[Huskymaniac]

Originally Posted by 92 SVX

To be honest in my personal experience it does sound like the first signs of a blown head gasket.
The combustion pressure is slipping into the cooling passages (very very slight though at this point) it is displacing the coolant to the overflow tank since its only a very small amount at this point it isn't enough to push it out of the overflow tank yet. and why it passes the pressure test the combustion pressure is pushing from the cylinder to the cooling system and its very high pressures, pressurizing the cooling is (at this time) actually pushing the gasket into place sealing it better.

And since the problem is very very slight right now the car won't over heat until enough coolant is removed from the system to be low on fluid.

The last part makes perfect sense. What confuses me is that there is no oil in the coolant. Also, why doesn't the air get pushed into the overflow tank and coolant sucked back in when everything cools? To see what I am seeing, exhaust would need to get into the system and push coolant into the overflow and little to no coolant get sucked back into the radiator when everything cools.