Just bought a beautiful 03' Monte Carlo SS 3800 non-supercharged with 143k miles on it about two weeks ago. Car appeared to have no major issues, aside from it needing basic maintenance, and the lower intake manifold appeared to be leaking externally down onto the trans and to the bottom of the car. I didn't really want to do this job myself on my new car, so I talked to my local mechanic about him doing the job and he agreed, so I purchased the car and did my basic maintenance and handed it over to him to do it. Now, I will mention, before the gaskets got done, there was no coolant in the oil. I gave the car to the mechanic, and he did the job. I figured if the upper & lower manifolds were badly damaged, he'd give me a call and replace them, I never got the call, so I assumed everything was peachy aside from the old gaskets. Once I got the car back, the coolant puddles on the side of the engine were gone, so I drove it home, a couple miles down a 65MPH interstate. I let it sit, and I went out and checked my fluids because I'm a "worry wart" and it'* what I do. I noticed coolant in the oil. Called the mechanic and frankly chewed him out, he said all it needed was an oil change to get out all the "spilled coolant". So I took the car back on the 65MPH interstate to the local Walmart to get oil and a filter, drove back home. Changed the oil. After that, oil remained clean. This was Monday. On Wednesday, I changed the oil a second time, to just make sure anything left over was out. Oil has remained clean in my opinion, and had a different mechanic look at it, and he said it was clean as well. So as far as I know, the gaskets or manifold(*) aren't leaking internally. My question is, how damaged do you guys think my engine could be? It runs fine, no sounds or anything, and smooth. It had 25 miles or less put on it with the coolant in the oil, and has had two oil changes, one to get out all the initial coolant, and a 2nd to get out any remaining coolant.
Like I said, I'm a bit of a worry wart, so how badly do you guys think my engine could be damaged from the coolant in it?
Thanks!

Given that you caught it very quickly, I believe the likely hood of severe damage is relatively low. Most that have issues usually suffer internal leakage that is not detected until much later, usually when they run out of coolant, overheat, and then discover a nice chocolate milkshake in their crankcase. If it spins a bearing within the next thousand miles, it could be related. Beyond that, you should be out of the woods.

I am more concerned the mechanic didn't address it, which causes me to question what condition the UIM is actually in, and if it'* not the greatest, how much did it getting jostled around upset it. You can check manufacture date and usually determine what you are up against.

Thank you for your reply. I am considering doing the job over again myself at this point, this way I can see everything and I get the good feeling to know that I did it myself and that it was done correctly. I'm also tempted to do this because it is now, yet again, leaking from the lower intake manifold. Not a big leak, but one that leaves a small puddle of coolant on the transmission, and that'* a big no-no for me. So I think I'll likely go get a new UIM and redo the entire job myself.

I hate having to redo jobs like that. Oh well, if you are diving in yourself, make sure you get a sleeved UIM, metal framed LIM gaskets, and metal coolant elbow. Also, if you are feeling really adventurous, you may want to look in to porting while you are in there. I hear the L36 had a lot of casting issues, and responds really well to porting.

I would check that the throttle body gasket is not leaking first.....

Also, shame on the mechanic that did not do an oil change after the job....

I dang it may be a BLOWN HEAD GASKET, hope not..but that is how my luck goes

3800'* don't kill head gaskets.

The only known headgasket failures are associated with too much boost, or with an extremely negligent amount of overheating, and even then has an equal chance of cracking heads or seizing the block as well.

"With my luck" usually involves a fragged bottom end within the next thousand miles in this particular application.

Well it'* been a few hundred miles since the last oil change I'm sure.. haven't been keeping track but what I do know is that I've driven the car pretty consistently in the past few days, my cars get a lot of miles on them pretty quickly.. All seems well. Except for the stupid coolant leak from the lower manifold again, which is irritating. I was gonna just let the leak go for a little while until I physically had the time to redo the job again, but after looking at it tonight it seems to be growing so I'm gonna have to jump on it pretty quick. This is ridiculous. But there are no signs of more coolant in the oil, and the engine is running fine. Changed out the spark plugs and wires this morning, which were original plugs and wires, and that really woke it up, and also improved MPG amazingly. I want to say I'm in the clear for the lower end, but I've never had an issue like this so I don't really know.

Like I've said before, I'm a worrier about my cars and most things really. So in my case, "wishful thinking" is just unrealistic thinking. I always assume the worse so I don't get hope up for something that is very possible to happen. I know, I'm a bit of a Debbie-downer. In the last two oil changes, I've used Walmart Supertec oil as just a cheap oil to basically flush the system. Tonight I went and got good ol' Castrol oil, and will be doing the 3rd and final oil change (for this week). What should I look for in the oil? Metal particles in the oil would pretty much confirm future bearing problems wouldn't they?