Trying to do a leak test, I found a product to buy at advance.

But came to wonder what could be the difference in this case: if I crank the engine with the compression tester gauge on, it would hold about 180 psi.
If I just leave it there without pressure relief for about 5 minutes, it equals that I put 180 psi on the cylinder with a leak down tester.

What kind of logic am I missing?

p.s. I'm trying to find if I have head gasket leak between the gasket and the coolant passages.
I have no milky residue, no oil, but exhaust smell in oil dipstick, bubbles coming up without the level dropping, and sweet smell only at cold start.
Overheat once about two months ago, not again so far. Changed radiator recently, was having coolant steaming out of reservoir. The symptoms calmed down after I bled it.

 

What ever happened to people searching ? found the answer in under 5 seconds http://autos.yahoo.com/maintain/repa...ques057_1.html

 

If you have bubbles coming up in your coolant you have a blown HG or a cracked sleeve or something similar.

The purpose of the leakdown test is to tell you where youre losing compression. The compression test just tells you that youre losing compression.