Compression test - Hot or Cold?

[77SceptreOB]

Ok SeaCraft mechanics, Should you perform a compression test when the motor is Hot or Cold? Also what does the throttle position have to do with the reading?

[caper]

I prefer warmed up, but either will do. When the engine is warm all components are at operating temperarure and have expanded as designed.Throttle should be wide open to allow cylinders to suck air in. If throttle is closed test will show lower result because of restriction.

[bilgerat]

what he said, warm and wide open

[gofastsandman]

all plugs out

[Ed]

Engine should be warm, throttle wide open, all plugs out and neutral safety switch disconnected. Make sure you have a fully charged battery.

[Dogbomb]

Also, no smoking, no ignition sources anywhere close by, and always
have a cold beer at the ready to extinguish stray flames.

[Bigshrimpin]

It's a good idea to disconnect the fuel source and run the engine until it's out of any remaining fuel. I use one of these to ground the plug wires.

http://www.ebay.com/itm/350939409893

I've seen someone leave all 6 plugs dangling out while fuel mist sprayed out of the 5 cylinders. Let's just say I'm glad there was a fire extinguisher close by.

[Capt Terry]

Might be a good idea to remove the compression tester while engine is still warm. Probably not an issue on a water cooled engine, but almost couldn't get the tester removed from an air cooled VW after the engine cooled down. The thermal coefficient of expansion for aluminum (if I recall correctly w/o looking it up) is almost twice that of steel at the same temperature. So upon cool down the thread fit will get tighter. Fortunately the thread diameter is small, therefore it would be worse on a larger thread size.

[DonV]

Originally Posted by Dogbomb

Also, no smoking, no ignition sources anywhere close by, and always
have a cold beer at the ready to extinguish stray flames.

Blasphemy!!! You must have meant to say, have a cold water ready to extinguish the flames !!!