98 7.4 Vortec intake manifold leak

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TPMLE

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Back in 2014 I did my upper & lower intake manifold gaskets as I saw coolant leaking out in basically the same place as the attached photo shows. After the gasket replacement I didn't notice any leaks for a few years, but starting about 2 years ago I started to see coolant leakage in the same location. It seems to get worse in winter to the point I might see a few drops on the ground where the coolant flows back toward the firewall in the valley between the valve cover and intake manifold. I only see coolant leaking when the engine is off. Funny thing is that if I look into the radiator level the coolant almost shows no difference in the coolant level over time. I just drove it 700 miles a few weeks ago towing my 7500 lb trailer and seems like there was no difference in the coolant level before and after. If I look at the engine while it is warmed up there is no evidence of any leakage. I had the oil tested at Blackstone and the results showed Sodium levels of 96 ppm (universal avg is 35) and potassium was 259 (universal avg is 6). All of the other oil parameters were within acceptable ranges, though copper levels were 33 and the universal avg was 9. Blackstone mentioned the higher wear levels of copper might be due to the excess coolant. So it looks like some is leaking into the oil. How bad these levels are I'm not sure, but I understand it should be close to the unversal avg.

My question is if I go back in and do this again, what might I have done incorrectly or might do better this time. I read there are many opinions on how & where one should place a bead of caulk along the wall in the front and back (I just put a bead of caulk at the ends, where the rubber gasket touches the gasket), whether one should put permatex on the intake manifold bolts ( I didn't, I think I put thread locker on them). Interested in getting thoughts on the best methods for sealing and replacing the 7.4 Vortec lower intake manifold.
 

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454cid

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People tend to use some sort of sealer on the intake bolts instead of the loctite that GM specs. The bolts start to back out, and you get a leak. That's what happened to me, when I paid to have the intake manifold done.
 

Piratehunter

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The orange coolant will eat the surface of the intake manifold at the crossover. This possibility what is going on. When you pull the lower and it is pitted in that area, clean it really well with brushing and your preferred cleaning fluid, then fill in those pits with jbweld or similar, and file/ sand smooth. The green coolant isn’t as toxic on the manifold. Sealer on the bolts.
 

fisher

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Back in 2014 I did my upper & lower intake manifold gaskets as I saw coolant leaking out in basically the same place as the attached photo shows. After the gasket replacement I didn't notice any leaks for a few years, but starting about 2 years ago I started to see coolant leakage in the same location. It seems to get worse in winter to the point I might see a few drops on the ground where the coolant flows back toward the firewall in the valley between the valve cover and intake manifold. I only see coolant leaking when the engine is off. Funny thing is that if I look into the radiator level the coolant almost shows no difference in the coolant level over time. I just drove it 700 miles a few weeks ago towing my 7500 lb trailer and seems like there was no difference in the coolant level before and after. If I look at the engine while it is warmed up there is no evidence of any leakage. I had the oil tested at Blackstone and the results showed Sodium levels of 96 ppm (universal avg is 35) and potassium was 259 (universal avg is 6). All of the other oil parameters were within acceptable ranges, though copper levels were 33 and the universal avg was 9. Blackstone mentioned the higher wear levels of copper might be due to the excess coolant. So it looks like some is leaking into the oil. How bad these levels are I'm not sure, but I understand it should be close to the unversal avg.

My question is if I go back in and do this again, what might I have done incorrectly or might do better this time. I read there are many opinions on how & where one should place a bead of caulk along the wall in the front and back (I just put a bead of caulk at the ends, where the rubber gasket touches the gasket), whether one should put permatex on the intake manifold bolts ( I didn't, I think I put thread locker on them). Interested in getting thoughts on the best methods for sealing and replacing the 7.4 Vortec lower intake manifold.
The dreaded intake manifold coolant leak. I've done this repair 4 times in 23 years on my 2000 k2500 with L29 engine with 213,000 miles. It's a common problem. The heads get pitted around the coolant passages on the front corners, and the back corners. I haven't done the jb weld fill technique like piratehunter mentioned. That might be the only semi-longterm solution. The lower gaskets seem to distort over time around those corners and then leak. I've tried different gasket brands with none lasting over 50-60 k. I tried a bead of rtv around the corner coolant passages to see if that would help. It didn't. Wished I had the magic solution. I don't believe thread sealant on the bolts has anything to do with it. The service manual calls for thread lock. I've used blue and red with the same result. Tear it down and put back together like the manual says and don't be in a hurry. Clean out all the bolt holes on the heads thoroughly so the bolts will torque down evenly. That will save your engine until the next coolant leak.
 

TPMLE

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The orange coolant will eat the surface of the intake manifold at the crossover. This possibility what is going on. When you pull the lower and it is pitted in that area, clean it really well with brushing and your preferred cleaning fluid, then fill in those pits with jbweld or similar, and file/ sand smooth. The green coolant isn’t as toxic on the manifold. Sealer on the bolts.
I switched over to the green coolant a long time ago, before I did the gasket replacement the first time.
 

Schurkey

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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.
 

fisher

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I switched over to the green coolant a long time ago, before I did the gasket replacement the first time.
Dexcool seems to be hard on lower intake gaskets. Really softens and distorts the gaskets at the corner passages. How long since your last gasket repair and coolant swap?
 

TPMLE

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I bought this truck, 1998 CCLB C3500, in 2002 used, it had 42K on it, I flushed the dexcool right away. First and only manifold gaskets replaced at 143K in 2014. Now it has 173K miles on it. I’ve driven it much less these past few years as I’ve been working from home since Covid started. It used to be my drive to work car.
 

TPMLE

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Looking at my Blackstone oil report, it says potassium level was 256 ppm. That is a volume percent
256 ppm = 0.000256 of total volume
7 quarts of oil x 0.000256 = 0.001792 quarts
0.001792 quarts = 0.344 teaspoon
I don’t know but it just seems like a really small amount to be overly worried about
 

Piratehunter

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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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