> I'm about to pull the valve covers >and attempt a head bolt re-torque,
but I'd really appreciate it if
>somebody could tell me the most obvious places to look to identify a
>cracked head.
Hi Michael,
So you see exhaust bubbling in your coolant tank? I would not start with
the valve covers. Nor would I pressurize the cooling system to find the
leak. Pull the plugs and do a visual inspection on them and into the
cylinders. The plugs may tell you the story; I imagine one seeing
coolant would be cleaner than those that aren't even with just a short
rinse. Peering into the cylinders may be enough for you to find the
leak. While exhaust was getting into the cooling jacket somewhere, water
likely seeped back in after shut-down.
If the visual inspection is not conclusive, I would pressurize the
cylinders one at a time to find the leak. On a V6 you have to be careful
about rotation; you don't want to loose your cam timing and crash valves
on top of other problems. So the process has to involve turning the
engine over in the normal direction of rotation (with the starter unless
you have the tools) until you get the cylinder you want to check near
bottom dead center. I would use a thin dowel rod down through the spark
plug hole, resting on the piston as an indicator. Once you get close on
one, you can make a mark and more quickly find others. Additionally, you
can probe cylinders that look close and reduce the amount of
starter-bumping needed to get each one individually to bottom. Anyhow,
once there, use an adapter to take the cylinder to maybe 75 PSI. A
leaker may be audible and of course you can watch for bubbles. Keep
track of which cylinders produce significant leaks and hope they are in
adjoining cylinders. If you have never done this before, you may be
surprised by the leakage possible in a seemingly tight engine.
I have done this with a adapter purchased at CarQuest, my tire air bottle
and a bunch of trips to the local gas station for air refills. Nice to
have a leak down tester and compressor but not necessary.
Not the guessing kind but finding two adjacent significant leakers
indicates to me the head gasket is the issue. I am not intimate with
fire rings; its usually either replacement time or a different issue. I
would be real surprised if re-torquing does anything to stop a water
leak.
At any rate, when you think you have found the problem, pull that head.
A clean trace between the cylinder and water jacket on either the head
or block will point to the problem if the engine was run for any amount
of time. Let the block drain for a while before you pull the head and
you may find all the evidence you need with just a visual inspection. If
not obvious, a close inspection with a straight edge and a bright
flashlight and maybe even a magnifier should do the trick. If that
doesn't work, I will be surprised. Pegasus Racing sells UV crack
detection supplies but at that point you might want to leave it to your
machinist anyhow.
Sure, you can freeze the engine enough to break a head. Would surprise me
though.
Let us know,
Scott Shure85' GTV6
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