Common Radiator and Cooling-System Problems

If steam is pouring from under your hood, a temperature warning light is glowing bright red on your dashboard or the needle in the temperature gauge is cozying up to the High mark, it's time to pull off the road and shut down the engine before it fries from overheating.

Any indication of overheating is a serious matter, so the best course of action is to shut down the engine to prevent further damage. Driving a car with an overheated engine can warp cylinder heads and damage internal engine parts such as valves, camshafts and pistons.

Even letting the engine cool for an hour and topping off the radiator with a 50-50 mix of antifreeze and water may not fix what's wrong. Here are some reasons an engine will overheat:

• The coolant level could be extremely low, because of long-term neglect or because a leak has developed in the radiator or radiator hoses. Coolant circulates inside the engine block to cool it, and the leak might be in the block, or from the water pump or heater hoses. Old coolant loses its corrosion-inhibiting properties, allowing rust to form and ultimately causing damage.
• The thermostat that allows coolant to circulate may be stuck in the closed position or a clog may have developed, perhaps from debris in the cooling system.
• The engine cooling fan has stopped working or the radiator's cooling fins are clogged with debris so that the air flow that reduces the coolant temperature is restricted.
• The radiator cap has gone bad and no longer maintains enough pressure in the cooling system, allowing coolant to boil over (engines normally operate at about 210 to 220 degrees Fahrenheit).
• The head gasket that seals the gap between the cylinder head and engine block may have failed, allowing coolant to leak inside the combustion chambers. The steam should be visible coming out of the exhaust system.
• The water pump has stopped working or the belt that drives it broke or is slipping and not pumping enough coolant.
• You've been towing a 5,000-pound trailer with a vehicle equipped to tow only 2,000 pounds, exceeding the vehicle's cooling capacity. (You probably also strained the transmission.)

Checking your engine coolant level in the overflow tank on a regular basis can help avoid disasters. If you have to keep topping off the coolant, that's an indication of a small leak that should be taken care of before it becomes a major one. Having your coolant tested and the entire system inspected by a mechanic every couple of years is an even better way to prevent cooling system disasters.