I broke in my newly rebuilt 340 last week with no problems, and did not run it again until tonight. I broke it in with no thermostat installed, but replaced it afterwards.

Tonight I shut the motor down after a few minutes of running, and shortly after shutting it off I noticed a hissing noise and steam coming from rear passenger side exhaust manifold. Coolant appears to be coming from around the second bolt from rear on passenger side, or the bolt just to the right of the rear outer stud.

Is this bolt exposed to the water jacket?

All four outer studs were sealed with Rector-seal so I don't think it's coming from there, but I don't believe any of the other bolts were. I am hoping that all I have to do is drain the fluid down and reseal all bolts. Do all small-block exhaust bolts contact the water jacket? Also, it seems that water only leaks after engine is shut off and pressure builds...

Any thoughts on this?

Thanks!

Brian

yes only the 4 corner bolts are wet. I'd pull that sides' ex manifold & likely you will see where the problem is without having pump it up. EDIT If you can pull that corner stud out WO removing the manifold you could reseal it with some thick cement (permatex #1 or #2 in the toothpaste like tube or some of "the right stuff"). Drain the coolant down & spray the hole well with Brake Kleen (make sure you're in the open we dont wanna get cancer) & let it dry well (blow it out with shop air) then goop up the threads

Pull the end stud and reseal it. Make sure the stud is good and tight. Is it a factory stud in there or a replacement stud? If it leaks again, check for cracks around the hole. The other bolt you are referring to doesn`t enter into coolant.

I had the same thing happen with my 440. I drained the coolant, removed the stud, and cleaned with brake clean. I used permatex (i forget which one) and re-installed the stud. I waited 24 hours before I re-filled the coolant and started the engine. It's been 4 years now without any leaks. Good luck.

good luck pulling those studs! use caution. I cant get mine out. gotta live with exhaust leak until I pull heads

Chances are it's the corner std as many have already indicated, the problem could be compounded if/when the heads were done by a machine shop (I assume the heads were done?)a helicoil was inserted possibly to replace/repair the threads?, if so sealing the stud (assuming it was removed/replaced) won't seal the outer threads of the helicoil coolant will still creep by, I had this happen on my smblk stroker, if this is the case, you'll need to drain the block, pull the stud, douche the hole with carb cleaner,compressed air to dry it, inject some hi temp silicone (gold permatex) into the hole, lube up the threads with the same, no tape, install let it sit for a for about 2 days to cure

Mike

Oh that's right, forgot about that, it may take the hot wrench to get it out (likely cuz those corner ones have been in there since day 1) but I would pull the manifold & go from there with what you see

He said they were resealed already so I don`t think removing them will be a problem. I helicoiled two of my stud holes on my 340 and never had a issue. The factory studs seem to have a better taper on them where they meet the head then aftermarket studs, that why I was asking if he used OE or not.

Yes, I only installed them in the last month or two, so everything should still come apart pretty easy.

I am going to pull manifold today, and I'll report back!

Thanks!

Yes, missed that. I'd get another stud (As said OE of you can find one even a good used one)/prep the hole & I'd use some of "the right stuff". I've used that stuff on gaskets that would not seal any other way (stat housings) tho it is a gasket maker in & of itself

I removed the manifold (and destroyed the new gasket in the process-my luck) and there doesn't appear to be any cracks in the head. On way to go pick up new gasket at O'Reilly's so I'll pick up some Great Stuff or whatever I can find there. I only have pipe thread sealant and hi-temp RTV at the house. I used pipe thread sealant on the other corners but they seem to be holding up well! I wonder if I should reseal those or leave well enough alone?

its "the right stuff" (thats the name of it) Permatex gasket maker & not needed for the exhaust manifold gasket (& it sure ain't cheap). your other corners are fine, Take care of this one & you're set. Do you have the stud out?

Yes-stud is out and looks perfectly fine!

So could I go with the pipe sealant (500 deg range) or Red Hi Temp RTV that I have on hand or do I need to go with something more, like Copper Ultra temp RTV or Right Stuff?

Right Stuff was like $20 for a tube and I only need a pinch. I'll get it if I have to though.

Man that is a tough call (I hate to waste other peoples' money, mine I'm ok with squandering!). I think I would go with a generous amt of pipe dope but I dont remember if you used it earlier & if so & it leaked then I think I would go with TRS. Coolant leaks are the cats' ass to deal with. bristle brush and brake Kleen for prep (you dont need a comeback)

Pipe dope will not work, they are not pipe threads.

correct, the studs are not pipe threads. but loctite 576 pipe sealant works great for sealing ALL threads. i have used this stuff for years sealing head studs and intake manifold bolts that weep oil. it flat out works for pipe threads used with water, gasoline, alcohol, natural gas, oil, and just about anything you can think of. it's perfect for stainless and aluminum fittings that tend to gall when assembled. it is a teflon paste. i seldom use anything else.

I ain't used it myself but I've heard good reports on it

I did use pipe dope om the other threads and didn't have a problem. When I removed the manifold to check for possible cracks, I damaged the gasket so I ran to auto store for a replacement. I also noticed the front manifold stud was loose, but not leaking. Since it was right in front of me I removed it and cleaned the hole out with brake cleaner, and I rolled the dice on Hi-Temp RTV since I already had it. I will keep an eye on it, and worst-case scenario I'll have to remove manifold and reseal with something better...

Thanks for all of the help and I'll keep y'all posted!

Fired it back up, and leak has stopped. Now I noticed smaller leak on driver's side. Well, at least I know how to fix it now...

Brian your luck will change soon