Intake manifold gasket replacement -adding sealant?

[Oliver S.]

Hi,

my question doesn't specifically pertain to my Corvette but to vintage US V8 cast iron engines in general:
Do you recommend the application of a high temperature sealant beside the intake manifold gasket, too?

Oliver

[Jeff P.]

Re: Intake manifold gasket replacement -adding sealant?

Oliver, I've always used Permatex at the corners of the intake gaskets where they touch the rubber gaskets to make sure they seal that area. Also rubber gaskets are twisted so i add a dab to hold them down on the surface. I've seen some mechanic's simply use silicone sealant instead of the rubber intake gaskets.

[Bruce B.]

Re: Intake manifold gasket replacement -adding sealant?

Many mechanics say throw away the front and rear intake manifold seals and use silicone instead of the rubber seal. NO.

I always use the front and rear rubber seals and I hold them in place with small dabs of black silicone sealer and also put some at each end of the rubber seal where it meets the intake gaskets.

This always results in a good seal with no oil leaks.

[Joe L.]

Re: Intake manifold gasket replacement -adding sealant?

Many mechanics say throw away the front and rear intake manifold seals and use silicone instead of the rubber seal. NO.

I always use the front and rear rubber seals and I hold them in place with small dabs of black silicone sealer and also put some at each end of the rubber seal where it meets the intake gaskets.

This always results in a good seal with no oil leaks.

Bruce-----


GM ceased the use of rubber end seals on all small block and big block engines after 1980. For 1981 and later only formed-in-place silicone RTV was used.

[Domenic T.]

Re: Intake manifold gasket replacement -adding sealant?

Joe,
I have used RTV for years after removing the old rubber ones that got hard and lost their seal and only used RTV on rebuilds. The old rubber seals were so brittle that you had to take them off in pieces.
To stop a leak we used to re-seal the front & back without removing the manifold. We would make a hook and remove the old hard rubber seal, clean the block & manifold with a solvent, then squeeze the RTV where the old seal was and let it cure.

DOM
I can see why some use the rubber because of judging. To bad they don't make them out of something that would stay soft & keep the seal.

DOM

[Joe L.]

Re: Intake manifold gasket replacement -adding sealant?

Joe,
I have used RTV for years after removing the old rubber ones that got hard and lost their seal and only used RTV on rebuilds. The old rubber seals were so brittle that you had to take them off in pieces.
To stop a leak we used to re-seal the front & back without removing the manifold. We would make a hook and remove the old hard rubber seal, clean the block & manifold with a solvent, then squeeze the RTV where the old seal was and let it cure.

DOM
I can see why some use the rubber because of judging. To bad they don't make them out of something that would stay soft & keep the seal.

DOM

Dom-----


Heat is the culprit in the hardening and failure of these rubber end seals. If they made them out of high temp silicone rubber they would probably last. But, they don't. The high temp silicone RTV which GM specified for the end seals post 1980 remains pliable and brittle-free at temperatures far higher than it will ever see in the manifold end seal application.

I use Permatex Ultra Copper or Ultra Black.

One other thing I should have mentioned: the rubber seals are designed for a specific and narrow range of gap between the intake manifold and block bulkheads. However, this gap can vary beyond PRODUCTION tolerances due to SERVICE machining of the cylinder head deck, block deck, or intake manifold. If the resultant gap is too small, the rubber gaskets will over-compress, break, and "squeeze out". If the gap is too large, there will not be sufficient compression on the seal to effect a good seal. With RTV the size of the gap is essentially irrelevant. With RTV, properly applied, you can get a perfect seal every time.

[Terry M.]

Re: Intake manifold gasket replacement -adding sealant?

Dom-----


Heat is the culprit in the hardening and failure of these rubber end seals. If they made them out of high temp silicone rubber they would probably last. But, they don't. The high temp silicone RTV which GM specified for the end seals post 1980 remains pliable and brittle-free at temperatures far higher than it will ever see in the manifold end seal application.

I use Permatex Ultra Copper or Ultra Black.

One other thing I should have mentioned: the rubber seals are designed for a specific and narrow range of gap between the intake manifold and block bulkheads. However, this gap can vary beyond PRODUCTION tolerances due to SERVICE machining of the cylinder head deck, block deck, or intake manifold. If the resultant gap is too small, the rubber gaskets will over-compress, break, and "squeeze out". If the gap is too large, there will not be sufficient compression on the seal to effect a good seal. With RTV the size of the gap is essentially irrelevant. With RTV, properly applied, you can get a perfect seal every time.

The key Joe, is the words properly applied. At the engine plants a machine dispensed a measured quantity at a specific thickness to a properly cleaned location. Then the intake manifold was lowered straight down into place. Good luck doing all that in your garage.

BTW: The RTV rear end seal on GenII LT1s suffers from temperature failure near the passenger side due to the proximity of the EGR tube coming from the passenger side exhaust manifold. To my knowledge there is no permanent cure. Re-sealing the intake is an ongoing maintenance task for these engines.

[Dale O.]

Re: Intake manifold gasket replacement -adding sealant?

Joe or Terry do you know what the gap should be between the block and intake on a chevy small block and big block?

[Terry M.]

Re: Intake manifold gasket replacement -adding sealant?

Joe or Terry do you know what the gap should be between the block and intake on a chevy small block and big block?

Sorry Dale, I do not.

[Joe L.]

Re: Intake manifold gasket replacement -adding sealant?

Joe or Terry do you know what the gap should be between the block and intake on a chevy small block and big block?

Dale-----

I once knew but I've long-since forgotten. I have a habit of not writing things down and relying on my memory. That doesn't always work, though.

[Martin M.]

Re: Intake manifold gasket replacement -adding sealant?

Joe, I suspect your memory is full!!

[Joe L.]

Re: Intake manifold gasket replacement -adding sealant?

Joe, I suspect your memory is full!!

Marty-----


Yes, I need to start deleting stuff so I can get new stuff in.

[Bill H.]

Re: Intake manifold gasket replacement -adding sealant?

I quit using Permatex's Ultras years ago after they came out with "The Right Stuff". It's so much better than RTV.

[Timothy B.]

Re: Intake manifold gasket replacement -adding sealant?

Marty-----


Yes, I need to start deleting stuff so I can get new stuff in.

Joe,

That happens naturally, don't rush it. :-)

[Martin M.]

Re: Intake manifold gasket replacement -adding sealant?

I quit using Permatex's Ultras years ago after they came out with "The Right Stuff". It's so much better than RTV.

I have used "The right stuff" many times. I find it to be an excellent product.