Slight leak after replacing header gasket....

[Islandvic]

This is concerning my 1995 GMC K1500 350 TBI. When I bought the truck in Aug of '05, a set of FlowTech headers had already been installed. I do not drive the truck much and the past year, the exhaust manifold gaskets started to leak.

The leaks had become very bad, so today I replaced the passenger side gasket with a "Mr. Gasket" piece from Oreily Auto Parts. I dont know the style, but they are not the white paper looking ones, it's very dark grey thick material.

I used a wire brush and removed all the old gasket material before I installed the new one. After I bolted everything up, I fired it up and there seemed to be a slight leak still. It was very late and dark so I'll check it out more Sunday.

I had everything bolted up tight, so what could be some problems? I want to address the passenger side manifold before I start the driver side b/c the alt/ps pump bracket has to be remvoved.

Your comments welcome.

Thanks

 

[Merkava_4]

I'm assuming it's a one piece header flange that goes across all of the exhaust ports right?

I had always thought that header/manifold gaskets are a bright silver material?

Anyway, you might try re-torquing the header flange in a different torque pattern.

You're sure that the head surface and header flange are flat right?

I'm thinking if both surfaces are perfectly flat, and you've used the correct torque sequence, then the gasket itself is at fault.

 

[wileyE]

I've had to split or drill the flange to weaken it. When they weld the tubes to it sometimes warps or is put under stress. or even if it's flat the heat from the exhaust will "pull" on it.

 

[another Todd]

I always use a little high temp silicone on header and ex. manifold gaskets. It fills and seals the gaps caused by slight warpage.

 

[JTK]

Quote:

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I always use a little high temp silicone on header and ex. manifold gaskets. It fills and seals the gaps caused by slight warpage.

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That's a great idea.

Only issue I could see is, could silicone migrate through and sour the oxygen sensor(s)?

Joel

 

[NYEngineer]

I would recheck the header to head surface for flatness and I've never had good luck with the grey gaskets. I've always used the white ones. keep the bolts nice and tight and they won't leak. My buddy's Camaro has a ZZ4 with aluminum heads and Edelbrock headers. He went through header gaskets like candy for some reason, so we finally switched to Percy's copper header gaskets. I think they've been on the car for six years.

 

[another Todd]

Most silicones, I use Ultra Copper, are O2 sensor safe. It should say on the tube if it is.

 

[TwoBills]

I'm going back 40 years, but we always cut the header gasket between the exhaust ports. Seemed to help if I remember right.

 

[occupant]

I forgot to cut the gaskets for my exhaust manifolds on the Intrepid's 3.3 engine. 250 miles and no issues yet.