By Larry Carley
Technical Editor
The hottest summer weather is almost upon us, so over the next couple of months you’ll likely see a surge in servicing cooling system parts such as thermostats, water pumps, hoses, radiators and radiator caps. The parts can fail during hot weather because many cooling systems today have very little reserve cooling capacity. If the cooling system has not been maintained (low coolant level or old worn-out coolant), or it has any problems (leaks, a weak radiator cap, clogged radiator, bad cooling fan, etc.), it doesn’t take much to make the engine run hot and overheat. And once that happens, steam pressure inside the cooling system may blow out a weak hose, a worn water pump seal or even an aging radiator that has weakened due to internal corrosion.
Many motorists assume that if their engine overheats, all they have to do is wait until the engine cools off, open the radiator cap or coolant reservoir cap, then pour in some more water and antifreeze (or premixed coolant). In some cases, that may be all that’s needed. But in most instances, the engine overheated because the coolant was low or there was a problem in the cooling system that caused the engine to run too hot.
COOLANT LEAKS
The most common cause of a low coolant level is usually a leak. There may be an external leak somewhere in the cooling system, such as a hose, the water pump shaft seal, or the radiator or heater core, or there may be an internal leak in the engine or intake manifold (a bad head gasket or intake manifold gasket, or a hairline crack in the cylinder head or block).
If the coolant is low and there are no obvious external signs of coolant leakage (no coolant dripping from the engine, water pump, radiator or hoses, or under the dash on the passenger side of the car from the heater core), the cooling system should be pressure tested to see if there is an internal leak. This requires a cooling system pressure tester that attaches to the opening for the radiator cap or coolant reservoir filler cap. The tester uses a little hand pump to apply pressure to the system, and a gauge shows if the system is holding pressure or not. A good system should hold the rated pressure on the radiator cap for at least five minutes. If the pressure drops, there’s an internal leak.
Internal coolant leaks can often be temporarily plugged by adding a can of cooling system sealer to the cooling system. But your customer should be warned that sealers can’t stop every kind of leak (such as coolant leaking past a worn water pump shaft seal, or pinholes or splits in old hoses). Head gasket and intake manifold gasket leaks are also difficult to seal, so the recommended repair is to replace the bad gasket. This can be very expensive, not because of the cost of the parts but because of the cost of labor. Replacing a leaky $40 intake manifold gasket on a GM 3.1L V6, for example, may cost an additional $400 to $600 in labor. With head gaskets, the labor costs are even higher ($800 to $1,500 or more!).
LEAKY WATER PUMPS
If a water pump is leaking, the old pump must be replaced. In addition to a new or remanufactured replacement water pump, your customer will also need antifreeze (full strength or pre-mixed), and possibly some new hoses and clamps, and maybe a new drive belt.
On some engines the water pump is relatively easy to get at and is fairly simple to change. But on others, such as many overhead cam four-cylinder engines, the water pump may be buried behind the timing belt and may require quite a bit of effort to replace.
When possible, it’s always a good idea to visually compare the old water pump to the replacement pump to make sure the new pump will fit. Compare the housings and bolt holes to make sure they all line up the same. Check the hose connections and fittings to make sure they are similar (some aftermarket pumps may have extra fittings, or the fittings may be in a slightly different location so the pump will fit a wider range of applications). Also compare the height of the shafts on both pumps to make sure they are identical. Finally, if the replacement pump does not include new gaskets or O-rings in the box, make sure you get these parts, too. Gasket sealer is usually recommended, and thread sealer may be required for some bolts that screw into the engine’s water jackets.
On high mileage engines where the water pump is located under the timing belt, it’s also a good idea to replace the timing belt at the same time. The recommended service interval for rubber timing belts on most older cars is 60,000 miles, and up to 100,000 miles on most newer cars. Replacing the timing belt at the recommended interval is extremely important on “interference” engines that don’t have enough clearance between the valves and pistons if the timing belt breaks. On these applications, a broken timing belt will usually bend one or more intake valves (which can be very expensive to fix because it requires removing and sometimes replacing the cylinder head).
If the engine has more than 60,000 miles on it, and it still has the original drive belt, you should recommend a new belt if the water pump is being changed. Serpentine belts can become glazed and noisy as they age. Also, the automatic tension needs to be checked to make sure it is still capable of maintaining proper belt tension. If there is any sign of belt flutter or belt noise when the engine is running, chances are it also needs a new automatic belt tensioner.
DON’T FORGET THE FAN CLUTCH
If the engine has a mechanical belt-driven fan with a fan clutch, you should also recommend a new fan clutch. Why? Because the service life of the fan clutch is about the same as the water pump. After 75,000 to 100,000 miles, the shear characteristics of the silicone fluid inside the clutch break down and allow too much slippage. This may prevent the cooling fan from turning fast enough to provide adequate cooling when the engine is working hard.
