Identifying The Causes of Overheating

Some overheating problems aren't related to the cooling system at all. Other circumstances that can cause a vehicle to overheat include lack of oil, a blown head gasket, and transmission problems. If the cooling system seems to be in good order after you check it and do the maintenance work in this chapter, investigate these possibilities :

  • Late timing : If you haven't tuned and timed your engine recently, late timing may be causing it to overheat by making the spark plugs fire the fuel/air mixture after the piston moves back down from the top of its stroke. When the spark plugs fire too late to allow all the gases to burn properly, more heat burdens your cooling system. Late timing alone doesn't cause a car to overheat by more than a few degrees, but coupled with other problems, it can bring the engine temperature to a critical point. The remedy is simple: Just check your timing and adjust it.

  • Plugged radiator : Some radiators get so plugged up with rust, sediment, or small insects that even cleaning and flushing them doesn't get all the junk out. Because plugged passages cut down on the system's liquid circulation, the system can't cool efficiently. The remedy is to have a radiator specialist remove and steam clean the radiator.

  • Slipping fan belt : Check the fan belt or accessory belt that drives the water pump to be sure that there's no more than about X inch of give. If the belt is looser than that, it may not be driving the pump properly, and that can impair circulation and overheat the cooling system. If your fan belt seems loose or very frayed, replace it.

  • Collapsing bottom radiator hose : Occasionally, a bottom radiator hose begins to collapse under the vacuum that the water pump creates, and the impaired circulation causes overheating. Here's how to check the hose: If your car starts to overheat, park safely and open the hood without shutting off the engine. Make sure that the car is in Park with the parking brake on. Then take a look at the bottom hose (be careful not to get your hair or clothing caught in the fan or the fan belt) and see whether the hose has collapsed. If it has, replace it.

  • Low oil level : If you still can't find the cause of overheating, check your oil dipstick. A vehicle that's low on oil tends to overheat because the oil removes from 75 to 80 percent of the "waste heat" in your engine (in
    addition to doing its other job of cushioning the moving engine parts). If you're 1 quart low in oil and your vehicle holds 5 quarts, the oil can carry away 20 percent less heat (the oil cools off in the crankcase).