Coolant leak

JohnnyBgood

JohnnyBgood

Well-Known Member
Supporting Member
1977 350 Chevy motor. Installed intake manifold and it leaked coolant between the intake and head above the second intake bolt on both sides. It's not coming from the bolt..it's above the bolt .Took off manifold and redid everything again. Used gaskets on the side and high heat silicon as the front and back gaskets. Put a little bit of silicon around each water port ..Still leaking in the same spots...any ideas? Have done several motors the same way and never a issue..something is wrong and I just can't put my finger on it...
 
The only thing I can think of is a casting defect in the intake ,or a crack,assuming it is cast ,not aluminum. It can be fixed with JB weld if it is .
 
Intake is aluminum...no cracks ...was looking at it today and it looks like both ends seemed to be concaved. It's slight but it's there...right where it leaks. This was a used intake when I got it and I think someone sanded down some corrosion around the water passages. Wish I would have seen it before I payed to powder coat it and spent the time installing it. I was convinced that somehow it was the wife's fault but I guess not...now I gotta find another intake with egr but no choke pocket.
 
I wouldn't rule out the JB . It bonds to aluminum too. Spread a coat over the concaved area and sand it down when dry. You have nothing to lose.
 
It sounds like these two bolt holes penetrate the water jacket in the head and the coolant is coming up the threads. Did you seal the bolt threads? If not try sealing them with Permatex. It looks like most intake gaskets have sealing beads around the ports but not around the bolt holes, so if the coolant comes up the bolt threads it will come out between the head and the manifold.

Also, before installing the intake, I would set it in place without the gaskets and check that it won't rock and go around with a feeler gauge to see if there are any gaps between the mating surfaces that might need to be corrected. If the intake rocks, then a more serious issue like, the intake is warped or a head alignment dowel is missing, or ???

But if it's just leaking bolt threads, you can seal them without removing the intake.
 
The water is pooling above the bolt... Where the intake and the head meet there is the edge of the intake..that's where the coolant is sitting..not where the bolt comes through below it. I also found coolant laying in the lifter valley..not a lot but it was there so it is also leaking into the motor. I like the idea of the JB weld but the only issue with that is I have aftermarket brackets for the compressed and alternator. All the brakets use the bolts on the water pump and intake to secure them. It's quite a job to take them off and put them on again if it still leaks...if never used that JB weld...is it permanent and not affected by the oil and coolant?...I'm hoping to drive the car from Ontario to BC when I move out there so will this weld stuff take the prolonged heat? I might be better to start looking for another manifold....
 
So I was just talking to a neighbour about this. He said he has no idea what the problem is but asked if my measuring tools are good...I said of course..he said let's check...his dad was a machinist when he was alive and had some tools he used to check things. He went and brought over a piece of carbid steel...26 in long and about 1 in wide. Very nice with crisp clean edges..We put it on my manifold and it was touching everywhere. Turns out my straight edge was not straight...so into the scrap bin it went. I looked at the gaskets I took off and you could see where the coolant was getting by on top of the gasket. So like rat rig said..I got nothing to lose...except some time...I'm going wipe everything clean again and give her a try...hmmmm...I wonder if his carbid edge was straight....damn...last issue is the restrictor plate in the centre passage...didn't notice which side it was on...or does it matter??...will have to google that one.
 
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