Automotive Cooling System
Automotive Cooling System Topics
  1. Are molded radiator hoses better than flex hoses?
  2. What is the best way to fix a coolant leak?
  3. What kind of maintenance is recommended for the cooling system?
  4. How often should belts and hoses be replaced?
  5. What can make an engine overheat?
Flexible hoses are the one-size-fits-all variety. Available in various diameters and lengths, flexible hoses can be bent to fit a wide range of applications.

Molded hose is like original equipment hose in that the hose is molded to fit a specific application. This simplifies installation and gives a perfect fit (though some molded hoses do have to be trimmed to length prior to installation).

Regardless of the type of radiator hose your customer wants, do not forget to recommend new clamps. Original equipment spring-type clamps lose tension with age and may not seal the hose properly. Worm-type clamps are much stronger and easier to install.

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What is the best way to fix a coolant leak?
Proper repair depends where the leak is. Coolant leaks often occur at the water pump shaft seal. Other leak points include radiator, heater cores, hoses, freeze plugs, and the engine itself.

Small radiator leaks, as well as minor internal seepage inside the engine or past a freeze plug, can often be temporarily plugged with a can of sealer. No sealer will plug a leaky water pump, hose or badly damaged or corroded radiator. The only cure is to replace the faulty component.

Small radiator leaks can often be patched by soldering or using a special high-temperature epoxy. Other options include sending the radiator to a specialty shop for repair or recoring, or replacing the entire radiator itself with a new one. With a leaky heater core, replacement is the best option.

Internal coolant leaks are more of a challenge to fix because they require more expertise to diagnose and repair.

Coolant can seep past a head gasket or hairline cracks in the engine block or cylinder head and enter the combustion chamber or crankcase.

If not stopped, such a leak can cause major damage to piston rings, cylinders and bearings, as well as overheating due to coolant loss.

An internal leak may be indicated if the cooling system is losing coolant without obvious leaks. The first item to check is the radiator cap. A weak cap that can't hold pressure will allow the system to boil over. Both the cap and radiator should be pressure checked with a pressure tester.

If the cooling system fails to hold pressure, coolant is leaking internally. The question is where? A compression check on the engine will tell if a head gasket is leaking or if there's a hairline crack in the cylinder or head.

A higher than normal dipstick level and/or excessive moisture in the crankcase would indicate a coolant leak into the crankcase. In either case, major engine work will be necessary to repair the leak.

Another type of internal leak is one that can occur between the coolant and automatic transmission fluid (ATF). On most vehicles with automatic transmissions, ATF is routed through an oil cooler inside the radiator.

If the tubing leaks, coolant can enter the transmission lines, contaminate the fluid and ruin the transmission. Red or brown drops of oil in the coolant would be a symptom of such a leak.

Because the oil cooler is inside the radiator, the radiator must be replaced to eliminate the problem. Transmission fluid should also be changed.

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What kind of maintenance is recommended for the cooling system?
Replacing coolant on a regular basis will prolong the life of the radiator and other cooling system components. Most new car maintenance schedules call for coolant changes every three years or 50,000 miles. Many professional mechanics consider that too long and recommend every two years or 24,000 miles. There are some who argue that annual coolant changes on late model vehicles with bimetal engines (aluminum heads/iron blocks) and/or aluminum radiators is a good idea.

It does not really make much difference how often the coolant is changed as long as it is changed before losing its corrosion resistance. Antifreeze is made of ethylene glycol (which never wears out) and various additives (which do wear out).

Some additives provide "reserve alkalinity" to neutralize internal corrosion before it can start. As long as the coolant is changed before its reserve alkalinity is depleted, the cooling system should be no worse for the wear. If you wait too long, the result can be expensive internal corrosion in the radiator, heater core and engine.

How can you tell when it is time to change the coolant? The only way to know if the coolant still has adequate corrosion protection is to test it. By dipping a test strip in the coolant and noting its color change, you can determine coolant condition and whether or not it is time to replace it.

Vol. %
Boiling Point
F(at 0 psig)
Point F

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How often should belts and hoses be replaced?
Most hose manufacturers recommend replacing hoses every four years. V-belts should be replaced every three years or 36,000 miles. The incidence of failure rises sharply after the fourth year of service for hoses and third year for belts.

The lifespan of a typical serpentine belt is about five years or 50,000 miles. Serpentine belts are thinner and more flexible than V-belts. They run cooler and last longer, but cost about twice as much to replace.

The hard part is convincing customers to change belts and hoses as preventative maintenance BEFORE they fail. Few people do, yet they could save themselves a lot of unnecessary grief and expense if they would.

Rubber hoses deteriorate with age. Tiny cracks develop in the rubber which eventually cause hoses to split, blister or leak. Oil contamination and atmospheric ozone can accelerate the process.

Engine vibration and motion can cause hoses to wear if they are too short or rub against other parts. This applies to fuel, vacuum and emission hoses as well as coolant hoses.

A visual inspection will often uncover bad hoses. Pinching hoses to check for age cracks, brittleness or mushiness can also help locate hoses that need to be changed.

However, neither technique will reveal all the hoses that might need replacing because hoses wear as much from the inside out as they do from the outside in. A hose that appears okay on the outside may actually be on the verge of failure because of internal deterioration.

According to research done by one hose manufacturer, internal corrosion caused by electrochemical degradation is the primary cause of cooling system hose failure. The coolant acts like an electrolyte and allows a current to flow between engine and radiator. This causes micro-cracks to form inside the hose which eventually leads to pinhole leaks and weakening of hose fibers.

With belts, heat and mileage are the main causes of wear. Every time a belt passes around a pulley, it bends and flexes. This produces heat which hardens the rubber over time. The wear process is greatly accelerated if the belt is loose and slips.

The additional friction between belt and pulley will make a belt run hotter. After millions of journeys around the pulleys, even the best drive belt begins to suffer the effects of age. Rubber begins to crack and fray and the internal cords become weak and brittle.

You cannot always determine a belt's true condition by appearances alone. Any belt obviously cracked and frayed should be replaced. With many of today's bandless belts, there is no outside cover to peel loose and betray the belt's deteriorated condition.

A belt may appear to be like new on the outside, yet be on the verge of failure because of weakened separated cords inside.

When a belt is replaced, it is important that the belt be properly tensioned. If too loose, it will slip and wear quickly. If too tight, it may damage internal cords as well as overload shaft bearings on accessories it drives.

The rule of thumb about tightening a belt until there is about half an inch of give between the two furthest pulleys is not always accurate. A belt gauge" that measures actual tension is the only sure way to know if a belt is tensioned properly.

Because a V-belt normally takes a set after a few minutes of running, one set of tension specs may be provided for new belts and another for used belts. Any V-belt that has been run for more than 15 minutes should be considered a used belt.

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What can make an engine overheat?
Overheating is caused by anything that leads to a loss of coolant, prevents the cooling system from getting rid of heat, or causes excess heat in the engine itself:

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