Sorry, been busy. I'm a little confused by your post above.
Now the first test you did was a pressure check of the cooling system right? You lost 0.5psi after 5 minutes at 15psi. I wouldn't call this much of a leak. Might even be considered normal. Could even be your test fixture leaking. This test says to me that your cooling system is sealing fairly good....move on.
2nd & 3rd test you call a combustion leak test. Are you monitoring crankcase pressure here? Or are you still hooked up to the cooling system and looking for leaks from combustion chamber to the cooling system?
Also, please tell us what location you are monitoring the pressure at. i.e. where did you hook up to?
