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Head gasket or.......?

d1981

NAXJA Forum User
Location
Redding CA
Hi All,
New to this forum so I apologize if this has been covered somewhere else. I searched but couldn't find an answer(I know, not an excuse).

Anyways, I just got a 89 4.0l cherokee and only three cylinders are firing. After doing a compression check this is what I got:

Cylinder - PSI
1 125
2 90
3 85
4 0
5 85
6 124

So my question is this: Is this a typical reading for a blown head gasket or does this indicate more trouble than just a bad gasket?

I'm also noticing that the engine heats up rather quickly and the overflow bottle boils over after a couple minutes of idling. There doesn't appear to be water in the crankcase and there isn't any white smoke from the tailpipe either.
 
With low compression in cylinders 2, 3, and 5, and no compression at all in cylinder 4, you've got a serious enough problem that warrants pulling the head to find out what it is. Burnt valves could be one possibility, worn piston rings could be another, but cylinder 4 must have a hole in the piston.
Don't even bother with the leakdown test. Just pull the head.
 
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