I just wanted to THANK all the posts regarding LIM & UIM replacement. I have 99 - 3800 series II and was gradually losing coolant with an occasional ignition miss. Without the engine slightly missing evey now and then, i would not have known I was losing coolant. Mileage also went from 27mpg to 23 mpg. I replaced LIM gaskets with GM aluminum and UIM with a Dillion permanent fix. Car runs great and have been watching coolant level for 10 days... no change. The techinfo section is great. I followed instructions, no probelms. I can see where you could lose an engine quickly if not aware to observe coolant level or know there is a UIM problem with this engine. GM should have to do something about this. It isn't "if" UIM will fail... its a "when". Thanks Again to All!

You may be thanking us for the info...

Great job on the wrenching

Glad you caught yours and got it done in time! And you're right of course! GM should have at least acknowledged that this would be a regular maintenance item, say every 50,000 miles. That would not have obligated them to replace them free, but would have saved many a 3800 from hitting the scrapyard with an early death.

I see it as comparable to the classic Honda timing chain replacement at 50,000 miles.

Acknowledge and support...that'* all that needed to be done.

On another note, I should probably go ahead and buy my permanent replacement UIM and LIM gaskets to be prepared for my next change. Mine was done about 45,000 miles ago with standard dealership parts, not the good ones we now have at our disposal.

Its important to get the Dexcool out of there before the 5 yr interval as it turns acidic and eats everthing up. You should then be able to get a lot more than 50k out of it.

Excuse my ignorance, but what is "Dexcool"?

It'* the orange coolant that everyone hats, but no one has ever proved there is a problem with.

So you're talking about Antifreeze. Thanks MOS95B.

Thanks for the compliments on the wrenching! Not a hard job, maybe five hours or so if you stayed on it. I've worked on cars and boats all my life and it was pretty basic with the info provided from this site. Most time consuming was the cleaning of mating surfaces and my TB was carboned up pretty bad.
I used the new Prestone for my replacement antifreeze. It appeared the owner before me had changed over to prestone, Dex-cool was gone. The radiator and water passages were very clean. when looking in the radiator cap hole... the inside core area of the radiator has no deposits and as clean as a new one. I put a 180 thermo to replace the old 195.
Keep up the go work here along with the advice. My buddy here at work has a 96 Jimmy with a 4.3 (115K) and he told me his regular service guy told him he was losing coolant internally. Any of you GM guys know about this one?