REPLACE THE THERMOSTAT
A new thermostat should be recommended if the engine overheated. Overheating often damages the thermostat by overextending the temperature-sensing wax-filled element that opens the thermostat. This may cause the wax inside to ooze out. The next time the vehicle is driven, the loss of wax may prevent the thermostat from fully opening — which increases the risk of the engine overheating again. So to minimize the risk of any further problems, it’s a good idea to simply replace the thermostat.
A thermostat is a relatively inexpensive item. The thermostat is usually located in a small housing on the engine where the upper radiator connects to the engine. But on some engines, it may be located elsewhere on the engine, or even where the lower radiator hose connects to the engine.
Many technicians recommend replacing the thermostat on a high mileage engine (over 100,000 miles) for preventive maintenance whether the thermostat is causing any problems or not. Their logic? It’s far cheaper to replace a thermostat than a head gasket or cylinder head. Overheating causes the cylinder head to swell, which often crushes the head gasket and caused it to leak. Overheating can also warp or crack the cylinder head, and may even cause an overhead camshaft to seize.
LEAKY RADIATORS
Leaky radiators can sometimes repaired, but it’s often faster, easier and even cheaper to replace the old radiator with a new one. Most cars today have aluminum radiators, which typically have a longer service life than the copper/brass radiators that were commonly used up until the 1980s. The lead solder in copper/brass radiators often corroded and allowed leaks to develop along the tube and header seams. Aluminum radiators have no lead solder and are not vulnerable to this type of corrosion. Even so, if the corrosion inhibitors in the coolant wear out, electrolytic corrosion can eat away at the inside of the radiator eventually causing it to fail. It’s the same story with heater cores. So if a radiator or heater core has failed from the inside out, it’s a waste of time to try to patch the leak. The radiator or heater core must be replaced.
Small cracks or pinholes in aluminum radiators can sometimes be repaired by carefully cleaning the damaged area and applying a high temperature epoxy designed for this purpose, or by using special aluminum solder. But such repairs are tricky, and the repair may not last. That’s why replacing the radiator is often the best repair option.
A replacement radiator should have the same cooling capacity as the original (or better). If a vehicle is used for towing, or the engine has been modified for more horsepower, a radiator with increased cooling capacity should be recommended to reduce the risk of overheating. Such applications may also benefit from a larger cooling fan, or installing an auxiliary electric cooling fan.
The height and width of the radiator, and the location of the hose fittings must match the original. The thickness, however, may vary depending on the design and efficiency of the new radiator. A thicker radiator typically provides increased cooling capacity, which a radiator with smaller tubes and more fins per inch usually provides higher cooling efficiency.
COOLANT CONFUSION
When an engine needs coolant for any reason (overheating, leaks or a coolant change), vehicle manufacturers recommend using the same type of antifreeze that is already in the vehicle’s cooling system for optimum corrosion protection. That means matching coolant colors and formulas for compatibility.
In recent years, coolant chemistry has changed a lot. The old two-year/30,000-mile green formula coolants have been replaced with long life organic acid technology (OAT) orange and yellow formula coolants that typically last for five years or 150,000 miles. These are long-life coolants that require less frequent changes, but they are NOT lifetime coolants. The corrosion inhibitors do eventually wear out, requiring the coolant to be changed to maintain proper corrosion protection — something which fewer and fewer motorists seem to do these days.
To minimize confusion over which type or color of coolant to use in a particular vehicle, many aftermarket coolant suppliers have consolidated their product lines and gone to a “global” or “universal” coolant which works in all makes and models. The basic issue has been the compatibility of these aftermarket coolant additive packages with the OEM coolant additive packages. Having one product to sell certainly simplifies your inventory requirements, and eliminates confusion about which product to sell a customer for their vehicle. But for those who want the exact same type of coolant as before, they can buy that too.
Pre-mixed coolant (antifreeze already mixed with water) is more convenient to use than full strength coolant because it eliminates the need for messy and sometimes inaccurate mixing. Full strength antifreeze must always be diluted with water (a 50/50 mix is the standard recommendation). Pre-mixed coolant also reduces the risk of contaminating the coolant with salts and minerals that can cause internal corrosion. Ordinary tap water contains a lot of dissolved minerals, and softened water contains chlorine. Only distilled or deionized water should be mixed with antifreeze. Pre-mixed coolant is also more profitable to sell than undiluted antifreeze on a per gallon basis. But customers need to know what they are buying (pre-mixed or full-strength undiluted antifreeze) so they do not accidentally dilute pre-mixed coolant by adding water.
