Coolant Leak 72 350 engine

[brown7373]

I am installing a 350/290 crate engine. Pretty much everything is together and I was filling it with coolant, when I saw coolant laying on the right side intake to head. Everything is stock. I used the stock 4 BBL intake with the Fel-Pro gaskets and used silicone at the front and rear of the intake and around the water passages.

It looks like the leak is at the front 2 intake bolts or the intake water passage. The bolts don't appear to go into the water passage, but it appears to be leaking around the water passage or from those bolts. Any ideas on what I should do?

The engine has NOT been fired. This happened while filling the engine and radiator.

[rcazwillis]

If it is leaking with out any pressure, you have a gasket issue. I would take the intake back off and reset the gaskets.

Is it coming from a heater hose or the top radiator hose? Picture of area would help.

[HO455]

I can't speak for every block but on my 350 (1974) all of the intake bolts go through to the water passages. If you have a radiator pressure tester it would make short work of finding your leak before tearing the intake off. You may be able to rent/ borrow one from a parts store.

https://www.2carpros.com/articles/ra...-pressure-test

[brown7373]

I see no indication it is coming from the heater hose or the thermostat housing. It pools by the front intake bolt then runs toward the back.

[geezer#99]

Drain the rad so there’s no coolant that can push out and pull that bolt and put some sealant on it.
That might stop it.
Is that the correct bolt?

[geezer#99]

Here’s an example of the style of bolt that likely should be used there.
https://www.kimballmidwest.com/All-P...and-Nuts/27756

[cleszkie]

All intake manifold bolts should have the threads treated with Teflon thread sealant. If you are getting a leak with no pressure then you have a big leak. Not to set off any alarms, but if you don't find the source of your leak I'd check the intake and head for cracks in the water passages next to the bolts.

[brown7373]

Why would a stud go there? That isn't where the battery ground attaches. That is a replacement bolt. Maybe too long? Hmmmm

[brown7373]

I just checked and I was wrong. Those are the original bolts. The flash made them look gold cad, but they are not. But maybe the threads were not sealed properly. The battery cable attaches under the A/C compressor to the front of the head.

[geezer#99]

A step stud would work to stop a leak better than the bracket.
And tighten the intake down.
I see you have a stud with a nut on it on the other side of the choke pad.
Perhaps you need two more just like it to attach the bracket for the a/c.

[brown7373]

Several intake bolts had to be removed to install a bracket after the intake was torqued. Studs would have helped. I think I will order several studs and nuts. My 455 Pontiac has several stud/nut bolts to attach various accessories and brackets, but there were none on this PU engine. The first bolt on the intake attaches an A/C bracket and would definitely be better with the stud. The next 2 attach rear A/C bracket and would also benefit with stud/nut bolts, as well as the bolts that hold the spark plug wire looms. Anyone know the bolt size off hand?

I bought a radiator pressure tester from Harbor Freight but it won't work. The adapter for GM is too small. Must be for late model. I will try to rent one.

[garyd1961]

Put some thread tape or thread sealant on the bolts. No need to buy new stud bolts it would throw your alignment off anyways.

[brown7373]

I checked my original intake bolts today, and I have 2 stud/nuts. One stud attaches the support for the oil fill tube and the other is installed doing nothing. I am thinking that should probably go in the right side number one, that holds the front A/C bracket to the manifold. Does anyone have an original with A/C who can confirm that?

[geezer#99]

Oil fill tube?
What year is your intake manifold?

[brown7373]

This is a 1972 with factory A/C. Maybe non A/C trucks didn't use the tube.

[68 P.O.S.]

Originally Posted by cleszkie

All intake manifold bolts should have the threads treated with Teflon thread sealant. If you are getting a leak with no pressure then you have a big leak. Not to set off any alarms, but if you don't find the source of your leak I'd check the intake and head for cracks in the water passages next to the bolts.

Bingo!

[57rookie]

Pull the bolt and put some thread sealant on the bolt - white in color. And then retorque down. Should fix it. I had a similar problem.

[cleszkie]

Another thought - In the close up shot of your engine and pooling locations it appears that the intake manifold gasket has a pattern on it that looks like the sealing compound on Felpro Perma-Torque intake manifold gaskets. It is not lined up with, and underneath, the intake manifold runners though. Could you have the wrong intake manifold gasket on there? What are those lines making the pattern? If they are raised a bit, they may be intended to align with a different application. Long shot I know, but now I am curious.

[68 P.O.S.]

Originally Posted by cleszkie

Another thought - In the close up shot of your engine and pooling locations it appears that the intake manifold gasket has a pattern on it that looks like the sealing compound on Felpro Perma-Torque intake manifold gaskets. It is not lined up with, and underneath, the intake manifold runners though. Could you have the wrong intake manifold gasket on there? What are those lines making the pattern? If they are raised a bit, they may be intended to align with a different application. Long shot I know, but now I am curious.

Good eye!

I also noticed in the 1st and 3rd pics there's an open vacuum tee in front of the carb. You might want to cap that vacuum leak off

[brown7373]

The engine has not been started yet and I am replacing vacuum hoses, and some are just laying there and not yet cut to length or connected.

[brown7373]

As far as the gasket, I'm not sure. I know all the ports and heater connector lined up. I don't think it can go on upside down and still line up. Switching side to side? But I think the 2 are identical and not marked left or right.