Re: Compression testing, hot or cold?
Of course it's impossible to do a warm compression test on an engine that won't start!<br /><br />Compression tests and leak down tests are methods to determine why your engine is losing pressure in the cylinder, where that pressure is going, and how much compression you are losing. They are diagnosis for determining why your engine is running less than optimally, if the engine internals are worn, and if it is time for a rebuild in order to prevent more expensive engine damage on down the line. These tests can tell you exactly where the problem is before you tear the engine down. But to do them right, you have to do them warm. <br /><br />Compression and leak down tests are not the first place to go when an outboard won't start. Several other things would normally be checked first. If you are trying to diagnose a "no-start" problem using compression and leak down testing then you would have to do it cold, and hopefully you have already eliminated all other possibilities. An engine can run for a long time in a sad state of affairs on poor compression. They will generally start, however poorly they run.<br /><br />I understood the original poster's outboard did run, and that he did a cold check. If the engine runs, he should do a hot check.<br /><br />ob, I agree with the last part in your last post......except that if when doing the warm compression test, one cylinder comes up to 150 psi and the other stays at 120 psi.