Whether a vehicle is powered by a gasoline engine or a diesel engine, they both need a cooling system to keep the engine from overheating. Almost a third of the energy thats released in the combustion chamber is absorbed by the engine and cooling system as waste heat. Its enough BTUs (British Thermal Units) to heat a small house. So all the parts in the cooling system must be working efficiently to get rid of that heat.

In order to keep the cooling system in good working order, its important to play detective keep your eyes peeled for signs of trouble.

The first symptom of cooling system trouble is often a coolant leak. It may be nothing more than a little seepage around the water pump, the bottom of the radiator or a hose. If the driver fails to notice the leak, the next clue will likely be a temperature gauge or idiot light that says the engine is running hotter than normal. If he continues to ignore the warning, the next indication of trouble may be steam belching from under the hood as his engine clatters to a halt.

Loss of coolant, a stuck thermostat or a dead electric cooling fan may all cause an engine to run hot and overheat. But so too can exhaust restrictions (a plugged catalytic converter) or a defective water pump (loose or badly eroded impeller).

Severe overheating can be very damaging to todays engines, especially those with aluminum cylinder heads on iron blocks. When temperatures soar, cylinder heads swell and can warp and crack, pistons can scuff and valves may stick. Thats why inspecting and maintaining the cooling system is so important. A little maintenance now can save a lot of repair expense later.

Motorists used to be fairly religious about changing their antifreeze every couple of years. But with todays long-life coolants, the need for maintenance has been played down. One-hundred-thousand-mile tune-up intervals mean a lot of vehicles seldom visit a service facility except for oil changes (unless theyre brought in on a tow truck for repairs). Even then, they may not receive the attention they deserve. Consequently, we have a whole new generation of drivers who ignore the need for maintenance until its too late. We call this "underperformed maintenance" and it adds up to millions of dollars in parts and services that are not being sold.

SELLING COOLING SYSTEM PARTS
Most cooling system parts, except for antifreeze, are not sold until the original parts have failed. Though most belt and hose manufacturers recommend replacing belts and hoses every four or five years for preventive maintenance, these parts are seldom replaced until they fail. The incidence of failure goes up sharply as time and miles add up, and the chance of a hose or belt failing after five years or 60,000 miles is double that of ones that are only three years old. Add another two years, and the risk of a failure skyrockets.

Serpentine belts usually outlast V-belts because they run cooler, but slipping, glazing and age hardening can make them noisy. If a belt is starting to make noise, it needs to be replaced. Its also a good idea to inspect the idler pulleys and automatic belt tensioner. On high-mileage vehicles (those with over 80,000 miles on them), its a good idea to replace the tensioner pulley when a serpentine belt is changed. Why? Because the spring and bearings inside the tensioner are probably reaching the end of the road.

If a customers cooling system has boiled over for any reason, its also a good idea to replace the thermostat even if the old one was not the cause of the boilover. The wax element inside a thermostat can be damaged if the engine gets too hot which may cause the old thermostat to stick or fail in the not-too-distant future. Better to prevent trouble now by replacing the thermostat than to have another breakdown a few thousand miles later.

WATER PUMPS
The water pumps job is to keep the coolant circulating between the engine and the radiator. Many late-model water pumps have aluminum or stamped steel housings to reduce weight, which also means they must usually be replaced with a new pump rather than a remanufactured pump when they fail. Reman pumps for older applications with cast iron housings are still common, but availability is much less for the newer engines.

Labor is another reason why many customers want a new pump rather than a reman pump if their pump has to be replaced. The labor to change a pump on many OHC engines where the pump is buried behind the timing belt can run three to five hours. Its an expensive repair so many customers want a replacement pump that provides the best longevity and warranty.

Water pump failures are usually the result of a seal or bearing failure that causes the pump to leak. Severe erosion or damage to the internal impeller may also be a reason for replacing the pump. In both cases, the underlying cause is often a dirty cooling system. Contaminants tend to collect inside the pump around the shaft seal. Here they accelerate wear and eventually ruin the seal.

Most experts recommend thoroughly cleaning and flushing the cooling system (twice) before replacing the old pump to get rid of all the contaminants and to provide the best possible operating environment for the new pump.

BELT-DRIVEN FANS & CLUTCHES
There are still a lot of vehicles on the road (mostly trucks) that have a belt-driven cooling fan, and many of these fans have a viscous clutch to reduce noise and drag on the engine. There are two types: nonthermal and thermal. The nonthermal variety are designed to slip a predetermined amount so the fan speed peaks out around 2,200 to 2,400 rpm. The thermal variety contains a bimetal thermostat that increases or decreases the amount of slippage depending on how much heat the radiator is giving off.

The performance of a fan clutch will degrade over time by about 200 rpm a year. Eventually the fan clutch reaches the point where effective cooling is no longer possible and overheating results.

Symptoms of a defective fan clutch include:

• Oily steaks on the clutch housing;
• Play in the clutch bearing (wobbling);
• Freewheeling (a good fan should not turn more than one to one-and-a-half turns if spun by hand);
• Binding (frozen).

