I just finished a compression test on an '87 Dakota 3.9L V-6 and got the
follow results:
#1 197 psi
#2 184 psi
#3 195 psi
#4 190 psi
#5 204 psi
#6 165 psi
First off, the results seems high across the board. Haynes manual says
at least 100 psi and no more than 25% variations between cylinders.
Technically speaking, the above results are within the parameters for
normal readings. The two cylinders with the lowest reading are adjacent.
The crux here is that I am dead certain that the engine is leaking
combustion gases on the power stroke from one or more of the cylinders
into the coolant system and that coolant is leaking into one or more of
the cylinder chambers on the intake stroke. The reasons that I am
convinced of this is:
#1 The engine looses coolant with no evidence of an external leak.
#2 After running to warm up and then cooling down, the coolant in the
reservoir reeks of gasoline.
#3 The pressure at the upper radiator hose feels abnormally high. After
running awhile and then shutting down, the high pressure forces coolant
up through the rad cap and into the reservoir tank.
#4 After warm up, with radiator cap off, I see bubbles in the filler
neck after slightly revving the engine.
#5 After running for a while, the temp gauge fluctuates between hot and
normal as coolant is lost and circulation becomes erratic.
I have decided to remove both heads and have them rebuilt or exchange
them for rebuilts. In preparation for this, I bought a pressure tester
to do a static compression test and got the results posted above. I can
easily modify it and perform a leakdown test as well, but that will have
to wait until next weekend.
Can anyone comment on the readings that I got? Do they seem high? Any
and all comments welcome.
Thanks, Jack
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