Coolant in Exhaust Port **NFC**

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San Jose Steve
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Coolant in Exhaust Port **NFC**

Post by San Jose Steve » Thu Sep 06, 2018 12:44 pm

After a 400 mile R/T in my 1959 GMC, I noticed a leak in the exhaust manifold gasket. It's a 270 straight 6. (Other than the loud ticking noise, the trip was uneventful. Never overheated despite a constant 60mph.)

I pulled the integrated manifold off and waited 2 weeks to get a replacement gasket. In that time, I noticed a tablespoon of coolant puddled up in one of the now exposed exhaust ports. After wiping it up, it re-appeared after another 2 weeks. I'm thinking its a crack in the head that's leaking into the exhaust port, beyond the valve. No milky oil, no overheating, no vapor in the exhaust that I can see.

If I put my inspection camera through the spark plug hole for that cylinder and find no coolant, would it be reasonable to try some Bars Leaks or other head gasket sealant to repair the leak? GMC 270 parts are kind of hard to come by, not like its Chevy cousin. I'm loath to pull the cylinder head and wind up with this thing inoperable in my driveway for the next 2-3 months. Any "Gotcha's" with this plan?

Oh...and BTW, this is the original motor with 130K on it. (40K under my watch.) In the 2 weeks I waited for the gasket, I painted it and replaced the steel fuel/oil/vacuum lines as I had nothing else to do! Original bottom end, but I had the head rebuilt at 110K miles. Thanks, -Steve
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davedecker4
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Re: Coolant in Exhaust Port **NFC**

Post by davedecker4 » Fri Sep 07, 2018 12:58 am

Hard to believe head would only last 20k miles on a rebuild on that stout stovebolt. I wonder if exhaust manifold leak had anything to do with it? Did you look under that shiny valve cover and see if you notice anything amiss? As its something you like and appear to be inclined to keep for some time, I would pull the head and fix it right.
Dave Decker
a 'couple' Fiats and Lancia's
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San Jose Steve
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Re: Coolant in Exhaust Port **NFC**

Post by San Jose Steve » Fri Sep 07, 2018 2:11 pm

I did pull the valve cover as I initially thought the ticking was the result of a valve with excessive lash. During the valve clearance exercise I noticed the tiny breach of the exhaust manifold gasket. Nothing unusual to be seen there....... Watching it run with the cover off has sort of an "industrial revolution" feel to it. It sounds like a collection of old sewing machines all churning away. I think the design of that motor goes back to the 1930's and powered everything from Army halftracks to Duck boats in WWII.)

I really need to get on the timing belt job on my Fiat. The prospect of having 2 ~50 year old cars in pieces at home at the same time has my stomach burning ! Ugh..... the head on that thing must weigh in excess of 50 pounds! -Steve
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