First of all, hello all, first time poster, so bear with... I have a 5.3 engine with a cooling problem. It started off by just a mystery leak somewhere. Not a bad leak, just a couple of quarts every month or so. This has progressed into an overheating issue. I was a gradual thing, slight overheating then cooling down and running normal for a while. It has progressed to where it spikes after just a couple of miles. Here is what I have done so far: Thermostat (tried running with and without just in case it was a bad replacement part) Check oil - no coolant pressure test - 10 minutes at 18psi with no loss. Flushed radiator Talked very nice to engine, asking it to please behave Talked not so nice, threatening very unpleasant things if it not behave Any ideas?