I've removed the intake manifold on my 89 Suburban 5.7L, 96k mi, to try and fix a coolant leak. Coolant is disappearing from the cooling system and showing up in the oil (about 1qt/3000mi).
Last year I changed the intake manifold gasket for similar reasons. At that time it was leaking coolant out the top manifold on the right front part of engine. The gasket replacement fixed that leak. I used a FelPro gasket along with permatex Hylomar HPF sealant. I used the Permatex goop to hold the gasket in place while I installed the intake manifold. The permatex was worthless in that regard. The gaskets were not perfectly flat. They would lift and slip out of place before I could get the manifold on. Instead I used a drill bit through the bolt holes to position the gasket once I had the manifold in place. I'm wondering if the Hylomar sealant prevented the gaskets from sealing properly? They sure were easy to remove.
I probably was leaking coolant into the oil before the first repair. I din't pay attention because as I was losing coolant, I could see it appearing on top of the engine (no, it was not leaking from the thermostat. It was definitely from the intake manifold/head gasket.)
What do y'all recommend for holding the gaskets in place during manifold positioning? Something that will _positively_ seal around the coolant passages. Or should I install the FelPro gaskets dry? Both the heads and manifold are clean and dry so the gaskets should stck fine, if that's how they're designed to work. Or should I go with a different brand?
I was going to take out the plugs in the bottom of the manifold and reseal them. They are in _tight_! There was no sign of leakage around them so I left them alone.
Everything is all cleaned up and ready to reassemble. I could find no obvious sign of leakage when I took the manifold off. It's kinda hard to tell though since some coolant spills out when the manifold is popped loose. 1qt or two qts every 3k miles (~ 100 hours) is a pretty slow leak, but it's enough to thin the oil. Oil pressure dropped quite a bit between changes (from 20psi to 10 psi at idle). If this manifold gasket replacement doesn't fix it I'll try some stop-leak. I'm crossing my fingers the leak isn't deeper down in the motor.
-RC
R.Clarke spam snipped-for-privacy@BlocKmindspring.com RTP, NC, USA