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1997 Pontiac Grand Prix GT
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Discussion Starter · #1 ·
A few weeks ago now I replaced my LIM gaskets because oil was getting into my coolant (but not the other way around) and it went pretty smooth. Got the GM Aluminum gaskets in there right now and everything seems to have sealed nicely, at least on the outside. I've noticed I've had to top off the coolant twice now and there still seems to be some oily residue in there as well. I'm not sure if it's whatever was left after my less than adequate cooling system flush or if it's still doing it but I'm now more concerned about why it's consuming coolant. It didn't do that before I replaced the gasket and I did everything correctly, torque specs, mating surface cleanup, etc. What's the deal?
 

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If you're referring to the overflow reservoir, it's going to look awful due to prior Dexcool gunk.

For filling, I recommend getting the funnel setup that goes on the radiator cap, and allows purging/burping as the engine initially runs. You can squeeze the upper radiator hose as bubbles escape. This helped me with my setup that has extra coolant lines for the turbo and extended thermostat hose for the Holden intake.
 

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Discussion Starter · #3 ·
If you're referring to the overflow reservoir, it's going to look awful due to prior Dexcool gunk.

For filling, I recommend getting the funnel setup that goes on the radiator cap, and allows purging/burping as the engine initially runs. You can squeeze the upper radiator hose as bubbles escape. This helped me with my setup that has extra coolant lines for the turbo and extended thermostat hose for the Holden intake.
It's already been filled and bled properly, the system has been dexcool free for a long time now. The engine seems to be consuming coolant somewhere after replacing LIM gaskets.
 

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Possibly replace/upgrade your clamps on both ends of the radiator and heater core hoses from spring-type to worm-gear or t-bolt style. This will help ensure nothing is getting in/out at those points for just a few dollars and a little time/spillage to swap them.

You can also do a pressure test to determine where the leak is.

Another problem area can be the upper intake, where the 2 coolant holes go to the throttle body, using o-ring's to seal them. Many of us who modify things typically tap/seal these with 3/8" NPT plugs to eliminate any issue.

Also, ensure your coolant elbows on the alternator bracket aren't slowly leaking. Reinforcing the o-ring seals of the elbows with RTV can assist there.
 

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Discussion Starter · #5 ·
Possibly replace/upgrade your clamps on both ends of the radiator and heater core hoses from spring-type to worm-gear or t-bolt style. This will help ensure nothing is getting in/out at those points for just a few dollars and a little time/spillage to swap them.

You can also do a pressure test to determine where the leak is.

Another problem area can be the upper intake, where the 2 coolant holes go to the throttle body, using o-ring's to seal them. Many of us who modify things typically tap/seal these with 3/8" NPT plugs to eliminate any issue.

Also, ensure your coolant elbows on the alternator bracket aren't slowly leaking. Reinforcing the o-ring seals of the elbows with RTV can assist there.
I'll check the upper manifold and if nothing else get a pressure test done. The coolant elbows are already metal and the hose clamps are all worm gear styled luckily. Would blocking off the passages to the TB cause any issues?
 

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The elbows being metal isn't so much a leak-point removal, but more of a replacement part introduced after the plastic ones would break during removal (some may get brittle and crack/leak near the o-ring over time, too). The o-ring's on either style are what seal those connections, and they aren't always the best fit for the opening, which is why some RTV spread around each o-ring is a good practice.

The TB on many cars get coolant thru them to prevent the rare occurrence of freezing open in extreme cold. That's not a real concern with 3800's, being right above the exhaust and having sufficient return spring. I've helped a bunch of folks in northern states, including myself, block these on cars driven in sub-zero conditions without concern. I'm sure you could try inducing this failure on a cold car in -40* weather that you immediately go 100% throttle on right after starting, but I'd bet it's still going to be fine (your bearings, however, may complain).
 

