C i r c l e 5 3 Cooling System o n C There will be two questions on the a r ASE P2 test that deal with cooling d systems, parts and products. he cooling system includes the radiator, radiator T cap, coolant reservoir, fan (electric or mechanical), fan clutch (if equipped with a mechanical fan), water pump, thermostat, hoses, belts and antifreeze. Related parts include the coolant temperature sensor and fan relay. The radiators in most late-model vehicles are alu- minum with plastic end tanks. Most older vehicles have copper/brass radiators. Both types are vulnerable to in- ternal corrosion caused by coolant neglect. Replacement Automatic Transmission Braking System Cooling System Drivetrain Electrical System Emission Control System Engine Parts Gaskets and Seals Exhaust System Fuel System HVAC Ignition System Manual Transmission/Transaxle Steering & Suspension radiators should have the same cooling capacity (or bet- ter) than the original and the same hose connections. Cooling capacity is determined by the thickness of the radiator, the number of fins and tubes and/or the de- sign of the fins and tubes. Increased cooling capacity is recommended for towing and performance applica- tions. The water pump is the heart of the cooling system. It is belt-driven and consists of a plastic or stamped steel impeller mounted on a shaft inside a cast or stamped steel housing. The pump is usually mounted on the www.counterman.com OCTOBER 2007 COUNTERMAN 53 front of the engine. On some over- allows coolant to flow to the radia- fan relay, coolant temperature head cam (OHC) engines the pump tor. The thermostat continues to switch or a wiring problem that pre- is mounted under the timing belt cycle open and shut so the engine vents the fan from coming on can and requires considerable labor to re- can run within a certain tempera- cause the engine to overheat. place. For this reason, you should ture range. This is very important The major hoses in the cooling recommend replacing the pump if on late-model vehicles with com- system include the upper and lower the timing belt is being replaced for puter engine controls because en- radiator hoses (the lower one usu- scheduled maintenance (recom- gine temperature affects the fuel ally attaches to the water pump and mended every 60,000 to 100,000 feedback control loop, emissions, the upper usually attaches to the miles, depending on the application). fuel economy and performance. thermostat housing), plus a pair of The service life of the water pump If the thermostat sticks shut, the heater hoses (one inlet and one out- and timing belt is about the same, so engine will overheat. If it fails to let) and various connecting hoses changing both at the same time can close, the engine will be slow to and bypass hoses depending on the save the vehicle owner money on warm-up and the heater may not application. Replacement hoses future repairs. Water pumps don’t put out much heat when the must be the same length and diam- last forever, and leaks around the weather turns cold. Fuel economy, eter as the original. New clamps pump shaft seal and bearing can emissions and engine wear will also should also be installed when hoses quickly lead to overheating. Erosion suffer. Under no circumstances are replaced. Hoses should be re- of the blades on a plastic impeller or should an engine run without a placed if leaking, cracked or a loose impeller can also cause over- thermostat. Replacement thermo- bulging. Electro-chemical degrada- heating. Any water pump that is stats should have the same rating as tion due to coolant neglect can cause leaking, making noise or has exces- the original. A slightly hotter ther- hoses to fail from the inside out. sive shaft play should be replaced. mostat may be used during cold The coolant is a mixture of ethylene Replacement options include re- weather for increased heater output, glycol antifreeze and water (typically manufactured and new pumps. but a colder thermostat should not a 50/50 mix). This combination pro- The water pump may also be be used on engines with computer vides freezing protection down to -34 driven by a V-belt or a flat serpen- controls. Other items that may be degrees and boilover protection up to tine belt. The same belt may also needed when changing a thermostat 265 degrees F with a 15 PSI radiator drive other engine accessories. Belts include a new thermostat housing cap. The condition of the coolant is deteriorate with age and should be and gasket or sealer. just as important as the strength be- replaced if frayed, cracked, glazed To improve cooling, a fan is cause corrosion can attack the system or oil-soaked. Replacement belt needed to pull air through the radi- from within if the coolant is neg- length and width must be the same ator when the vehicle is stopped or lected. The recommended replace- as the original. On vehicles with ser- traveling at low speed. Older rear- ment interval for traditional “green” pentine belts, the automatic ten- wheel-drive vehicles may have a antifreeze is two years or 30,000 sioner may also need to be replaced belt-driven fan with or without a miles. For the newer extended- life if it is sticking, making noise or can- clutch. The clutch allows some slip- coolants, the change interval can be not maintain proper belt tension. page and is used to reduce fan noise as long as five years or 150,000 miles. Belt idler pulleys should also be re- at high RPM and to improve fuel Most long-life coolants use organic placed if noisy, worn or sticking. economy by reducing drag. Exces- acid technology (OAT) additives that For temperature control, the cool- sive slippage in the clutch, however, are different from those used in stan- ing system requires a thermostat. It may reduce airflow and cause the dard antifreeze. Long-life coolants is usually located in a housing engine to overheat at low speed. may contain special dyes to distin- where the upper radiator hose con- Most people don’t know it, but the guish them from ordinary antifreeze, nects to the engine. The thermostat fluid inside a fan clutch breaks such as the orange dye in General does two things: First, it allows the down over time, causing the clutch Motor’s Dex-Cool coolant. Other engine to warm up quickly (which to slip more than it should. This can manufacturers use different colors. If reduces cold emissions and fuel lead to overheating in a high- the cooling system is low, it should be consumption) and second, it main- mileage vehicle. Most newer vehi- topped off with the same type of an- tains a consistent operating temper- cles have one or two electric cooling tifreeze as the original. Even so, the ature (also important for low fans mounted behind the radiator type of coolant can’t always be iden- emissions, good fuel economy and and a few have hydraulic fans tified by its color, so most long-life performance). The thermostat has a driven by power steering fluid. antifreeze now uses a “universal” temperature-sensitive valve that re- Electric fans are powered through a chemistry that is compatible with all mains closed and blocks the flow of relay and controlled by a coolant types of coolants and makes and coolant until the engine reaches 195 temperature switch or the engine models of vehicles. t to 210 degrees F. It then opens and computer. A failure of the fan motor, 54 COUNTERMAN OCTOBER 2007 www.counterman.com.