Write-Up: Lower Intake Manifold (LIM) Gaskets

This is from the clubgp write up:



The red arrow is pointing towards the fuel rail bolt and the yellow is pointing towards the EGR shield bolt. From your picture, it looks like the hole could be for the EGR shield.

is there another hole towards the front of the car more? is that on the LIM? from the pic it looks like it could be one of the eyelets for the locating pins on the rubber end seals but i cant tell, if its not that i would guess its the EGR shield like you said. can you tell if the hole is threaded or not i cant see in the pic

Actually, my Dads' 99 PA has a series II supercharged 3.8L, and his block also has that hole, with nothing in it. The EGR heat shield bolts onto a black bracket right above that. Anyway, got the job done. It took awhile, the better part of two days, but I had a lot of gunk and dirt on everything, so I took my time and cleaned everything before it went back on, I was quite maticulous with the cleaning process. I also changed the oil and filter and filled the rad up. I started her up, and while I was topping up the coolant, the RPMs went CRAZY, going way high then dropping and then taking off again, idling at 1500. So I took it for a drive and it seems to have ironed out most wrinkles, just hope it doesn't return.

How is it running after having taken it for a ride.?

It seems to be OK right now, I'm just wondering in the cooler morning, what it will do. In the GTP write it up, Bryan wrote...

"I scared myself when I went to start the car after pressurizing the fuel lines, because the car wouldn't start, but the car just needed to work the air-bubbles out of the fuel rail or something. After cranking for a few seconds, I let the car rest for about a minute. Then tried again, and it started.... Tho it ran VERY rough, and was shaking. Probably working air out of the system, as I shut it off, and restarted, and it ran as smooth as butter."

He doesn't say anything about high RPMs, but I hope everything is good!

P.S. Oh, yeah, no paper T-stat gasket Rick!

You may have to take it out for a good steady run on the highway for a while as well as some around town driving.
Vary your driving style a bit and give the computer some time to average out and keep checking fluids then do another oil change to be safe. I bought some of the house oil (inexpensive) and a AC Delco filter for the first 50 to 60 miles. Then I changed to my regular oil after that.
Double check all your vacuum lines, etc. You should be good to go.
Glad you got it done.

BMD wrote:

P.S. Oh, yeah, no paper T-stat gasket Rick!

Good boy!

Hmmmm, when I've started the car today after a long while, the RPMs are high and eratic and remains so until a few minutes of driving. When I've started the car while its still warm, the car idles better, but still not consistantly. Vacuum lines look good, and no leaks so far. I'm gonna take her out for another boot, hopefully it helps, anyone have a suggestion?

I would double check that all vacuum hoses were installed properly (did you mark them before dis-assembly).
Check that the electrical connectors to the IAC and EGR are good and making proper contact.
Basically go over everything you removed or disturbed to do the job and verify again that all is good. Look at the vacuum lines that run under the SC and to the rear of the engine.
You may find an electrical connection on the IAC not right.

Hopefully you'll find something out of place or hooked up incorrectly as this is not normal, obviously.

sounds like a vacuum issue to me. did you just visually inspect the lines or did you spray them down?

All vacuum lines were color coded with stickers prior to disassembly and any broken vacuum lines were replaced with replacements I picked up at a salvage yard. Rick, where is the IAC located?

It's on the throttle body. Has a 2 wire plug on it.

Specifically, here's a factory diagram:

I figured it out . It turns out that the vacuum line ( indicated in red below ) which goes to the transmission, wasn't seated properly. It had a 1/4 of an inch to go, so I slid that up tight against the throttle body, and the surging stopped (phew)!

So I can now say that the job was a success, and it feels good to know that hopefully I am safe from any internal leaks for awhile. There was oily mud in the cavities in the rear of the Intake and down the block, where I obviously had a valve cover leak. So, now the motor is nice and clean and dry and it looks better than when I bought it. I must stress that whoever does this, you will crack atleast one vacuum line, so find alternatives before removal. Also, if you're planning to do your valve covers, now is a great time to do it. I have some pics that I might post, but the GTP write up is still essential for the first timer. Anyway the car runs great now. Thanks for all the help guys.

told ya

Is this a common issue on the 3800 motor? I ask because I popped the hood earlier to check my oil and noticed it's got a little leak. I've not had to add any coolant but it is just a tad low.

I currently have a 3400 motor tore down because of a LIM gasket, changing the head gaskets and having the heads rebuilt. The 3800 motor appears to be a little easier to work on as far as space goes.

Very common due to the composition of the early design gaskets. How many miles do you have on it.?
I just had mine changed for preventive maintenance at 112K miles. I didn't think they were leaking yet, internally or externally, yet when we pulled the LIM and got a good look at the gaskets it had appeared they were either on the cusp of failing or were already ingesting some coolant internally. A small amount but still something and I'm glad I did it when we did. I am also told there is a new SC gasket made out of aluminum that is superior to the paper and silicone gasket made by Fel-Pro but wasn't aware of it until after buying the GM gasket. I'm not worried because that gasket is not a known failure item. I did tap and plug the coolant ports in the LIM to Throttle body passages to eliminate the flow of coolant through those ports and that's supposed to help in a couple of different ways.

The 3400 you can buy the updated aluminum gaskets from the local auto parts stores, I know companies like Fel-Pro are providing the 3rd or 4th generation gaskets to customers and shops.

