C2 intake manifold bolts leaking

[Wayne K.]

This spring after 6 seasons of use since I had some head work done the 5th intake manifold bolt on the drivers side and the 4th on the passenger side (counting back from the front of the engine) on my L79 started leaking oil. The intake bolts where installed with an application of black RTV and have not shown signs of leaking until now. I recall someone advising the use of clear high temp epoxy to seal leaks. If this would be an option what brand is best and where would I find it.

Thanks,
Wayne

[Harry Sadlock]

Re: C2 intake manifold bolts leaking

Wayne, I had a similar problem after a few years. I resolved the problem by re-torquing the bolts. The shop manual gives a 25 to 35 pound range, start at 30 and increase to 35 to see if the problem is resolved.

Harry

38513

[Terry F.]

Re: C2 intake manifold bolts leaking

They all like to leak there. I am not big on just tightening the bolt down more. In that position, the bolt is probably being splashed by oil from the underside. Once it starts doing that, it is difficult to fix. If you are particular and you could find any other reason to pull the manifold and reseal it, I would do that. But you could try this first....remove the bolt and clean the area with laqure thinner. You will have to clean the threads very well and get them bone dry as best you can. I would leave the bold out a couple of days and keep washing it down with laqure thinner. Then, I would make sure the bolt is in very nice condition or I would replace it with a nice original one (up to you on that). Then I use this white teflon paste that is made by Permatex. I can't remember its actual number or name but it comes in a small can and has a brush with it. It is also the same stuff that is used on head bolts that screw into water jackets. Someone else might read the thread and know what I am talking about. I don't like using silicone type products in that position because it eventually fails and it acts as a lubricant under heat cycles which allows the bolt to come loose. There is nothing worse than dried silicone on oily bolt threads. If you keep adding more silicone and retightening the bolt, little pieces will get down into the engine and can cause problems in oil passages. It does not desolve. Rubbery silicone products work great between two surfaces that are clamped together but not on bolt threads.

If nothing else, call an engine rebuilder and see what product they are using in that position. There are new products coming out all the time and I don't keep up on it. But I tend to stick with what works for me. Remember, you are trying to seal an area that clasicly likes to leak regardless of what you do to prevent it. Good luck, Terry

[Wayne K.]

Re: C2 intake manifold bolts leaking

Terry,

Do the bolts in question or any of the intake manifold bolts for the matter enter areas that I should have a concern about coolant should I remove them as you have suggested.

Wayne

[Terry F.]

Re: C2 intake manifold bolts leaking

I don't recall. I don't think so. I am sure someone on the board knows. I have only rebuilt chevrolet engines but I don't rebuild engines that often. I do recall that some are exposed to oil from the underside. If you use hardening type sealer on the threads and then retorque them, the seal is lost and they will start to leak. Maybe not right away but eventually. Same goes for silicone.

If you see antifreeze coming from around a bolt on the intake, it is probably because the gasket has gone bad. The antifreeze tunnels from the water jacket to the bolt and then comes up around it. Like I said, I don't think that the intake bolts screw into water passages.

A little oil does not bother me because it is typical to see in that area. But a clean dry engine is prefered. Terry

[Ralph E.]

Re: C2 intake manifold bolts leaking

Wayne,
Why don't you just remove one bolt at a time, re-seal with teflon sealant and re-torque. Seems like it should work to me. My $.02

Ralph #37280

[Terry F.]

Re: C2 intake manifold bolts leaking

If there is any sort of silicone in the threads, you have to get it out of there or it will contribute to a second failure. It is hard to get that stuff out of the threads. Terry

[Craig S.]

Re: C2 intake manifold bolts leaking

No coolant behind the intake manifold bolts......some are not blind and have oil on the backside. The threads must be very clean and oil free on both the bolts and the heads to seal. Use a good brake cleaner that has a fast evaporation rate and leaves no residue such as Albany Brake cleaner. A little in the heads won't hurt a thing and will evaporate right off, I use it to clean almost everything. Make sure you are careful though not to drop small chunks of silicone sealant from the last seal job into the heads so it flushes back into the crankcase from the rocker area. I would use a good non-hardening sealer such as permatex or ARP thread sealer...you should be fine.....Craig

[Craig S.]

Re: C2 intake manifold bolts leaking

You are right, it has to come out.....I would use a thread chasing tap and a vacuum so it doesn't drive it into the oil drainback areas...Craig

[Terry F.]

Re: C2 intake manifold bolts leaking

It is tough to get that silicone stuff out. The best way is to bake the block or head. But, not very likely in this case. Using a tap to chase the threads works but it will drop little chunks of crud into the engine. It will also usually cut the threads wider and leave metal fragments inside the engine. Chasing the threads seems to contribute to bolt hole problems also, especially if the bolts have been retorqued over and over in the past. Can't stand a bolt that is loose in the bolt hole. On an intake manifold, they seem to always back out. The one's that seem to have the most problems always seem to be next to the water jackets.

It is not that big a deal to pull the manifold and put it back together. I would probably do that if it was leaking bad.

Funny thing, I have never gotten away with torqing those bolts to what the manual says. I seem to always give them a little more to keep them from leaking.

Allllllll for now, Terry

[Mike M.]

Re: C2 intake manifold bolts leaking

It has probably been said here before, but silicon breaks down in petroleum products, especially gasoline. Try soaking a piece of silicon tubing in gas or oil some time and see what results. Silicon has its place as a sealant in automobile engines but misuse is rampant. And if overapplied, the material not captured in the "compressed" area degrades quickly and ends up as a blob in the oil pan. That is the reason I went back to Permatex a number of years ago for almost anything that will see gas or oil.

[John H.]

Re: C2 intake manifold bolts leaking

I've used ARP Thread Sealer on head and intake bolts for many years, never had a leaker; Permatex also makes a thread sealer. I don't care for RTV/silicone on bolt threads either.