Question: I loaned my car to my brother for a few days and when he returned it he told me it was overheating and I should get it fixed right away. I hadn鈥檛 noticed anything like this previously. What could be causing this?
A.T.
Answer: This will be difficult without more details. I鈥檓 curious what your brother observed to lead him to say this and what actions he took to protect the car from damage. Normal engine operating temperature for most cars and trucks is about 195聽degrees F, with occasional increases to perhaps 230 degrees. Perhaps he observed a higher than normal reading? Anything over 240 would get my heart beating faster.
If there鈥檚 a red coolant light that鈥檚 illuminating, this is a really big deal as the threshold for lighting is likely 250 degrees, seriously hot. Also, if the car is spewing coolant on the ground, emitting steam, or making gurgling sounds from under the hood, it鈥檚 screaming: 鈥淔ix me right now!鈥�
Here come the questions: When does the higher than normal temperature occur, at low speeds, or at higher speeds? Is the car a front-wheel drive vehicle with a transverse (sideways) engine? If so, it would use an electric cooling fan to draw air through the radiator as conditions warrant (fluctuations in temperature between 195 and 230聽degrees are normal when it is stopped or operating at speed as the fan cycles on and off). If you have an older car or pickup truck with a longitudinal engine, it would likely have a mechanical fan driven by the engine (you won鈥檛 see temperature swings at idle as the fan runs all the time).
If higher than normal engine temperatures are encountered mostly at low speeds in an electric-fan vehicle, an inoperative fan is a likely cause. If overheating occurs mostly at high engine load with a mechanical fan, the fan clutch may be faulty. Overheating at all or higher speeds (both fan types) can have many causes: low coolant level, faulty water pump impeller, sticky thermostat, collapsing radiator hose, missing/damaged air diverter, among others.
Checking the coolant level would be an important first step to begin assessment of this condition. Be sure to only do this with the engine cool, as hot and pressurized coolant can cause serious burns when a radiator cap is removed or a hose bursts. Some vehicles use an overflow tank (thin plastic with loose-fitting cap) and the radiator cap is on the radiator, while others use a thick-walled expansion tank with a pressure relief cap on top. Checking fluid level in only an overflow tank is not sufficient, as the radiator could still be low (it鈥檚 OK with an expansion tank). If the coolant level is low and there are no signs of rapid leakage, it鈥檚 OK to add water temporarily and seek nearby professional services right away. If there鈥檚 rapid leakage, a tow is best.
Overheating an engine can cause serious damage and is to be avoided at all costs. Please make every effort to get this to a shop as soon as possible for a complete diagnosis. With luck, perhaps the fault could be as simple as a leaky hose or loose hose fitting.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers can email him at [email protected].
