At 02:51 PM 5/14/2000 , you wrote:
>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'd take a close look at #6. It's low, could be your leaker.
>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
Higher the better Jack. Do you have, or had pinging problems? Ever towed
a real heavy load, or any load that put the hurt on the motor? I haven't
seen any cylinder pressures under 125 unless there was a serious problem,
on any engine I've seen. In your case, with the highest being 204, and
lowest 165, your near the edge of being out of the 25% pressure
differential limit. 204 does seem high, but could be normal, designed that
way to make more power for given cid.
Mike Schwall
__________________________
mschwall@flash.net
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