Cooling System Diagnosis

An overheating car can make anyone hot under the collar. The old cliché "heat kills" especially applies to engines: high temperatures make hoses and gaskets brittle, can cause cylinder heads to distort, and create other unhappy problems. Granted, some heat is needed during start-up to burn off condensation that accumulates while the vehicle isn't running (which explains thermostats, EGR valves, and such). But once the vehicle is warmed up, excessive heat becomes the engine's archrival.


Cooling systems operate at a specific pressure. This raises the coolant's boiling point. When the system's intended pressure is exceeded, the spring in the radiator cap is designed to retract, allowing coolant to pass into the overflow "puke" tank and pressure to be relieved. When too much coolant bypasses into the overflow tank, boil-over occurs.

Inspection The old cliché "heat kills" especially applies to engines.
The cooling system is largely an out-of-sight, out-of-mind scenario: Most drivers ignore it until the temperature gauge goes into the red, the car overheats or won't start in the winter, or a green puddle forms on the garage floor. But just as tire pressure and oil level should be checked regularly, the cooling system needs periodic attention.


After every oil-dipstick inspection, give the cooling system a glance. Look for cracks or bulges in the heater and radiator hoses, especially near the clamps (see Tip 8). Hose clamps should be snug enough to seal the hose to the metal or plastic nipple, but not so tight that the metal band cuts into the rubber. Also look for signs of chaffing anywhere a hose touches or comes close to a metal or moving part.


Next, eyeball the coolant's color. Depending on the vehicle manufacturer's recommendation, the coolant should be neon green, pink or orange. The photo above shows a truck that had no antifreeze in the system, only water. Rust formed, a leak sprung, and the fan liberally dispersed the iron-oxide-color fluid over the engine compartment and front suspension. Which brings us to the subject of leaks.