But for the 3800, as far as I know you can only get the aluminum composition lower intake gaskets for the supercharged engine from GM. I tried ordering the Fel-Pro's for my engine and they weren't the same as the GM's.
Just a heads up. I don't know what's available for the Non SC engine, I think those you can get the better quality from the parts store and Fel-Pro.

Much has been written on this site and others regarding these gaskets and small mod's that can help along the way. The types of sealants used are critical if you ask different people, etc.

If you are going to do the LIM gaskets on your 3800 there are part numbers for all the gaskets listed on here under the "Write Up" for LIM gasket change as well as some pic's of the tricks and changes to do.
If you are definitely going to do this job and have figured out the drilling and tapping of the LIM to prevent coolant flow to the Throttle body and that is something you definately want to do, let me know. I'll send you some 1/8" NPT plugs along with the instructions for buying the drill and Tap to do the job.
Rick

Yep. It's not necessarily a 3800 problem, but more of a mid-90's through 2007 GM V6 problem. Almost every 3.1, 3.4, and 3.8L had LIM problems. The 4.3L only puked oil from the Rear Main and the Front Crank seal.

Hell, every GM V6 has leak issues. The new(er) 3.5 and 3.9L's blow the front Crank Seal. I don't know why GM has such a problem keeping oil/coolant where it needs to be

Rickw wrote:

Very common due to the composition of the early design gaskets. How many miles do you have on it.?
I just had mine changed for preventive maintenance at 112K miles. I didn't think they were leaking yet, internally or externally, yet when we pulled the LIM and got a good look at the gaskets it had appeared they were either on the cusp of failing or were already ingesting some coolant internally. A small amount but still something and I'm glad I did it when we did. I am also told there is a new SC gasket made out of aluminum that is superior to the paper and silicone gasket made by Fel-Pro but wasn't aware of it until after buying the GM gasket. I'm not worried because that gasket is not a known failure item. I did tap and plug the coolant ports in the LIM to Throttle body passages to eliminate the flow of coolant through those ports and that's supposed to help in a couple of different ways.

The 3400 you can buy the updated aluminum gaskets from the local auto parts stores, I know companies like Fel-Pro are providing the 3rd or 4th generation gaskets to customers and shops.

But for the 3800, as far as I know you can only get the aluminum composition lower intake gaskets for the supercharged engine from GM. I tried ordering the Fel-Pro's for my engine and they weren't the same as the GM's.
Just a heads up. I don't know what's available for the Non SC engine, I think those you can get the better quality from the parts store and Fel-Pro.

Much has been written on this site and others regarding these gaskets and small mod's that can help along the way. The types of sealants used are critical if you ask different people, etc.

If you are going to do the LIM gaskets on your 3800 there are part numbers for all the gaskets listed on here under the "Write Up" for LIM gasket change as well as some pic's of the tricks and changes to do.
If you are definitely going to do this job and have figured out the drilling and tapping of the LIM to prevent coolant flow to the Throttle body and that is something you definately want to do, let me know. I'll send you some 1/8" NPT plugs along with the instructions for buying the drill and Tap to do the job.
Rick

I've got right around 200k on the car. Mine is a SC 3800. I'm probably going to pick up the parts soon and tackle the job sooner than later.

I used the newer metal LIM gaskets on the 3400 motor I'm working on. I also considered the throttle body bypass on the 3400, although it's only a matter of hose routing. Don't think it's something I'm really interested in. Do appreciate the insight though.

Was there ever a class action about the plastic gaskets and the L36's plastic UIM?

And yes the LIM problem is all too common in these otherwise awesome engines.

deekster_caddy wrote:

Was there ever a class action about the plastic gaskets and the L36's plastic UIM?

And yes the LIM problem is all too common in these otherwise awesome engines.

There was a class action regarding the LIM gaskets. Not sure about the UIM.

manofmany wrote:

deekster_caddy wrote:

Was there ever a class action about the plastic gaskets and the L36's plastic UIM?

And yes the LIM problem is all too common in these otherwise awesome engines.

There was a class action regarding the LIM gaskets. Not sure about the UIM.

Hmm. So will GM replace OE LIM gaskets on 3800s? I'm going to have to research this a bit and find out what happened there. When I have some "spare" time, which is rare for me these days.

deekster_caddy wrote:

manofmany wrote:

deekster_caddy wrote:

Was there ever a class action about the plastic gaskets and the L36's plastic UIM?

And yes the LIM problem is all too common in these otherwise awesome engines.

There was a class action regarding the LIM gaskets. Not sure about the UIM.

Hmm. So will GM replace OE LIM gaskets on 3800s?

Nope...

The settlement was for a $50-800 reimbursement of past repairs made within 7 years of manufacture, filed by last year.
http://www.girardgibbs.com/dexcool.html

So i noticed oil in my coolant reservoir today. I went to the shop to get a pressure test and and surprisingly(to me)it held pressure pretty well. The mechanic showed me coolant and oil down by the bottom of the manifold. I need a new lower intake gasket.


If I get it fixed the quote was for the new aluminum gasket, valve cover gaskets while he's in there, coolant flush and an oil change.
Doesn't it seem strange that it holds good pressure even though the gasket leaks? Even if I decide to keep the car and and shell out the $700 aren't I taking a risk if coolant is already in the motor? What would you guys do and have any of you had a similar experience?

Short answer: fix it.

Long answer: you already know the car and its quirks. A different car in this price range will have different quirks, as likely as not worse than yours (that's why they are selling it, natch). And check your dipstick - odds are you have no coolant in the oil, if you do it will most likely show up on the stick as foam or water drops.

Albertj