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Discussion Starter · #7 ·
The elbows being metal isn't so much a leak-point removal, but more of a replacement part introduced after the plastic ones would break during removal (some may get brittle and crack/leak near the o-ring over time, too). The o-ring's on either style are what seal those connections, and they aren't always the best fit for the opening, which is why some RTV spread around each o-ring is a good practice.

The TB on many cars get coolant thru them to prevent the rare occurrence of freezing open in extreme cold. That's not a real concern with 3800's, being right above the exhaust and having sufficient return spring. I've helped a bunch of folks in northern states, including myself, block these on cars driven in sub-zero conditions without concern. I'm sure you could try inducing this failure on a cold car in -40* weather that you immediately go 100% throttle on right after starting, but I'd bet it's still going to be fine (your bearings, however, may complain).
So it looks like it's leaking externally at the driver side of the manifold. I should've used RTV on that little side seal but I didn't and it didn't quite seal at the space between that and the gasket for the ports. Should it be ok if I just pop the manifold off, clean it up a little, and dab some RTV on those edges? Or will I need to buy yet another gasket set. The ones I have are metal GM ones and they're not even a month old.
 

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I've re-used the aluminum ones with minor wear before, and definitely use a dab of RTV to fill the 4 corner gaps when installing those. Kinda odd that coolant is coming from there, though. That's only supposed to seal the valley where oil is settling from the valvetrain, while coolant should stay sealed in the square passages in the center of the LIM gaskets, and the top of the plenum. Make sure you're also putting some PTFE sealant on the LIM bolts (tape or paste, pick your poison), since some go into coolant passages in the heads.

Also check the thermostat seal, and possibly refresh it with a thin layer of RTV instead of a paper gasket, to ensure it's good.
 

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Discussion Starter · #9 ·
I've re-used the aluminum ones with minor wear before, and definitely use a dab of RTV to fill the 4 corner gaps when installing those. Kinda odd that coolant is coming from there, though. That's only supposed to seal the valley where oil is settling from the valvetrain, while coolant should stay sealed in the square passages in the center of the LIM gaskets, and the top of the plenum. Make sure you're also putting some PTFE sealant on the LIM bolts (tape or paste, pick your poison), since some go into coolant passages in the heads.

Also check the thermostat seal, and possibly refresh it with a thin layer of RTV instead of a paper gasket, to ensure it's good.
11208

It's definitely coolant, would it make more sense to come from the upper manifold in that area?
 

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Discussion Starter · #10 ·
I've re-used the aluminum ones with minor wear before, and definitely use a dab of RTV to fill the 4 corner gaps when installing those. Kinda odd that coolant is coming from there, though. That's only supposed to seal the valley where oil is settling from the valvetrain, while coolant should stay sealed in the square passages in the center of the LIM gaskets, and the top of the plenum. Make sure you're also putting some PTFE sealant on the LIM bolts (tape or paste, pick your poison), since some go into coolant passages in the heads.

Also check the thermostat seal, and possibly refresh it with a thin layer of RTV instead of a paper gasket, to ensure it's good.
It actually seems like it's coming from top and bottom...
 

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Any wetness around the water pump and/or the front cover? I might take the belt/pulley off the water pump and give a 1/8-1/4 turn on the bolts and then assess. I had a front cover gasket that needed to be replaced. Was so bad I ran straight water to save $. Of course that won’t work during winter.
 

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Discussion Starter · #12 ·
Any wetness around the water pump and/or the front cover? I might take the belt/pulley off the water pump and give a 1/8-1/4 turn on the bolts and then assess. I had a front cover gasket that needed to be replaced. Was so bad I ran straight water to save $. Of course that won’t work during winter.
Thankfully water pump and front look good still. If I had to replace the water pump then that's pretty much the whole damn accessory routing I'd have replaced then lol. I've already done the alternator, tensioner, power steering pump, and eventually I'll have to do the A/C compressor. The water pumps a trooper haha.
 
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