Continuing Coolant Leak 72 350 engine

[brown7373]

I previously posted, and am continuing to have a coolant leak from my intake. Crate 350/290 engine replacing the original 350 4bbl. I am using my original cast iron intake that had no leaking issues before.

The engine has NOT been started yet. I get coolant leak from the 2nd bolt on the right side, that goes through a U shaped A/C bracket. The leak occurs after I fill the radiator with no pressure on the system.

I tried to remove the bolts and reseal the threads and r-torque, but that changed nothing and failed. I am going to pull the intake and start over, by chasing and cleaning all the bolt threads and sealing surfaces.

I had used Rectorseal TRU-BLU on the threads and Permatex Ultra Black on the front & rear edges and around the coolant ports.

I plan to use ARP Thread Sealer on the threads and Permatex The Right Stuff One Minute Gasket on the front and rear edges. Any suggestions for sealing around the coolant passages?

Does all this sound good, or does anyone have a better suggestion.

[jamyers]

Originally Posted by brown7373

...
I am going to pull the intake and start over, by chasing and cleaning all the bolt threads and sealing surfaces.

...

I plan to use ARP Thread Sealer on the threads and Permatex The Right Stuff One Minute Gasket on the front and rear edges. Any suggestions for sealing around the coolant passages?

Does all this sound good, or does anyone have a better suggestion.

Sounds good to me, although I suggest getting ahold of a good steel straight-edge and confirming that the intake surfaces are flat.

Be sure to use the correct torquing sequence.

Also, I'd use a thin coat of the Right Stuff around all the coolant passages, not just the front and rear ledges. Be sure and torque it down before it sets up (I'm not sure how fast the "one minute" stuff sets)

Also regarding that bracket, hold off on attaching anything to it until you're sure it's not leaking - just so the weight of a compressor isn't part of the equation.

[sick472]

Sounds like a solid plan to me even though I hate to see you have to take the intake back off. I would make sure you have the correct length intake bolt before getting into the big picture. To little thread engagement and the sealer may not be able to do its job, too much and you bottom out on the end or shank before gaining proper grip from the applied torque.

I have only built a few engines, but I have always used Black RTV high-temp in the bolt holes that go through to the water jacket...never had any leak.

Of course, your leak may be from the intake gasket itself and Jamyers has you covered!

[garyd1961]

It has to be either the intake bolt bottoming out and not sealing the gasket, a bad or incorrect gasket, or something is cracked.

[geezer#99]

The bracket isn’t shaped right to fit flat on the manifold. All the bolt tightening in the world won’t keep it from leaking.
You need a stud there. With a nut that tightens down flush on the manifold. That’ll seal it. Then put your bracket on the top part of the stud above the nut. Secure it with another nut.

[68 P.O.S.]

Originally Posted by geezer#99

The bracket isn’t shaped right to fit flat on the manifold. All the bolt tightening in the world won’t keep it from leaking.
You need a stud there. With a nut that tightens down flush on the manifold. That’ll seal it. Then put your bracket on the top part of the stud above the nut. Secure it with another nut.

x2

[Sheepdip]

I am using my original cast iron intake that had no leaking issues before

Had by chance the old tired 350 had it's heads decked and the intake milled to match?

[68 P.O.S.]

This is similar to what you need
https://www.opgi.com/chevelle/CH28770/

[brown7373]

I do not think the engine had ever been touched, but with a 47 year old truck (37 when I bought it), who knows for sure? If I continue to get a leak, I would have to consider that maybe the intake has been cut. But if the original heads had been cut, does the angle change or does the intake just sit a little lower?

[jamyers]

No telling of the intake has been cut, but I'd think it unlikely.

Milling heads won't affect mating surface angle unless they did something fancy like angle-milled them (again, unlikely). Intake will just sit higher relative to the heads.

Even new intakes can be warped, 47-year-olds can easily be not flat anymore. Best to check and confirm *everything* you can - like bolt thread depth as mentioned above.

Also, +2 on swapping out that bracket bolt for a stud - then you'll know you've not bottoming out and have max thread engagement.