An engine that runs consistently hot causes premature aging …whether you notice any classic signs of overheating or not. Consequently, scheduled cooling system maintenance takes on huge importance. and your routine maintenance should much more than a flush-in-fill occasionally. Excessively high temperatures can cause engine knock, which shortens the life of virtually all key engine parts, including pistons, pins, crankshaft and bearings. High temperatures also increase friction (and engine wear) by thinning out engine oil and causing parts to warp, affecting engine sealing.
Make sure you’ve really filled the system. Many late-model cooling systems are prone to trapping air, which not only reduces heater output, but can create harmful hot spots in the engine.
If the car manufacturer has a specific bleeding procedure, including the opening of air bleeder valves on the engine block or cylinder head, be sure to follow it when you fill up. If the radiator cap is not the highest point of the cooling system, jack up the front of the car and raise it, which helps it self-bleed.
Make sure the reservoir is filled to the proper marked level, and recheck the level periodically.
Check the clutch fan on a north-south engine. Most accurate: Measure the air temperature when the clutch locks up. Slip the probe of a pyrometer (temperature-measuring meter) into the fan shroud and run the engine until it warms up. When the engine is warm, the fan should virtually lock up. Fan noise will increase noticeably and you can note the temperature on the meter which should be between 150° and 170°F.
No pyrometer? Try to spin the fan with the engine fully warmed up (but not running). If it turns easily, the clutch is bad. Also, run a finger around the bearing area at the rear of the clutch assembly. If it picks up a blob of goo, that’s silicone, and it indicates a leak from the clutch assembly. Unbolting the clutch fan assembly and installing a replacement is a straightforward job.
Test the electric fan, or fans for the radiator. At least one fan should begin turning within a minute of turning on the air conditioner. Check your car’s owners manual to see when a second fan and/or the high-speed range of a single fan should come on.
Blocking the front of the radiator or air conditioner condenser with cardboard is sometimes necessary to raise coolant temperatures high enough to fully check a multispeed fan system.
The fan shroud can sometimes become loose or may be missing alltogether. If either is the case, the fan’s efficiency drops dramatically. Removing the thermostat is NOT the answer. Doing so won’t cure overheating (unless the thermostat is defective and malfunctioning) and it doesn’t allow the engine to warmup properly. Cold starts are responsible for most engine wear… occurring until the engine becomes warm. Cars without thermostats may never warm up fully – confusing the computer into running in it’s overly rich warmup mode forever.
Look under the front of the car. Many modern cars draw in cooling air from the underneath. If an air dam or chin spoiler is missing, the car may run too hot, particularly in highway operation. Cars with limited grille area may use underbody airflow, and cooling problems occur if they’re missing.