98 7.4 Vortec intake manifold leak

Schurkey said:

IS THE MANIFOLD BASE GASKET SURFACE FLAT? Multiple leakages makes me suspect that the manifold is warped, even if it isn't pitted. It may be both warped AND pitted. Plane the manifold, which will remove some or all of the pitting. If there's pitting remaining after it's been shaved, fill the pits in with epoxy as stated earlier.

Depending on how much material is removed from the manifold, you may/may not have to use thicker manifold gaskets to take up the extra room. (Probably not.)

The rubber end-seals on the "China Walls" can be entirely replaced with QUALITY RTV Silicone. When it's me, the O-N-L-Y stuff I'll use there is Permatex The Right Stuff. When the rubber seals are replaced by RTV Silicone, there's no stress on the manifold pushing "up" as the manifold bolts are tightened.

Fel-Pro claims that their gaskets need no gasket sealer...but I still want to stick the gaskets to the cylinder head with Gasgacinch or some other gasket sealer. RTV Silicone is not a gasket sealer. It's used INSTEAD of a gasket (or rubber seal), not applied TO a gasket.

Click to expand...

Does the Gasgacinch need to go on both sides of the lower gasket coolant ports?

Schurkey said:

IS THE MANIFOLD BASE GASKET SURFACE FLAT? Multiple leakages makes me suspect that the manifold is warped, even if it isn't pitted. It may be both warped AND pitted. Plane the manifold, which will remove some or all of the pitting. If there's pitting remaining after it's been shaved, fill the pits in with epoxy as stated earlier.

Depending on how much material is removed from the manifold, you may/may not have to use thicker manifold gaskets to take up the extra room. (Probably not.)

The rubber end-seals on the "China Walls" can be entirely replaced with QUALITY RTV Silicone. When it's me, the O-N-L-Y stuff I'll use there is Permatex The Right Stuff. When the rubber seals are replaced by RTV Silicone, there's no stress on the manifold pushing "up" as the manifold bolts are tightened.

Fel-Pro claims that their gaskets need no gasket sealer...but I still want to stick the gaskets to the cylinder head with Gasgacinch or some other gasket sealer. RTV Silicone is not a gasket sealer. It's used INSTEAD of a gasket (or rubber seal), not applied TO a gasket.

Click to expand...

I've used a very thin bead of RTV around the pitted coolant passages successful at 180k 5.7L (sold the truck after 50k and 5 years after the install)

But also switched to green coolant.

TPMLE said:

Does the Gasgacinch need to go on both sides of the lower gasket coolant ports?

Click to expand...

I suppose you could. I don't think it's required. I hate scraping gaskets off both surfaces, when they split down the middle and stick to both parts.

eXo0us said:

I've used a very thin bead of RTV around the pitted coolant passages successful at 180k 5.7L (sold the truck after 50k and 5 years after the install)

But also switched to green coolant.

Click to expand...

Cycling back through this now that I am in the middle of replacing the intake manifold gasket. Did you place the thin bead of RTV around the coolant passages directly on the aluminum manifold, or the cast iron head, or both?

After I replaced the Gaskets on my Vortec 5.7L with dry Fel-Pro - I had another leak just a couple of weeks later.

So I got a new set of FEL-PRO MIK 98000 T Intake Manifold Gasket Set.
and a tube of Permatex 82180 Ultra Black

I've cleaned the heck out of the intake and the head. The intake aluminum was good and minimal pitting but the head was pretty messed up.

Procedure:

Put 2 studs in the screw holes of the heads to help as guide setting down the intake straight. - do a few dry runs of setting it down without gaskets. (works for Vortec heads)

Then I applied the black RTV to the gasket rear - where it meets the iron head - just enough to fill the grooves on the gasket surface. Put the gasket on both heads with the RTV still wet.

Apply a thick bead of RTV to the China Walls

apply a very very thin - barely a coating to the gasket around coolant passage of the intake side.

now need to be fast - since that stuff skins over fast with that little thickness.

Put down the intake - and torque the 8 screws to the first stage. (there are 3) set a timer and wait for 30-60 minutes depending on outside temperature.

Come back and torque the intake with the final two rounds.

Wait -at least 24 hours. Fill up coolant and hope for the best

Here are some photos of the intake manifold job I did on my 98 C3500 recently along with replacing the fuel injectors.

Piratehunter said:

well it is leaking now, only going to get worse. invest some to fix it now, or invest more later when the gasket totally gives out. +1 on the Right Stuff on the china walls, without rubber gasket.

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I know this is old, but are saying go ditch the rubber gaskets for China walls and use the right stuff? Or to use the right stuff if you don’t have the rubber gasket

ditch the rubber gaskets for the china wall and use the Right Stuff.

Also if there coolant showing up above the front passenger side intake bolts, it can be the heater hose seal. Oring in there can leak at higher rpm while sealing at idle.