Leakdown Test Question

Discussion in 'Technical Q&A' started by spider348, Jan 18, 2004.

  1. spider348

    spider348 Formula 3
    Silver Subscribed

    Nov 3, 2003
    Full Name:
    Planned to do a leakdown test on my 348. All the cams are off etc, in the midst of a major service.
    I was told a leakdown test on a stone cold motor would yield no useful information. The motor must be warm.
    Curious why a cold motor would not yield valid info. Opinions?
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  3. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    Full Name:
    I assume warm so you are looking at/working with operating clearance, not something else.
  4. beast

    beast F1 Veteran

    May 31, 2003
    Lewisville, TX
    Full Name:
    Rob Guess
    A leakdown test is a test of overall sealing ability of your piston, rings, head gasket and valves. The ideal test would be done on a engine at operating temp.

    If you do test the engine cold more than likely you will find that you have more blow by the piston rings since the pistons have not expanded up. Does this make for a meaningless test??? Not at all rule of thubm should still be max of 10% leakage on any given cylinder. if the leakage is more than that locate the source of the leakage (out of crankcase breather if past rings, Intake or Exhaust for the valves.) If the leakage is past the rings squirt a some oil into the cylinder rotate the engine around about 20 revolutions and test it again. If the leakage is less that is a sign that the rings are worn or the engine has been in storage for a long time and the oil has washed off of the cylinder walls.


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