My car started to run a little hot the last time out and I found that the coolant level was 3+ quarts low since last checked about 800 miles ago. I found no leaks but noticed a little white smoke coming from the tailpipe. I warmed up the engine, pulled the plugs, and did a compression test. The results were 150 to 160 psi on all cylinders. When looking at the plugs I noticed #5 was very clean compared to the rest (third plug from left). Note that the engine had just come off of choke so it was very rich. This is all leading me to believe that I have a cracked head, possibly in the intake port. Is this common? The engine has 109k miles and has never been apart. I will do a cooling system leak test soon.
With the engine cool, pressure test the cooling system. If it holds pressure, then do it again with the engine at operating temperature. Let it warm up with the pressure cap removed. If it still holds pressure the engine most likely does not have an internal leak. You can double check this with a test kit that detects exhaust gasses in the cooling system. Important! If the cooling system does not hold pressure - do not attempt to start it (the engine) until you remove the plugs.; if coolant is leaking into a cylinder you could get a hydraulic lock, which will ruin your whole day.
Thanks for the advice, John. I did just that last night, pressuring the system to 16 psi at 9pm. This morning at 8am the system pressure was 14psi. To my surprise there was a pool of about one tablespoon of coolant on top of the timing cover. Tracing the leak path I found a very small leak at the upper radiator hose. The clamp was snug, but not tight. I tightened the hose clamp and repressurized the system to 16 psi. So far no drop in pressure. Evidently the leak was so small that the coolant burned off without a trace and didn't leak when sitting unpressurized. I got lucky this time.
