compression test

Discussion in 'General Motoring' started by danielr, Feb 6, 2010.

  1. danielr

    danielr Guest

    I ride a 1997 SL SOHC, 185.000 Km, standard transmission.
    Oil is changed every 3500 Km, I use Castrol Synthetic 5W30, and K&N
    oil filter.
    I know; some of you might believe it is a waste of money; but I am a
    FIRM believer of preventive maintenance.
    I am VERY satisfied with this car.
    Which should be range (max / min) of values resulting in a compression
    test for this engine?
    Thanks in advance for your assitance.

    danielr, Feb 6, 2010
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  2. danielr

    Oppie Guest

    Rule of thumb is 125-150 psi depending on the compression ratio of the
    engine. Make the compression test with all plugs removed, the ignition coil
    disconnected and wide open throttle. Crank for 5 seconds to get a stable
    reading. Log readings, do all cylinders and then repeat. Make sure you get
    consistent readings on each cylinder. Readings between all cylinders should
    be within 5-10 psi. If you get a cylinder that reads low, put a couple of
    squirts of oil into the cylinder and repeat the test. If the reading comes
    up, most likely worn piston rings. If the reading stays low, could be head
    gasket or valves. Don't forget to label the plug wires as you remove them to
    make sure they all go back in the right places.
    Oppie, Feb 8, 2010
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  3. danielr

    Private Guest

    @278,000 km my 96 SOHC 5sp pumped to
    155 lbs dry and warm, and 230-270 lbs with oil added,
    (the 230 cylinders had less oil than the 270 ones.)

    Adding more oil will seal the rings better but will also raise the
    compression ratio, I should have measured the added oil better by counting
    the oil can squirts and adding the same number.

    Previous test @178,000 km pumped 130/128/131/130 warm and 128/126/128/125
    cool and 220/185/225/215 oiled warm and 190/155/185/185 oiled cool. The
    center cylinders were retested 1,000 km later both 160 psi warm. I suspect
    a piece of crud on valve in #2 cyl during first oiled test.

    YMMV depending on accuracy of your gauge, I think mine is OK and was top
    quality and quite expensive in its day but is about 35 yrs old. As Oppie
    topposted, your results are probably more important relative to each other
    cylinder after dry and wet testing, as these results will all be with the
    same tester. Record your results in your maintenance log and then you can
    compare them in another 50 or 100,000 km to detect any trends.

    Many mechanics will debate the value of compression testing and will often
    advocate for a cylinder leak down test as being a superior test, but a plain
    compression test is easier and uses simpler tools and will quickly find
    large problems like one bad cylinder or valve.

    Good luck, YMMV, make sure you have locked the throttle butterfly valve in
    open position for test, IMHO warm is best for reliable results and
    Private, Feb 8, 2010
  4. danielr

    danielr Guest

    Hi "Oppie"

    Thank you very much for your help.

    danielr, Feb 8, 2010
  5. danielr

    Oppie Guest

    And thank you 'Private' for your input also.
    Oppie, Feb 8, 2010
  6. danielr

    navaidstech Guest

    Let's see... I've got a 92 SL1 SOHC with 553,000 km on it. Been
    putting Castrol Synth in it and a cheap Motomaster oil filter since
    the car had 100,000 km on the odometer. I change my oil every 10,000
    Did a compression test about a month ago and got 185-190 PSI in all
    cylinders dry and cold. Didn't bother putting any oil in the cylinders
    to do further checks, since I was happy with the readings.
    Hope this helps!

    navaidstech, Feb 13, 2010
  7. danielr

    danielr Guest

    Thanks Alex;
    It certainly does, as it provides a reference to effectiveness of the
    same oil I'm using.
    Thank you very much.again
    danielr, Feb 14, 2010
  8. danielr

    navaidstech Guest

    No problem Daniel. Good luck!
    navaidstech, Feb 18, 2010
  9. danielr

    Private Guest

    You should be happy with these numbers and your service life. I would
    normally suggest verifying the compression test gauge but why tempt fate, if
    it aint broke, etc., it is the cylinder variation that is most important

    Looks like you got a good one, keep it as long as you can and don't fix
    anything that doesn't need opening up.

    Good luck.
    Private, Feb 22, 2010
  10. danielr

    navaidstech Guest

    Thanks for the words of encouragement.
    I intend to keep the car as long as I possibly can although it got
    really close to getting junked a couple of months ago.
    One of the timing chain guides has shattered leaving the chain
    rattling and car losing power. My wife was super happy as she wants me
    to get rid of the car and buy something "decent".... well, I stuck to
    my guns, ordered a new kit and replaced the chain, guides, sprockets,
    Now the car runs like new and my wife ain't very happy about that! LOL

    BTW... guys at work are having a tough time believing that the car
    being as old as it is (18+ years) still runs on the original clutch
    and the exhaust system (well, the muffler was replaced a few times,
    but everything else is original)

    navaidstech, Mar 12, 2010
  11. danielr

    Oppie Guest

    The Stainless Steel exhaust systems popular now (because of the acids in
    catalytic converter exhaust eating out steel pipes) go on just about
    forever. I used to have a Chrysler product that had 208K miles on the
    original pipes. As with you, muffler only had been replaced three times.
    Pipes were still good when we junked the rest of the car.
    Oppie, Mar 17, 2010
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