Oil leak, but same compression in all cylinders

VEGARD EGGEBø

MEMBER
2007 MAZDA 5
1.8L
4 CYL
2WD
MANUAL
105,000 MILES

Hi, first off all I am kind of new to this subject and have my English excused.

I bought this car cheap and it has an oil leak.
When it is cold and reaching 3000 to 4000 rpm dark gray/black comes out of it.
It also smells a bit burnt after I have driven it.

Today I did a wet compression test.
Cylinder number four (left side on the engine) had a bit oil (guess it was oil) in it.
When I did the compression test I got 280 psi in all cylinders.
After I put some oil in it I got 310/max psi.

First off I thought it was the piston rings or valve seals, but should not it be at least a 15% gap between the cylinders?

Any other ideas about where the leak and the problem is?
Any help would be gladly appreciated.

3 Replies

MHPAUTOS

MECHANIC
31,938 POSTS

Those compression readings are very high! You did it as a key crank reading?

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Thursday, October 12th, 2017 AT 5:28 PM

VEGARD EGGEBø

MEMBER
2 POSTS

Tested it again and got 250 in all cylinders. Yeah, I did a normal reading.

I am a bit confused about this whole thing. The engine leaks some oil, but it still has good compression. And since there a little oil in one of the spark plugs, could it one of these problems?
Valve cover gasket, the seal upon the sparkplug on the valve cover gasket, head gasket, cracks or leaks in the main block?