Cooling Off: Cooling System Parts and Service

Cooling Off: Cooling System Parts and Service

Cooling system service is an absolute “must-do” on any import nameplate. Once a cooling system suffers long-term neglect, it turns into an on-going source of problems for the owner and his servicing technician because, when corrosion starts to take place, the effects can’t be reversed. For that single reason, it’s important to sell your customers a “complete cooling system service.”

Furthermore, according to AAA, cooling system failures are one of the leading causes of vehicle breakdowns on the highway. Yet most of these breakdowns can be prevented by preventive maintenance. This includes:

Checking the coolant level regularly;

Checking the concentration of the coolant;

Checking the condition of the coolant;

Checking for leaks;

Changing conventional coolants every two years or 30,000 miles, or extended-life coolants every five years or 150,000 miles;

Inspecting belts and hose; and

Replacing any parts that are found to be leaking or failing.

Among these items, coolant leaks probably cause more problems than anything else. Most vehicles today have very little reserve cooling capacity. Radiators and coolant capacities have been shrunken to reduce weight (which helps fuel economy) and cost.

Consequently, most vehicles can’t tolerate a coolant leak for very long before the engine starts to overheat. Overheating leads to boil over and even more loss of coolant. It may also cause engine damage as parts swell up from the heat and start to seize and gall. Valve guides can be damaged, pistons can scuff, cylinder heads can crack and head gaskets can be crushed and fail as a result of overheating.

Overheating can also occur if the thermostat or water pump fails. The thermostat is a temperature-sensitive valve that regulates the operating temperature of the engine. It speeds engine warm up after a cold start and regulates the flow of coolant between the engine and radiator once the engine reaches normal temperature. The thermostat is usually located in a housing where the upper radiator hose connects to the engine.

The water pump is the heart of the cooling system. The pump’s job is to keep the coolant circulating between the engine and radiator. A paddle-style impeller is mounted on a shaft inside the pump housing. The rotating impeller pulls coolant in through the pump inlet from the lower radiator hose and pushes it on to the engine block through the pump outlet.

The pump shaft is supported by a bearing assembly and is driven by either a V-belt or serpentine belt on the front of the engine, or by the timing belt. A seal on the pump shaft prevents coolant from leaking out of the pump. Some pumps have a removable cover on the back, while others mate directly to a cavity on the engine block. Pump housings are usually made out of cast iron or aluminum, but some are stamped steel.

Water pumps move a lot of coolant – hundreds of gallons per hour, mile after mile. The pump shaft and bearings are under constant load, not only from the drive belt or timing belt, but also the fan on vehicles with pump-mounted mechanical cooling fans. Eventually the water pump bearings and seal wear out, and the pump begins to leak.

If a water pump is leaking, coolant will come out of the weep hole under the pump shaft. A tiny amount of leakage is normal, but a constant drip or stream of coolant is not. A leaky pump should be replaced as soon as possible to reduce the loss of coolant and the risk of overheating.

Another reason for replacing the water pump is if the shaft shows any visible wobble or the bearings are making noise.

Most original equipment water pumps last 60,000 miles or more, but a water pump can fail prematurely as a result of coolant contamination and cooling system corrosion. If the coolant is not maintained and replaced periodically, the corrosion-inhibitors eventually break down. Once this happens, rust and scale begin to attack the pump and everything else in the cooling system. These hard abrasive particles will ruin the pump seal and bearings. Symptoms of a pump failure caused by coolant contamination include rusty-appearing coolant seeping out of the pump shaft weep hole and hard calcium deposits around the hole.

During water pump replacements, technicians should thoroughly clean and flush the cooling system to remove contaminants. Cleaning with a chemical cleaner is especially important if the system contains rust and sediment. The cooling system and radiator cap should also be inspected and pressure tested to check for leaks. The system can then be refilled with a 50/50 mixture of distilled water and the type of antifreeze recommended by the vehicle manufacturer.

If a vehicle has a pump-mounted mechanical fan with a fan clutch, recommend a new fan clutch pump. A slipping fan clutch will reduce radiator cooling and may cause the engine to overheat.

A new thermostat should also be recommended if the engine overheated as a result of the water pump failing. Excessive heat will often damage the thermostat.

All of the hoses should also be inspected when the water pump is replaced, and any that are cracked, bulging, mushy or leaking should be replaced. New clamps should be installed with new hoses.

The radiator’s job is to cool the coolant. Air flowing through the radiator carries away heat and lowers the temperature of the coolant by a hundred degrees or more.

To cool efficiently, the radiator must be clean, in good condition and receive adequate air flow. The radiator’s front-mounted location ensures good air flow when the vehicle is in motion, but at low speeds and when the vehicle is stopped, a cooling fan must be used to boost air flow.

If a vehicle has air conditioning, a second heat exchanger called a “condenser” is usually mounted in front of the radiator. The condenser cools the refrigerant after it leaves the A/C compressor. The heat given off by the condenser when the A/C is on makes it harder for the radiator to do its job, so the cooling fan usually remains on all the time while the A/C is running.

