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Originally Posted by springgeyser
TDC doesn't matter with a compression test. A leakdown test is done at TDC.
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You're wrong. You don't position the engine at TDC, that's true, but you have to crank the engine long enough for the cylinder to go through an entire intake/compression cycle (and hence TDC after the compression stroke) to get a value that means anything. You don't develop any cylinder pressure on the intake stroke before compression, or on TDC after the exhaust stroke before the next intake cycle.
2-3 seconds isn't long enough, period. Do it at least 7 seconds and I can almost guarantee you that's where the 185 to 205 variance came from.
If you truly have compression in the cooling system, you have some breech between combustion gases and coolant, period. As I've mentioned I have yet to see this except as the result of improper assembly or some kind of cylinder/head damage. t-stat and rad cap shouldn't matter when it comes to a "false boil". I would do a leakdown and pressure test the cooling system and try and figure out where the coolant is going by sight or sound.