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Car Overheating This Summer Check Your Thermostat

By Ted I. Boatman

Most motorists think only of their car or truck’s thermostat only when it comes to getting winter heat out of their in-car heater. Yet not checking your radiator’s thermostat can result in engine overheating resulting in major auto repairs during the upcoming summer driving season. The thermostat (some motors use several) can cause overheating resulting in major engine damage and repair costs. Regardless of whether you are going to have extra demanding summertime driving via a summer vacation auto trip, pulling a boat or trailer behind your car, truck or Sports Utility Vehicle or simply tooling around town its best to have your radiator’s thermostat checked out. On top of that its relatively simple engine repair and testing work that you may be able to do yourself – to save costs.

Simply put the thermostat in your automobile’s cooling system can cause overheating by either failing to open or by not opening wide enough to allow coolant to circulate through the radiator heat exhaust system. The result can be as serious and costly to repair as a cracked engine block or head., extra carbon formation detonation, burned valves or bearing damages. Alternatively it may be a case of a cold running and over-cooling engine. Events may be that your engine is actually running on the cold side – that is actually too cool rather than at proper engine operating temperatures), which can directly result from a thermostat running in a stuck wide open position as opposed to the mechanism closing with lower coolant temperatures to restrict engine glycol coolant flow . As opposed to helping heat up the coolant liquid to more optimal temps everything runs stone cold. While most auto owners and even vehicle fleet maintenance managers don’t think of a vehicle’s powerplant running too cool as a bad thing overall this situation can result in damages and excessive engine and component wear & tear as well as premature engine failures from crankcase sludging , poor fuel vaporization as well as vital lubrication oil dilution. Not a good series of events for long term engine health and lifetimes.

The first rule when working with any auto cooling system is to let it cool down before working on it and certainly before you open the pressurized radiator cap. The second rule is know that simple glycol coolant is deadly to pets as well as wildlife. Clean up any ethylene glycol anti-freeze that spills or leaks promptly. Don’t leave it laying around on the concrete, roadway or your driveway it any spills or leaks.

Next take care when the thermostat is inspected to drain the system (save the coolant itself if clean), until the coolant level is below the thermostat housing. Remove or rinse the thermostat itself when the housing cap is off and the thermostat itself is removed.


Take care to carefully and fully inspect the internal workings of the unit once removed – that is the thermostat valve itself. Hold it against the light to determine how well the valve contacts the seat. A spot or two of light showing is not automatic cause for product rejection. However if light does show all around the valve discard the thermostat on the spot.

The test that most mechanics and auto shops use for thorough full testing is to check opening temperatures by suspending thermostats pellet part down in a container of water. The thermostat must be completely submerged and must not touch the container sides or bottom. It is most important for a full and accurate testing that a fully accurate thermometer be employed. Again in a similar manner the thermometer unit must not touch container sides or bottom.

Place the container over a source of heat and gradually raise the temperature of the water itself. Stir gently as the temp increases. The whole point of the test and the exercise is to carefully watch and record exactly at what point the valve begins to open. This should be within 5 to 10 degrees Fahrenheit (that is 2.8 to 5.6 degrees Celsius, plus or minus) of the temperature rating stamped on the thermostat itself or the box it came in.

Continue heating the water until the valve is fully opened and note the water temperatures again. It can be said that in general the thermostat should be wide open at a rating of about 20 to 24 degrees Fahrenheit ( that is 6.7 to 4.5 degrees Celsius) above opening temperatures.

Lastly if the unit is defective – it does you or your vehicle cooling system and engine no good what so ever. Defective thermostats are not repairable and on top of that are inexpensive to replace. Replace the unit with a proper new replacement.

Most drivers and motorists think little of their automobile’s thermostat come summer time and summer time driving. Yet by not checking this vital part of your car, truck or SUV’s cooling system you risk transportation breakdowns and potentially costly and preventable vehicle repair costs. Take the time to have your radiator and cooling system’s thermostat or thermostats checked out now – that is especially if you are planning a summer time vacation driving trip and especially if you are or will be hauling a trailer or boat trailer behind your vehicle.

About the Author: Ted I. Boatman

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