies may be limited. The biggest improvements since the development of R-134a are better, less-porous hoses and seals so that the smaller R-134a molecules don’t leak out like they used to. A new CO₂ refrigerant system that has been in the prototype stage since around 2002 may be the next major development in vehicle air conditioning systems.

If your vehicle was built before 1992, you may have trouble getting Freon if you need to replace the refrigerant in your vehicle’s air conditioner. Conversions to an alternative refrigerant (R-134a) are expensive, so think about this fact before buying a pre-1992 used vehicle or undertaking expensive repairs on an older vehicle that you already own; the vehicle may not be worth as much as it would cost to rebuild the air conditioning system. Chapter 12 tells you how to troubleshoot problems with your air conditioner and provides tips on servicing it and finding out what it would cost to convert from CFC-12 to R-134a refrigerant.