Compression Test
Junior User
Joined: Nov 2007
Posts: 83
Likes: 0
All things being equal, warm or cold makes no difference. Rings and valves are designed to seal at all temps.
Try doing a comp test and a hot engine and get all the plugs out fast enough and with out burning the crap out ya hands or arms. I have done 100000's of test, and when the %'s are with in spec, the engine is fine.. I prefer cold
Try doing a comp test and a hot engine and get all the plugs out fast enough and with out burning the crap out ya hands or arms. I have done 100000's of test, and when the %'s are with in spec, the engine is fine.. I prefer cold
Laughing Gas
Joined: Aug 2003
Posts: 1,175
Likes: 9
From: So. Cal.
Well, I'd agree, I wouldn't want to be pulling the plugs from a 4.0L V-6 when it's hot, although the engine we're talking about is an I-4. And I sure wouldn't want to argue with someone who had done hundreds of thousands of compression tests. Gosh, you must be 70 years old, and have done eight compression tests a day for the last 50 years! Thats a lot of experience!
Laughing Gas
Joined: Aug 2003
Posts: 1,175
Likes: 9
From: So. Cal.
I believe that your experience with race engines has colored your opinion. In the world of the daily driver with dirty oil, worn pistons, tapered & out-of-round cylinders, stuck rings or worn ring grooves, oil blow-by, carboned up combustion chambers, and leaking valve guides, the engine temperature WILL make a difference in compression tests. And although I haven't done nearly as many compression tests as you, I have seen all of the above. I believe that the engineers who wrote the shop manuals for our vehicles know a lot more than we do when they specify a hot engine for a compression test.
If it's impractical to do the test in the hot condition, then that fact should be considered when evaluating the results of your cold test. A hot test will likely give higher compression readings & better consistancy.
If it's impractical to do the test in the hot condition, then that fact should be considered when evaluating the results of your cold test. A hot test will likely give higher compression readings & better consistancy.
Junior User
Joined: Nov 2007
Posts: 83
Likes: 0
Temp will not make a variance difference, and thats what a compression test does. It test all cylinders and gives a base line to the condition of all of them. A set engineers design will say 200PSI is a good broke in engine with great ring seal and great valve seal.
but if every one of them says 188 then the given atmosphere conditions dictate thats the max that day and time. Put the heat to the engine and do it again and you may only get 170 or 212 out of it..
But if all are with in a % then everything A OK>
Thats all I got to say about that. I will post no more about it. I got better things to do.
but if every one of them says 188 then the given atmosphere conditions dictate thats the max that day and time. Put the heat to the engine and do it again and you may only get 170 or 212 out of it..
But if all are with in a % then everything A OK>
Thats all I got to say about that. I will post no more about it. I got better things to do.
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