Several months ago, I had a '98 3.1 Monte Carlo with 175K miles given to me by a co-worker. The intake manifold gaskets were failing for the second time (originally replaced by the dealer) and he was tired of the car being a money pit. I drove it home, verified that it definately had bad LIM gaskets and parked the car until I had time to replace them. About a month ago I finished up the repair with Fel-Pro replacements and refilled with G-05. I had about 7-8 quarts of a oil/coolant froth drained out of it that looked like a chocolate milk shake. Replaced the oil with 10W-30 Trop Artic (been some REALLY good sales on the stuff lately) and a NAPA oil filter and put about a thousand miles on it.
This past weekend I drained it, put on a SuperTech filter and some 5W-30 Trop-Artic and it has been a good looking, economical work car. The engine appears to be in good shape, considering everything that it's been through.
Anyway, about day after I changed oil, I cut the filter open and inspected it. Sorry I didn't take any pix, but there was probably about a teaspoon of black deposits inside the can itself. I did not bother to cut the media to inspect, but I'm sure it would have been pretty full also.
I guess the purpose of my post is to say that I'd recommend some oil changes that are a little more frequent after a LIM repair. I was surprised at the results. The next oil change will probably be about 2K miles from now to see how this is progressing.

I replaced the L-I-M on my 3.1 at approx. 80K before it ever got to the point where I noticed coolant loss. I did it as a PM because a UOA showed 'traces' of Potassium and I had been told that the L-I-M on all 3.1's and 3.4's eventually fail. I used the Fel-Pro problem solver, new bolts and additional loctite. The only mistake was that I used Prestone AMM which is a Dexclone.
It is a shame that GM allowed this POOR DESIGN to go on uncorrected which hurt their reputation severely. The poor design along with the gasket eating 2-EHA in Dexcool killed many 3.1's and 3.4's. It's a shame because this low-tech engine was economical and durable otherwise. (I have heard of several with over 300K and one with 800K ...but all had the I-M gaskets replaced...some several times. The guy with 800K told me it needed replacement about every 200K regardless of which brand gasket used.)

I've been a Ford man my whole life, so forgive the stupid question.....But the constant replacement will happen even if you use G-05 or the old-school green?

I'm a Mopar guy, but since no one else has answered....

The 3.1/3.4 LIM gasket problem is a sort of perfect storm. Its a weak gasket joint design to start with, and when you throw in DexCool containing 2EHA that further softens the gasket you have a high percentage of serious failures. Eliminating the DexCool softening of the gasket will cut the failure rate way down. Using a FelPro gasket probably takes care of the rest of the issue. The 3.1/3.4 wasn't a horrible gasket disaster before DexCool, so it should be pretty reliable without it. Its never been what you'd call a great engine design dating all the way back to when it was a 2.8, but its a journeyman. It usually runs a long time and gets the job done without a lot of fuss and bother. Not unlike the old SBC- nothing spectacular, but very adequate and inexpensive.

Just as a point of comparison, the first-generation Chrysler 3.5 (I had one for 260,000 miles) also tended to eat lower intake gaskets until a revised gasket came out. The difference was that it would just weep some (conventional) coolant which didn't further soften the gasket, plus the coolant went harmlessly outside the crankcase instead of into the oil. So you could run it that way a pretty long time just topping off coolant regularly without worrying about wrecking the internals. Besides, you'd usually be forced to fix the gasket due to a lean misfire on cyls 2 or 3 before the coolant leak became more than a weep anyway.

The 2.8 in my Dad's Pontiac 6000 ran like mint to 198,000kms without a leak or a slap. Two sensors failed, the alternator failed, ball joints, tie rods, exhaust and that's about it. Had it oil trell'd and Meguiarized - great car.

My Dad usually used Valvoline or Havoline, I can't quite recall, but to see the same basic design become fudged is the same reason why I'll buy a Ford or mayyyybe a chrysler before a GM.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1633430#Post1633430

pic of my acdelco filter cut open after intake manifold repair.

those new fel pro gaksets are great, much more well built than the ones that came with the car.

If you have an 05 or up 3.4. Like in the Equinox. Their intake is redesigned and it uses different gaskets.

I have the Dex Cool in my Trans Am, it has a dry intake, meaing no coolant in it. I also have it in my Supercharged 3800. It has different gaskets. So no issues there either. I have it in the 07 Equinox I own as well.

The key is to keep it full so you don't get air in the system. I change my radiator caps every year and flush the stuff every couple of years. I suspect that the Dex Cool plays a part in the failures, but lack of maintenance is good part of too.

Sorry I didn't get back to you sooner but 440 Magnum summed it up pretty well. The design is poor and the number of fasteners is insufficient. When you couple that with 'gasket-eating coolant' it's a recipe for disaster.

If you change the gasket using the Fel-Pro Problem Solver and use lock-tite on the bolts
and use a non- 2-EHA coolant (like Peak Global or GO-5) and you let the lock-tite and sealant set-up over night (which most dealers don't) there is a good possibility that you won't have the problem again. That is a lot of IFs.

Ls1mike does that mean that you replaced the factory plastic lower intake gaskets with the new aluminum frame gaskets?

Oddly enough the Supercharged cars did not have the probelem.
The N/A cars did. While it may occur it is rare. I believe it is due to the fact the LIM is aluminum and not plastic.
It is my understanding it is a different gasket. I may be wrong though as I have not had a supercharged car's intake off.
Either way the Supercharged cars didn't have a metal frame either. I wonder if the LIM just sealed better.

gasket failures have occured even in regularly maintained vehicles.

You mean like this kind of sludge?
Filter 1
Filter 2
This was after I did the LIM gaskets on a 3400. I ended up going back into to do head gaskets.
Headgasket

Ls1mike what radiator cap are you using on the Regal?

http://www.dex-cool.net/

Every set of 3800 II lower intake manifold gaskets look like the ones in the picture after six or seven years whether NA or SC. The SC manifold is stiffer and should not move around as much as the NA but the junk plastic gaskets are the same.

My opinion is that Dexcool will not eat the Felpro problem solver gasket. Dexcool doesn't deteriorate any and every gasket. I also think that once this problem-solver gasket is installed properly with new bolts and loctite it will not leak again, or at least have a slightly better life than most other V-engine manifold gaskets. I've never seen one leaking. Geez it was just a badly designed gasket that may or may not liked dexcool, the whole engine wasn't junk.

I use a 16 lbs cap.
I have had three 3800 supercharged cars all with over 160,000 miles on them (well except the regal it is at 65,000) and race with a bunch of guys that have them. I have not seen a S/C LIM fail like the N/A one have. I have never even heard it mention on the Big 3800 S/C sites. I hear about plenty of N/A failure though.