coolant leak from back of block - Pontiac GTO Forum
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post #1 of 14 (permalink) Old 01-04-2018, 04:43 PM Thread Starter
 
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coolant leak from back of block

1970 pontiac 350 hooked to a th350. After replacing the head gaskets cars been doing great still working out the kinks. Took it for a run the other day about 5 mile round trip, the last light before my turn I was stuck at the light for about 5 min it started to struggle idling then died from the struggle to death it was about 10 sec. It fired right back up then died this is about 3 times finally was able to get it in gear and throttle it and got home with no more issues. Temp stayed around 180 where the t stat is set at idle it holds oil pressure at 25ish under load it goes as high as 60. When parked hot it drips coolant from the back down the k member about a cup or more then stops. I am tempted to point my finger at a warped intake manifold (it was welded after being cracked trying to take out a plug bolt that was locktited on) or a freeze plug in the back. I cant find and puddles or obvious place the coolant is leaking from, anything I can do short of pulling the intake to diagnose?

Thought about the stalling, it might need gas it was showing a quarter tank but my gauge might be wrong? it was the first time other then when the head gasket failed that it stalled out in traffic...I'm more concerned about the coolant leak for now, baby steps...thanks for any input you can offer no idea what I'm doing

Last edited by 1970lemonhead; 01-04-2018 at 04:44 PM. Reason: engine info
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post #2 of 14 (permalink) Old 01-04-2018, 05:41 PM
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I had a small leak at the back I couldn't find, it turned out to be the water port at the front of the engine where the intake mated to the head.
It was leaking underneath and traveling down the gasket between the valley pan and the head.

Last edited by Goat Roper; 01-05-2018 at 12:01 AM. Reason: Spelling error
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post #3 of 14 (permalink) Old 01-04-2018, 07:17 PM Thread Starter
 
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Thanks maybe it warped I'll definitely check the front, what was the fix? Intake probably has to come off anyway I'm thinking now.
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post #4 of 14 (permalink) Old 01-05-2018, 12:18 AM
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I used a thin coat of Ultra Blue gasket sealer on both sides of the intake gaskets just on the two water ports.
Make sure to re torque the intake after running it for a hundred or so miles.
You may want to try re torquing the manifold and see if that fixes it before pulling it.
Keep us updated on what you find.
Oil pressure is fine as is temp.
Check fuel filter(s) and look down the into the carb and work the throttle to make sure your accelerator pump is working properly.
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post #5 of 14 (permalink) Old 01-05-2018, 11:31 AM
 
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Ditto about checking intake torque. My cast iron 69 loosened up to ~25 from 40 ft lbs, and the alum 67 GP started pulling in coolant (much more steam coming from one exhaust pipe). A couple retorques after driving and both were solid. If not done already, use proper torque sequence. I've seen two
https://www.gtoforum.com/f50/torque-s...oil-pan-55778/

you don't have aluminum, but the difference ('spiral') is interesting.
http://www.jegs.com/InstallationInst...0/350-2156.pdf

Hopefully not rear freeze plugs in head. I've seen some where only paint and rust was keeping water in - you should be able to feel liquid if they're leaking.

Would be nice if dying at idle is related to loose intake manifold.
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post #6 of 14 (permalink) Old 01-05-2018, 12:38 PM
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Yup, my manifold also went from 40 to 25 and re torquing also solved my idle problem.
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post #7 of 14 (permalink) Old 01-08-2018, 01:33 PM Thread Starter
 
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Thanks for all the tips, started it today let it warm up after rechecking the manifold bolts still leaks after I turn it off. The valley pan is bone dry. I think it's time it goes to a shop. While I'm here though any recommendations for a decent replacement pair of valve covers? And is fuel line used for the link between the radiator and the Trans line? That's what my Lemans has on it now and it's old and brittle time to replace. This car is an adventure
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post #8 of 14 (permalink) Old 01-08-2018, 04:58 PM
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The valley pan stays dry, it runs in the groove between the valley pan and the head on top of the gasket and pools on the back of the engine.
No fuel line used on the tranny lines, that is a jury rig.

Summit carries your lines and possibly your covers, if not try Ames performance.

https://www.summitracing.com/int/par...c/model/lemans
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post #9 of 14 (permalink) Old 01-08-2018, 07:27 PM
 
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Looks like bad reviews for Summit on those lines.
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post #10 of 14 (permalink) Old 01-08-2018, 08:48 PM
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I actually checked inline tube first but couldn't find them listed.
Summit will replace or refund no problem.
In any event using hose as a mickey mouse repair can cost you a transmission and that needs to be fixed.
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