did a cold pressure test today. 40 minutes and lost half of ONE psi ,,, so that is basically nothing in my book.... also did a cylinder leak test ( pumping shop air in the cylinder at top dead center, then i put the coolant pressure tester on the radiator, and did NOT pump it up. then i looked at the gauge on the rad. and was looking for an increase in pressure while there was shop air being blown into cyl. i checked all 4... NO increase in the radiator, so my guess is that i have a SMALL HAIRLINE crack in the head which only leaks when its hot. im not going to worry about it, the temp gauge does not fluctuate and it does not over heat...