Radiators can usually go eight to 10 years or more without requiring any repairs. But their frontal location makes them vulnerable to damage by stones and other road hazards. They can also become clogged with dirt and debris. In cold climates, road salt can also attack the metal causing corrosion that may eventually cause the radiator to leak. But the most common cause of radiator failure is internal corrosion caused by coolant neglect. If the coolant isn’t changed at the recommended service intervals, it may become acidic and attack the radiator.

The plastic end tanks on late-model vehicles can sometimes be damaged by steam erosion. The underlying cause is usually a low coolant level, which may be due to coolant leaks or a bad radiator cap that doesn’t hold its rated pressure.

Too much pressure inside the cooling system can also damage a radiator by blowing out the seam along an end tank. The cause is often a leaky head gasket that allows combustion gases to escape into the cooling system. The wrong radiator cap (too high a pressure rating) can do the same thing.

And did we mention freezing as yet another possible cause of radiator failure? If the concentration of the antifreeze in the coolant isn’t strong enough during cold weather to prevent freezing, the coolant may turn to ice, expand and rupture the radiator.

If a radiator is leaking, it must be repaired or replaced to stop the loss of coolant. Even a tiny leak that seeps only a few drops a day will eventually allow enough coolant loss to make the engine overheat.

Cooling system sealer products can be added to a leaky system and will usually stop small leaks temporarily. But the only permanent fix is to replace the leaky component. If the leak is in the radiator, that means a new radiator. If the leak is in a hose, that means a new hose. If the leak is at the water pump, that means a new water pump.

When buying a replacement radiator, the most important considerations are sizing the radiator correctly and making sure the inlet and outlet fittings are in the right locations so the hoses will line up the same way as before. The height and width are the most critical dimensions so the radiator will fit properly. Some replacement radiators may be somewhat thicker or thinner than the original, but as long as it provides the same degree of cooling (or better) than the original, it will work fine.

Other items your customer’s vehicle will probably need include a new radiator cap (make sure the pressure rating is the same as the original), antifreeze, and new upper and lower radiator hoses (and clamps). If the vehicle is more than six years old and/or has overheated, you should also recommend replacing the thermostat.

Selling antifreeze these days almost takes a degree in chemistry. Coolants today come in various colors and formulations. There are “conventional” coolants (the familiar “green” antifreeze that’s typically good for two years or 30,000 miles) and a variety of long-life coolants that are usually rated for five years or 150,000 miles. The color really doesn’t mean much because it’s just dye. It’s what’s in the chemistry of the product that counts.

Some types of coolants are formulated for specific vehicle applications or engine types (such as aluminum engines or bimetal engines with iron blocks and aluminum heads). Some vehicle manufacturers have very specific preferences when it comes to the types of corrosion inhibitors they use. The North American OEMs like one kind of chemistry, the Asian OEMS like another and the Europeans have their own ideas about what works best. That’s why there’s so much confusion about what kind of antifreeze to use.

The aftermarket, on the other hand, is great at coming up with ways to consolidate the mishmash of OEM requirements. There are now “universal” coolants that can be used in any year, make or model of vehicle. These are single-formula, long-life coolants that are compatible with both traditional antifreeze and the newer OEM long-life coolants.

Most vehicle manufacturers caution against mixing different types of coolants because of differences in the corrosion inhibitors. The issue is chemical compatibility. Most long-life antifreeze contains “Organic Acid Technology” (OAT) corrosion inhibitors to extend the life of the coolant. OAT inhibitors include a variety of different substances, so formulas will vary somewhat from one supplier to another.

Most conventional antifreezes, by comparison, contain silicates to protect aluminum, and also phosphates, nitrates and borates to inhibit rust and corrosion. Over time, these protective additives are gradually consumed. This decreases the reserve alkalinity (pH) of the coolant and eventually increases the risk of corrosion when the coolant turns acidic.

If a cooling system that contains an OAT-based, long-life antifreeze is topped off with ordinary antifreeze, it may shorten the service life of the entire batch of coolant to that of ordinary antifreeze. It’s difficult to predict how much of an effect this will actually have on the coolant’s longevity because it depends on the condition of the original coolant, the overall capacity of the cooling system and how much ordinary coolant is added to the system.

Intermixing different types of coolants won’t make the engine overheat or the cooling system self-destruct. But it may reduce the service life of a long-life coolant.

What happens if the cooling system in an older vehicle with ordinary coolant is topped off with a long-life coolant? Nothing. It won’t shorten the life of the ordinary coolant because it’s not formulated to go more than a couple of years anyway.

Another choice your customers face is whether or not they should buy concentrated antifreeze or a jug of pre-mixed antifreeze that already contains water. The latter is cheaper and easier to use. Antifreeze should always be mixed in equal portions with water when it’s added to the coolant reservoir or radiator. A 50/50 mixture will prevent freezing down to -34° F and prevent boilover during extreme operating conditions.

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