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Working on my '96 SSE L36 with 232,000 miles. At 180,000 I replace LIM gaskets with GM aluminum and installed APN UIM. 50,000 miles later I have a coolant leak at the throttle body gasket. I removed and cleaned the TB, installed a new orange felpro TB gasket and replaced. The mating surface on the APN manifold is visibly warped where it meets the TB. TB surface checks flat with straight edge. The orange gasket can be seen through the gap looking at the front of the manifold between the upper and lower TB mounting bolts. (I will try to post a picture later)

I removed the top plastic engine cover (heat blanket!) and the engine has never been overheated.

What is the normal life expectancy of these APN uppers? I had hoped this was a "permenant" fix that would get me to 300,000 or more. What should I do at this point? It's obvious that the UIM has to be changed AGAIN. Should I go back with another APN or Dorman or GM or something else?

Man I'm tired of these plastic intakes. I thought I had this thing fixed for good.

Just looked at APN website. Their UIM has a 12 month 12,000 mile warranty. Whoooptydoooooo that helps a lot.

Tumbleweed... Did it stop the leak?

Its normal to see that gasket, they all do it just the same.. I bet I know exactly what I will see when you post the pic, get it posted so I can be sure... But I don't think you'll have any more issues..

I agree. If the leak has stopped, I don't think I'd worry about it. I put a Dorman UIM on my son's Grand Prix, along with a sleeve from Bill Buttermore, before the APN was available. Even brand new, there was a gap between the throttle body and upper intake, where the gasket could be seen. That was several years ago, and it's still fine.

I can see TB gasket on my OEM UIM. It's holding. Not sure how the APN will fare.

Sorry it took so long to get back with a pic. We have been trying to keep the combines going on corn harvest and we have another rain delay today.

I'm away from the shop and I don't have any high tech measuring equipment at the house so I used my redneck method. A dime and quarter stacked together will fit in the gap between the UIM and the TB in the area where the gasket is visible. I guess you could say I have $0.35 of clearance.

The anti-freeze is pooling on the LIM just to the left of the thermostat housing. The thermostat has not been removed or otherwise tampered with recently so I do not suspect a leaking therm gasket but anything is possible.

I'm open for suggestions.....

I need to spray a little whiff of ether around the gasket and check for air leaks.

Well, we hoped the APN would be the last fix. As far as we know, it is still the best commercially-available fix. Like the others have said, this gap at the throttle body appears on UIMs by all makers so far. I suppose it might be possible to make the warp a little worse by over-torquing the nuts that fix the throttle body to the UIM. That soft silicone gasket doesn't take much to seal - 7.5 ft-lb. I know there is a very different torque spec (and a different style gasket) for the TB bolts on the metal upper intake (supercharger) on the L67s - 20 ft-lb. Anyway, I think it might be worth your time to call APN (ineedparts.com), explain the problem and ask if they would replace the UIM for you. They can only say no.

Thanks Bill,

I do plan to visit with a tech rep at APN and get their thoughts. I do appreciate hearing from other users about their experiences with the APN part and how many miles they are getting out of them.

I don't want anyone to think I am "bad mouthing" APN as I think it is still probably the best fix available. I know "stuff" happens and sometimes problems pop up.

Tumbleweed if you had used the black GM throttle body gasket instead of the supplied orange gasket the plastic would have warped less.
The orange gaskets are so dense the plastic intake will warp before the rubber gasket compresses.

My original GM and Dorman replacement upper plastic intake looked just like your picture with the orange gasket showing.

Throttle body gap using black GM rubber gasket.

Thanks for the tip, Ron. I have added this information to the Techinfo article for changing the UIM. How long since the black gasket was installed when the photo was taken?

Bill I got all my L36 information from this forum years ago.
Looking at your article and Jrs3800 article I see both show the APN plastic intake fitted with the upgraded (more flexible) Black throttle body gasket?
Did the APN come with the black gasket or did the installer put it in?





“I want to thank Mkaake, Bill Buttermore, Bob Dillon, Boosty, Bill Wren, Arbelac, Showshocka2k, and everyone that had made this upper intake knowledge possible. Thanks everyone. This continues to be a work in progress so if there are any part numbers you want added or any more info please PM me, Jr's3800... Thanks again”

http://www.pontiacbonnevilleclub.com/fo ... =53&t=3591

http://www.pontiacbonnevilleclub.com/fo ... =53&t=1061

My motor has less than 1K miles on it since I took that picture so it is not a good example to judge TB flange warping.

I used the black gasket when the APN was installed new. It had the black gasket in place for 50,000 and I replaced it with the orange felpro about 2 weeks ago when I cleaned the TB. That is when I noticed the warped surface on the APN.

After reading your post, I will replace the orange felpro with a black GM gasket and see how it works.

Thanks!

The APN installed onto my car had a black gasket, and a straight TB opening. I hope this doesn't happen to mine!