98 7.4 Vortec intake manifold leak

[TPMLE]

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.

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

 

[eXo0us]

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.

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.

 

[Schurkey]

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

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.

 

[TPMLE]

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.

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?

 

[eXo0us]

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

 

[TPMLE]

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