1997 bonneville 3.8 non turbo. PO was about to sell it to junkyard when I picked it up off him. PO was driving fine until driving with low oil heard a loud pop, overfilled the oil and it started blowing tons of smoke later.

Suspecting blown rings I've gambled on UIM LIM gasket replacement. LIM looked good. UIM gasket was slobbering oil on outside of engine and wet oil tracks where noted on inside of intake valve ports. removed 1/2 liter of oil from under UIM sitting on the UIM gasket. EGR stovepipe full of oil dumping oil into UIM. I replaced the PCV and made sure its got gaskets and all good.
replaced LIM and UIM gaskets and removed the oil from the EGR and made sure its not stuck opened and clean. Removed enough oil to dip stick hash marks and started it. It smokes thick with blue tint. I ran it for maybe a minute seeing if it would clear up and shut it down. Started it again to see if it cleared up 12 hours later. Initially no smoke but after 30 seconds it began with a little smoke then started dumping the heavy smoke again.

My problem is similar to https://www.gmforum.com/1992-1999-91...l-help-304201/

except there was no resolution in that thread except maybe changing the oil

Can coolant thin the oil enough to let it slip passed the rings? Ive taken the UIM back off and noted maybe 3 ounces of oil again in the UIM from maybe 3 minutes running and again the EGR stovepipe is full of oil. I may be hearing a slight metal on metal note when running. I cannot do a compression test because warming it up requires smoke so thick its a hazard to traffic (mechanicing on street curb) at this point I`m diving down to rings to see if one snapped or cracked piston, scored cylinder wall or cracked piston lands. I cannot figure out why the EGR is full of oil though. The smoke is 100% of the exhaust, meaning as thick as it can get leading me to believe something is horribly wrong. I also noted a small amount of metal dust in the 1/2 quart of oil I removed from the oil pan.

My next step it to drain the old oil and compare viscosity to the proper oil weight. The old oil has 15k miles on it. I did not change it because I suspect cylinder damage and would have to immediately dump it to go after the rings. Not a fan of dumping brand new oil.

You should have changed the oil from the get go.

Well, for one thing, you overfilled the oil? You don't say how much?

It'* quite possible, your exhaust is full of oil...if it is, when the EGR opens, it could be sending oil back into the intake......thus adding oil to the lower intake recessions, and because there is oil in the exhaust, it'* going to smoke until it all burns up....

I decided to rebuild it looking for a cracked ring or piston. It looks like the problem is stuck oil rings gummed up with crud. I initially compared oil viscosity from the old oil and new oil and they where similar, thought about what Tech II said and decided oil slipping passed the rings would be sucked up through the EGR by the intake vacuum. Knowing this I might have tried throwing some kerosene through the spark plug holes or spritzing water into the intake with the engine hot to free up the gunk collapsing the oil rings. But the gunk (which is deposited throughout the oil train) is obviously combustion soot entering the oil train through bottom end blow-by due to worn compression rings, So it was time to replace the ring set and clean the oil train.

Tech II, I may have dropped a quart between rectifying the oil level and removing the oil from the upper plenum.

Mike, I gambled the cost of the oil change from not wanting to dump new oil before ripping down the engine. I'd say I gambled correctly since the smoking issue wasn't related to the LIM. If I noticed a major viscosity difference compared to fresh or changing the LIM and UIM gaskets stopped it smoking I would have continued with an oil change. I`m also not sure where the get go you where implying would be.

Rebuilt and reinstalled the engine and It still smoked like a freight train. Absolutely no improvement. This covers all my bases of smoking on the L36. LIM,valve guides, rings.Checked the new oil and it'* black with metal shaving from a few minutes of idle. Upper intake has a new liter of oil sitting on it. Compared that with transmission fluid and it'* too close to call on whether it'* oil or trans fluid.

Disconnected the transmission vacuum modulator and the oil cap after blowing on the LIM hole where the PCV hooks in to insure it had flow and draining off the oil under the upper plenum. Started it up and was able to get it to burn the smoke up and stop smoking.

I`m 90% sure now it'* the diaphragm on the transmission vacuum modulator and should have checked this from before the LIM change. I`ll pull a vacuum on the modulator and see if oil sucks out and replace the modulator if so. If not I`m Installing a filter as a crank case breather where the Oil cap goes, check compression and run it hard and possibly use the bon ami trick if I`m not getting good numbers.

I`m not ashamed of the rest of the work I put into this because it was driven to death and all of the work needed to be done. but nothing fixed the smoking issue.

The continuation of this thread is for the next guy that comes here and the only answer he finds is leaking LIM. I`ll keyword L67 Buick Le Sabre Park Avenue Regal Riviera Chevrolet Camaro Impala Lumina Monte Carlo Holden Commodore Caprice Ute Oldsmobile 88 Intrigue LSS Regency Firebird Grand Prix Monaro for that guy.

The cat converter can hold a lot of oil.

Trans oil smells far different than engine oil. Even tastes different.

Mike, how many times have I told you not to eat that stuff?

Uh, well...I know...several times. BUT it tastes soooo good.

It was the modulator, I don't think much if any made it into the cat. The trans fluid and oil where both burnt so it was hard to tell based on smell or color. The fresh oil I just dumped was obviously 2 oils mixed together

My bad, I thought '97 had a 4T65e(no modulator)....they still had the 4T60e......