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    Repeat Overheat? – Free Tips from an ASE Master Tech

    Coolant Pressure Test KitDennisB © Summary: An overheating engine should NOT be ignored. A repeat overheat condition can cause more serious problems such as a blown head gasket which can be very costly to repair. It’s obviously best to avoid the vehicle overheating multiple times, because the chance of doing serious damage increases each time it’s been ran hot. Checking the coolant level is the first thing to check, on a car suspected of overheating. *Caution – never remove the radiator cap on a hot engine. Just visually check the coolant overflow bottle which are usually plastic and somewhat see-through. It’s important to know that even some overflow bottles (reservoirs) hold pressure and therefore the pressurized cap shouldn’t be removed on these either while the system is hot. Steam abruptly escaping can cause some serious burn injuries. If the cooling system is low, the next thing to do when the car is cool, is to fill the system and pressure test the system with a coolant pressure test kit. An adapter fits where the coolant cap normally goes and the system can be pressurized with an attached pump. It’s always good to perform a visual inspection during this time. Look underneath the car for drips or a stream of coolant. Trace the leak back to the source of the problem. If the leak is not obvious, look for corrosion that may have built up from a slow leak. Look at all heater hoses, radiator hoses, the radiator itself and find the water pump weep hole – more on this and some how to tips below.

    Check the car or truck for coolant leaks. I know it’s a cliché but, an ounce of prevention is far better than a pound of cure.

    The heart of the cooling system is the water pump. Going with this analogy, the coolant is the lifeblood. OK enough of this analogy stuff. The water pump is a common source of a coolant leak. There are usually two weep holes in a water pump. The top one provides a vent which allows any moisture to evaporate rather than trapping it. Trapped moisture can cause bearing corrosion resulting in failure. A noise is typically heard when water pump bearings fail. It is normal for a very small amount of coolant to seep past the shaft seal and out the bottom weep hole. This lubricates the seal extending its life. However, if there’s an actual drip the water pump needs to be replaced. On a car I worked on before, I saw a small wooden dowel inside the weep hole to stop a leak. One customer once told me what he truly thought; “Those darn water pump manufacturers put those holes in there on purpose.” He thought that they were designed to fail, which is simply not true. If the hole is plugged, the bearing will soon fail due to water causing it to rust. Water pumps can corrode from within for other reasons as well. The impeller can rust to a point where it can no longer pump coolant. This can be caused by poor maintenance and/or electrolysis eating away at the metal. The water pump gasket is also sometimes a source of a coolant leak. Some water pumps are located behind timing belt covers an cannot be inspected easily. Due to the harder access, it’s a good idea to replace the water pump during timing belt servicing on higher mileage cars. Also if a water pump leaks coolant on a timing belt, it can be weakened and should also be replaced during water pump replacement.

    Other sources of coolant leaks. Obviously if a leak occurs anywhere, the cooling system will not work as designed. The heat normally transfers from the engine to the coolant which is then pumped and cooled off in the radiator. Then the cycle repeats itself. If the coolant is not full, there will not be enough cooling capacity to keep the engine from overheating. Leaks can occur anywhere coolant circulates. The radiator, water pump, hoses, heater core, engine block, head or multiple gaskets in between. Pressure testing the entire cooling system is the best place to start if a leak is not obvious but is suspected. Coolant or radiator caps shouldn’t be forgotten, since they are usually taken off when pressurizing the cooling system for pressure testing. And block testing for carbon (exhaust) in the cooling system is a good way to check for internal leaks; Which may indicate a blown head gasket, or extreme cases a cracked head or block. If you have a repeat overheat, I definitely recommend performing this test. If exhaust is in the cooling system, the coolant will be pushed out. Usually it will be forced out of the overflow reservoir. Continuous bubbles rising in the radiator can also be a sign that there’s an internal exhaust leak.

    The thermostat helps the engine reach operating temperature quickly. It does this by restricting the flow of coolant until the temperature quickly rises to its normal operating temperature. A thermostat that sticks in the closed position can cause an extremely fast overheat condition. A malfunctioning thermostat which is stuck in the closed position, stops coolant from circulating so it’s just as bad as having no coolant in the system at all. The spring is designed to open the thermostat when it reaches a certain temperature. When I worked at Carmax, we would routinely have to show extended warranty inspectors sent by aftermarket warranty companies, that a thermostat had failed by heating them up in a large coffee cup using a heating element which is normally used to heat water for tea or coffee. With a thermometer in the cup, the thermostat can be tested to see if it will open at the correct temperature. The spring’s temperament can be altered if a car is severely overheated. That’s why it’s often recommended to replace the thermostat if an overheat of any kind occurs in addition to whatever else had failed. A thermostat that opens too soon or is the wrong temperature rating can cause a code to be set by the vehicle’s computer. So never install the incorrect temperature t-stat. Stick with the original temperature thermostat that was installed at the factory. The computer self tests depend upon that being correct.

    Radiators cool off the antifreeze before it’s returned to cool the engine by circulating inside of it; then the heat is transferred to the coolant and carried away. Pressure testing is an excellent way to find leaks in a radiator, They sometimes leak at the seams and other times from the cooling tubes. Occasionally the neck where the radiator cap goes can leak. Radiators can not only just leak, they can also get plugged up (or restricted). In the 80’s we used to remove the radiators and have them “rodded”. Sort of angioplasty for the tubes that make up the radiator. I know I said I wouldn’t continue this analogy. Anyway, this clears the passages to restore circulation and cooling capacity. Nowadays, the supply of low-cost radiators made in China has put most radiator shops out of business. — Next Page »

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