Most experts recommend replacing the fan clutch at the same time as the water pump because both have about the same life expectancy.

ELECTRIC COOLING FANS
Most late-model vehicles have electrically driven cooling fans. Some may have a pair of fans mounted side-by-side, while others have separate fans for the radiator and A/C condenser.

If the fan motor fails, the cooling fan wont be able to pull air through the radiator or condenser when called upon to do so. This can lead to overheating and poor A/C cooling performance. Most fans are designed to come on when the A/C is on, or when the coolant temperature reaches a certain point. If the fan does not come on when it is supposed to, there is a problem in the fan switch, wiring, coolant sensor, fan relay or fan motor. If additional testing isnt done to isolate the fault, your customer may end up replacing the wrong part.

RADIATORS
Most late-model cars have aluminum radiators, which have proved to be fairly durable provided the coolant is maintained to keep corrosion in check. Most older vehicles used copper/brass radiators that has soldered seams and joints. "Solder bloom" in these older radiators can be a serious problem when the coolant is neglected.

On some newer vehicles, the radiator, A/C condenser and cooling fan are all part of a "cooling module." The parts are combined into one assembly to make installation easier when the vehicle is built at the factory. But this approach also makes for expensive repairs when any of these parts fail later in the vehicles life because the whole assembly may have to be replaced, not just the part that failed.

Any radiator can corrode internally or suffer stone damage that causes it to leak. The up front location of the radiator usually means it is a casualty if the vehicle takes a hard hit in the front.

Radiators can sometimes be repaired, but often the repairs cost as much as, if not more than, a brand new radiator. Plus, theres the inconvenience of having the vehicle tied up for a day or two while the radiator shop cleans, welds, glues, solders or recores the old radiator.

Aftermarket radiators are a good alternative for many customers because they reduce down time, and they come with a warranty thats better than that offered by many radiator repair shops.

Dont forget, anyone who is replacing a radiator will also need new hoses, clamps and antifreeze. Your customer will need a new radiator cap, too. The cap is especially important because it holds pressure in the system and raises the boiling temperature of the coolant. Pressurization also prevents the formation of steam bubbles inside the engine, which improves cooling efficiency. Cap pressures can range from four pounds up to 18 pounds. If it cant hold pressure, the system can lose coolant and overheat. Replacement caps must have the same pressure rating as the original.

HEATER CORES
The heater core is a heat exchanger thats usually located inside the passenger compartment. It is part of the heating ventilation and air conditioning (HVAC) system and seldom causes any trouble unless it has corroded from the inside out. This can be caused by coolant neglect or by electrolysis corrosion between the heater core and car body.

Some vehicles have suffered a high rate of heater core failures because the OEM heater cores didnt offer adequate corrosion protection. Some of these have been replaced under the factory warranty, but others that are out of warranty have created a good demand for aftermarket replacement heater cores.

A leaky heater core will often drip coolant onto the floor of the passenger compartment. Pressure testing the cooling system or the core will verify the need for replacement if it cant hold pressure.

Odor is another problem that may be blamed on the HVAC system. But the odor isnt coming from the heater core, it is coming from microbes growing on the evaporator core. Condensation on the cool surface of the evaporator creates a perfect environment for odor-causing microbes to multiply. Some evaporators have a special coating that is supposed to kill the unwanted bugs. But if odor is a problem, the inside of the HVAC system may have to be sprayed with a biocide to sterilize these parts.

Another replaced component is the cabin air filter on some late-model vehicles. Often located behind the glove box, at the base of the windshield or in the HVAC unit is a filter to trap dirt and odors before outside air enters the passenger compartment. The OEM-recommended replacement intervals on many of these filters is every 30,000 miles. Even so, its a good idea to inspect the filter yearly, especially if the vehicle is driven in a dusty environment or is exposed to a lot of urban pollution.

ANTIFREEZE
There seems to be a lot of confusion these days about which type of antifreeze is the "right" one for a customers vehicle. The right type is one specified by the vehicle manufacturer or one that is compatible with the OEM coolant and meets the OEM specifications.

There are several different types of antifreeze in use today. The "orange stuff" in General Motors vehicles is "Dex-Cool." It uses a totally different corrosion inhibiting chemistry so it should not be intermixed with ordinary "green" or "yellow" coolant. If the two are accidentally intermixed, it can reduce the corrosion protection of the long-life coolant from its normal 150,000 miles down to 30,000 miles.

Ford uses long-life coolant in a few of its models as do some of the Japanese and European auto makers. The best way to determine what type of antifreeze is recommended is to refer to the vehicle owners manual. There should also be an underhood decal indicating the type of coolant required.

LEAK SEALERS
Leak sealers are a popular DIY product because they can often postpone the need for cooling system repairs. But the chance of permanently sealing a leak goes down as the size of the leak goes up. Sealers are okay for minor pinhole leaks in radiators and heater cores and to stop seepage around expansion plugs or even minor porosity leaks in a cylinder head, block or head gasket. But sealers are usually a waste of time if a water pump or a hose is leaking, or the engine has a serious internal leak like a blown head gasket, cracked head or block.