WHY IS THERE OIL ON TWO OF MY SPARK PLUGS HAS ...

  • Tiny
  • kennethmorrow
  • 1999 Mercury Cougar
  • 144,000 miles

Why is there oil on two of my spark plugs has really bad compression and is making a hissing sound

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Wednesday, October 24th, 2012 AT 1:27 AM

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  • Tiny
  • mhpautos
  • Expert
  • 30,598 posts

Oil on the plugs and low comps usually mean broken rings or a hole in the piston, get a leak down test done this will help pin point the problem.

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Wednesday, October 24th, 2012 AT 10:19 AM
  • Tiny
  • kennethmorrow
  • Member

What is a leak down test

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Wednesday, October 24th, 2012 AT 12:45 PM
  • Tiny
  • mhpautos
  • Expert
  • 30,598 posts

This is when you apply a low pressure compressed air into the cylinder at TDC with both valves closed, there is a special tool that screws into the spark plug hole, with the low pressure applied you can determine where the leaks are, such as valves, rings etc.

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Wednesday, October 24th, 2012 AT 7:44 PM
  • Tiny
  • kennethmorrow
  • Member

Can I do the leak down test myself or do I hav to take it to a shop

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Wednesday, October 24th, 2012 AT 8:03 PM
  • Tiny
  • mhpautos
  • Expert
  • 30,598 posts

You need the adaptor a compressor and a regulator to drop the air pressure down, to high a pressure will force the piston down and open a valve this will give you a false reading, if a manual transmission you can put it in gear and pull the hand brake on to help hold the engine at TDC.

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Wednesday, October 24th, 2012 AT 8:06 PM

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