Question about checking compression

barrys · 01-16-2009, 08:15 PM

I want to check the compression on an engine before I pull it. Directions with the compression tester says to check it with a warm engine. I can't keep the engine running long enought to warm it up(it hasn't been run lately and was a farm beater truck). How different would the results be with a cold engine vs. a warm engine? I plan on selling the engine, it is in a truck that I bought for the frame, body is toast, engine was said to have been rebuilt. Thanks

bradrhale · 01-16-2009, 08:19 PM

it is kinda hard to sell an engine that you cant keep running. if you get a number that is way too low, no matter if cold or hot, than it is going to be bad. a cold cylinder should still be well above 100 psi.

chevyman125 · 01-16-2009, 08:33 PM

you should actuly tets it when it room temp. i work on sleds alot and when we test them we let them get to room temp and hold it wide open and pull it over to compression test it, i dunno if trucks are the same

mudseeker · 01-16-2009, 08:46 PM

engine close to operating temp, all plugs pulled, fuel and spark disabled and crank engine at WOT.

leolkfrm · 01-17-2009, 05:22 AM

I agree with Brad, but I would look for at least 125 for a fairly fresh engine broke in.
Is it an old carb version with a block fuel pump? run a gas can line to the pump and see if it will warm up, if it has been sitting for a long period the lifters may be colapsed till pressure gets to them, how is the pressure when you crank it?

barrys · 01-18-2009, 10:07 AM

They all read 145-165 cold.

stumpuller454 · 01-18-2009, 10:13 AM

Good to go!

barrys · 01-20-2009, 02:09 PM

Quote:

Originally Posted by bradrhale

it is kinda hard to sell an engine that you cant keep running. if you get a number that is way too low, no matter if cold or hot, than it is going to be bad. a cold cylinder should still be well above 100 psi.

It ran great when I got the truck, gas was at least 1.5 years old and it was 25 degrees. I know the engine can run good, I just wanted to check the compression, figure if I know it is good, it is a better selling point.

01-16-2009, 08:15 PM	#1
barrys Full Member Join Date: Jan 2008 Location: Norristown pa Posts: 28	Question about checking compression I want to check the compression on an engine before I pull it. Directions with the compression tester says to check it with a warm engine. I can't keep the engine running long enought to warm it up(it hasn't been run lately and was a farm beater truck). How different would the results be with a cold engine vs. a warm engine? I plan on selling the engine, it is in a truck that I bought for the frame, body is toast, engine was said to have been rebuilt. Thanks

01-17-2009, 05:22 AM	#5
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 4,931	I agree with Brad, but I would look for at least 125 for a fairly fresh engine broke in. Is it an old carb version with a block fuel pump? run a gas can line to the pump and see if it will warm up, if it has been sitting for a long period the lifters may be colapsed till pressure gets to them, how is the pressure when you crank it? __________________ 4 wheels move the body 2 wheels move the soul B.W.A.I

01-18-2009, 10:13 AM	#7
stumpuller454 Senior Member Join Date: Dec 2007 Location: Grande Prairie, AB Posts: 2,206	Good to go! __________________ SUPERCHARGED 454 K2500 GMC! Watch My Youtube Videos!!<<<

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01-16-2009, 08:19 PM	#2
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 9,547	it is kinda hard to sell an engine that you cant keep running. if you get a number that is way too low, no matter if cold or hot, than it is going to be bad. a cold cylinder should still be well above 100 psi.

01-16-2009, 08:33 PM	#3
chevyman125 Full Member Join Date: Jan 2009 Posts: 31	you should actuly tets it when it room temp. i work on sleds alot and when we test them we let them get to room temp and hold it wide open and pull it over to compression test it, i dunno if trucks are the same

01-16-2009, 08:46 PM	#4
mudseeker Senior Moderator Join Date: Feb 2006 Location: michigan Posts: 7,155	engine close to operating temp, all plugs pulled, fuel and spark disabled and crank engine at WOT.

01-18-2009, 10:07 AM	#6
barrys Full Member Join Date: Jan 2008 Location: Norristown pa Posts: 28	They all read 145-165 cold.