Compression test engine - cadillac deville 63
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The Classic Cadillac Forum Discussion, Compression test engine - cadillac deville 63 in Past Cadillac Vehicle Discussion; Hi, Sorry for my easy language. Does anybody know about how many PSI should be on compression test for very ...
  1. #1
    Dzida is offline Cadillac Owners Member
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    Compression test engine - cadillac deville 63

    Hi,

    Sorry for my easy language.
    Does anybody know about how many PSI should be on compression test for very good condition engine Cadillac Deville 64' 6.4L 6392CC 390Cu?
    What value is very good, when good, when is bad, etc.


    Thank You for all answer.

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  3. #2
    carnut is offline Cadillac Owners Master
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    Re: Compression test engine - cadillac deville 63

    As long as all cylinders are above 100 and within 10% of each other, they're OK. When they are 20% or below each other, then there's a problem internally. Best to do a dry test first on a warm engine then a wet test after that. A "wet" test is squirting a small amount of oil into each cylinder before doing the compression test. If the wet test improves the reading then you probably have weak, worn piston rings. All plugs removed, throttle fully opened is the proper procedure. If the dry test is OK, then a wet test might not be necessary!

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    Dzida is offline Cadillac Owners Member
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    Re: Compression test engine - cadillac deville 63

    Thank You very much for response.
    So only more than 100 PSI mean that copression is good? Cadillac has big engine and I thought that maybe compression should be also higher than for example "regular" smaller engine.

  5. #4
    carnut is offline Cadillac Owners Master
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    Re: Compression test engine - cadillac deville 63

    The engine size does not matter, the compression rating does however. My statement of "over 100" is a general guide. Your concern is do all of them read about the same within 10%?

  6. #5
    Jaykeane is offline Cadillac Owners Member
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    Re: Compression test engine - cadillac deville 63

    You'll also want to hold the throttle to the floor during the test, best to wire the throttle open so you're not pumping raw fuel into the intake via the accelerator pump. Above poster is spot on.. it's not a number thing.. it's a percentage thing..

    if you had say.. 84,80,87,84,88,40,86 and 82.. your issue would be the 40..
    Every gauge is different, none are NASA calibrated.. like the Light-Dark knob on the toaster on your kitchen counter..

  7. #6
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    Jeff R is offline Cadillac Owners Fanatic
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    Re: Compression test engine - cadillac deville 63

    If you have one that is low, blow some shop air in the cylinder and see where it is coming from. If you hear it blowing out the carb then intake valve. Out the tail pipe then exhaust valve. You'll have to find top dead center but it is worth a check. Sometimes a piece of carbon,etc will keep a valve from closing and running it a bit will clear it out.

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