Mechanics

MERCURY COUGAR PISTON PROBLEM

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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Kennethmorrow
October 24, 2012.



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.

Mhpautos
Oct 24, 2012.
What is a leak down test

Tiny
Kennethmorrow
Oct 24, 2012.
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.

Mhpautos
Oct 24, 2012.
Can I do the leak down test myself or do I hav to take it to a shop

Tiny
Kennethmorrow
Oct 24, 2012.
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.

Mhpautos
Oct 24, 2012.