Keeping that engine cool!
by Jim Kerr

Late summer heat, hard working equipment, and an engine that has had a couple years of service. All these conditions add up to the possibility of cooling system failure. While usually overlooked unless there is a problem, regular cooling system maintenance can save you the stress of a rushed repair and perhaps even save your engine!

Your truck, tractor, combine, or any other water cooled equipment are all subject to wear and tear on their cooling system. Hoses are the most common failure. The rubber hoses harden with age and heat and begin to crack where they flex near their connections. A simple visual inspection should locate cracked hoses. Don't take a chance; replace them.

Less common problems include hoses that have deteriorated internally. The inner lining of the hose can separate and block the coolant flow. Check for restricted coolant flow by feeling along the hose and noting any changes in temperature. A change indicates a restriction. This test also works for locating a restricted radiator. Move your hand over the surface of the radiator noting sudden temperature changes. Caution, it may be very hot! You may have to temporarily disable the fan so you can safely touch the radiator.

Lower radiator hoses pose a special problem. They may look good and seem fine at low engine speeds, but they can be sucked shut by the water pump suction at higher engine speeds. Most lower radiator hoses have a wire coil inside them or are wire reinforced to prevent them collapsing, but the wire may have rusted and fallen apart. Squeeze the lower radiator hose. It should be firm and well reinforced. A soft spongy hose can cause hard to locate heating problems.

Leaks are not only annoying, but can also decrease the efficiency of the cooling system. Almost all modern cooling systems operate under pressure to raise the boiling point of the coolant and to prevent cavitation at the water pump inlet. Raising the system pressure by one pound pressure increases the boiling point by 3.25 degrees F. Most systems use a pressure cap on the radiator rated between 15 and 18 psi. Combine the increased pressure with the higher boiling point of an antifreeze/ water mixture and the engine coolant shouldn't boil under any normal operating conditions. Check the radiator cap seals and replace it if there is any doubt.

Leaks at fittings and gaskets will leave stains around them. A careful look at all fittings and block frost plugs should pinpoint small leaks. Radiators that are beginning to leak will have green fuzzy corrosion around the leak. Usually radiators start to leak where the tubes enter the tanks at the corners. Vibration is the culprit here! Once a radiator has started to leak where the tubes enter the tanks, it must be removed for a recore. When installing the rebuilt radiator, make sure all rubber mounts and isolators are in place. If a radiator mount comes loose during operation, repair it immediately to save your radiator.

Thermostats are installed to maintain minimum cooling system operation. They can't prevent an engine from overheating! Thermostats can stick open or shut, and the only option is to replace them. A thermostat rated at 180 degrees F should start to open about 15 degrees before that and be fully open by 180 degrees. Leaving the thermostat out will actually cause the engine to overheat. The thermostat also acts as a restriction to coolant flow so the coolant will have time to absorb heat in the engine block and dissipate it in the radiator. Some heavy duty vehicles use dual thermostats to increase coolant flow in large cooling systems.

Antifreeze if the lifeblood of your cooling system. Unfortunately it doesn't last a lifetime. Two years is the usual service interval. After that time, the anti-corrosion additives and water pump lubrication additives have worn out. Water pump lubrication additives can be found among many parts department chemical supplies, but changing the antifreeze may still be required. An unusual but effective method of testing the anti-corrosion ability of the antifreeze is to measure it with a voltmeter!

A simple digital voltmeter can be bought for only a few dollars and has a multitude of uses. Worn out antifreeze can act like an electrolyte in a battery and uses up metal engine parts as part of its chemical reaction. Test the antifreeze by placing one lead in the coolant and the other lead on the engine. If the meter shows a voltage reading, then the antifreeze should be changed. I have seen engines that have tested over 2 volts and the frost plugs are virtually eaten out of the block!

When installing new antifreeze, make sure you are using the correct type. Diesel engines require low silicate type antifreeze; the label will say compatible for diesel engines. Using the wrong antifreeze may cause erosion and cavitation of cylinder sleeves and will require expensive repairs later.

Mix the antifreeze with water according to the manufacturer's instructions for maximum cooling system protection. Most are mixed 50/50 but some are to be mixed 60/40. Check that label! Many repair shops use an antifreeze recycler because the cost of disposing used antifreeze in an environmentally friendly way has increased sharply. Salvage that old used coolant by taking it in to be recycled. The machine filters the coolant, and then the acidity is tested. Depending upon the acidity level, an additive package is selected and mixed with the coolant. Recycling is cheaper than buying new antifreeze, protects our environment, and produces coolant that protects as well as new.

A relatively new organic based antifreeze has been used in General Motors vehicles since 1996. Called DexCool, it has a five year life span and is suitable for use any vehicle. If you are switching, flush the cooling system completely with water first. Mixing regular antifreeze with DexCool shortens its life back to the regular two years!

Airflow through the radiator is critical to proper cooling. Duct work and fan shrouds are designed to direct the airflow correctly. Rubber seals are also used to prevent air from leaking through the wrong way, and they are often overlooked. That gasket along the front of the hood on your truck directs the air through the radiator. If you see any gaps, sealing them will help the cooling system.

Bug screens help keep the radiator fins from becoming plugged with bugs but they can also stop up to 40% of the airflow through the radiator. If it is necessary to use a bug screen, select one with as large as openings as possible.

The space between auxiliary oil coolers, air conditioning condensors and radiators is usually at a minimum and can easily catch enough leaves, straw, or chaff to hinder proper cooling. Wash the fins out frequently but be careful with high pressure washers! Too close with the washer nozzle and you will find lots of fins flattened out. It can take hours to straighten them but is much easier if you use a special "fin" comb available from most tool suppliers.

Finally, even though everything is in fine shape, there are days when the cooling system operates near its top temperature limits. An auxiliary electric cooling fan may be the answer. A salvaged electric fan from an old front wheel drive car may be the cheap way to go but most of these fans are designed to pull the air through the radiator and have to be mounted behind it. Usually there is little extra room there. A better bet is to buy a "pusher" fan designed for hot rods and race cars and mount it in front of the radiator. These kits have the added benefit of including a temperature switch that mounts to the radiator hose to control fan operation. Make your own mounting brackets for the fan rather than use the plastic mounting straps that push through the radiator fins. These plastic straps can loosen and vibrate enough to wear through the radiator tubes!

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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