exhaust fumes getting into the cooling system

I have a 97 Chevy Venture that was overheating. I had tried a few things (new thermostat, coolant refill, bled air from coolant system) so I took it to a mechanic. He told me that there were exhaust fumes
getting into the cooling system and that I needed to replace the head gaskets. Unfortunately, when I took the heads off I did not see any obvious problems with the gasket. I did find that the water returns in the heads were about 50% clogged with sludge (could be from radiator stop-leak that I used a few months ago). I am now worried that the gasket may not be the problem. What should I do now? Do I put it all back together with new gaskets and hope for the best? Is there anything else I can look for?
Thanks in advance, -Stephen Smith
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Clean them up real good an look real close for cracks, also check the block over good. Might have the heads magna-fluxed as well. BUT it doesn't take much of a leak to cause problems, especially on the newer engines.
--
Steve Williams



"Stephen" < snipped-for-privacy@yahoo.com> wrote in message
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"Stephen" wrote

I've never seen a head gasket on a Venture van (3400) leak combustion into the cooling system. Of course, I usually don't see extremely high mileage engines, so it is possible. Usually, the gaskets split and leak externally. The only other possiblity is a cracked head...again..rather rare on these engines.
I would have the heads checked for cracks and if nothing is found, throw it back together and see how she runs. Make sure there is nothing wrong with the water pump (again, very rare, about all that happens with these water pumps is that they leak) Perhaps you have something clogging the radiator, or condensor?
Ian
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Call a few machine shops, find one with a reasonible price on pressure testing cylinder heads. Have the heads pressure tested. If they pass, have them mill the deck surface to clean it up.
If you find you have a cracked head, get one from a salvage yard. Have it pressure tested before install. As well as milled.
Having the heads milled trues the gasket sealing surface. Not really an issue on 50K and less engines. Yet older, high milage engines can have slightly warped sealing surfaces.
You might also have your intake manifold sand blasted. Then look for cracks. If the Cross over is cracked next to a cooliant passage this could also cause the problem.
Charles
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The van does have about 100K miles on it. I should have mentioned that.
-Stephen Smith
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