General maintenance consists of things that should be done regardless of problem, and easy and obvious steps. Make the following observations while the vehicle is not hot or running. Note that these steps combined should take a few minutes, but they can save costly and embarrassing mis-diagnosis:
Coolant full?
Coolant mixture OK? Hydrometer reading ok, color ok, no oil in coolant?
Radiator deposits? Drain enough coolant to see some of the tube ends.
Radiator cap OK (no cracks and swelling)
Radiator has clean air flow path? Bugs? Leaves? Clogged air conditioning coils in front of it?
Radiator dented or otherwise obviously damaged?
Hoses OK? Feel them.
Coolant in oil? Yellow gunk on oil filler cap?
Water pump turns easily? Without excessive shaft play? Any signs of leakage?
Belts OK, with reasonable tension?
Evidence of freeze plug leaks?
Head gasket bolts appear loose?
Now some observations with the engine running:
Thermostat work? (detect increased pressure by squeezing hose, or observe coolant flow in a radiator drained of a few inches of coolant)
Heater work? Heater hoses hot?
Radiator flow? View flow after draining a few inches of coolant. More rigorous tests require removal of the radiator.
Bubbles? Look for bubbles or foam in the coolant in the radiator. If so, there might be a head gasket problem. The block tester or smog sniffer will tell.
Steam from exhaust? If so, suspect head gasket problem.
Pressure test OK?
Block tester or smog sniffer reveal combustion gasses in coolant?
I'm well aware that the combustion gas test has a significant cost attached to it, but I have still included it in General Maintenance. The cost of misdiagnosing a broken head gasket is so severe that I believe it warrants the combustion gas test in all but the most obvious cases. Even in cases where a definitive cause is found, such as a broken fan belt, remember that the overheat could have consequently broken the head gasket. Obviously, if steam out the exhaust or coolant in the oil reveals a broken head gasket, you know you have a broken head gasket without doing the combustion gas test.
The few minutes and dollars spent on these tests greatly increase the chance of an accurate diagnosis and estimate. Once again, remember that overheats are likely to cause consequential damage, some of which in and of themselves can cause overheats. It's therefore common for an overheat to be found to have multiple causes.
Good Luck
CJ
