Oil in coolant
 

It is a 1993 Cutlass with a 3300, NO water in oil. I thought I'd check and see if this is common and what the cause is . No smoke or oily exhaust pipe. I just dont want to tear into it farther than I have to. Thanks for any help, Mike

Only way I know that oil can get in the coolant without coolant getting in the oil is though the oil or trans coolers built into the radiator itself. Might want to check the trans oil.

OIl pressure is higher than coolant pressure. If the engine is internally leaking, it will push oil into the cooling system. Usually via the head gasket.

Thanks, I didn't think of the tranny cooler. If that isn't it I will pull the intake and heads trying to read the gaskets as I go.

Are you sure? If it is a small coolant leak it may not be detectable in oil unless you let it sit a couple of days then pull the drain plug slowly to see if water comes out first.

Not common on these. They hold up pretty well.

I'd go with what the guys said above ^^^^^^ . A few questions:

How many miles are on it?

Have you owned it and driven it for a while?

Any recent trauma?

How old is the radiator?

In what part of the world does this car live and work?

Can you pick out what color this oil is (in the coolant)?

It has 177000 miles. I saw moisture in the radiator cap a while ago. oil is clean so it's not my #1 [priority right now.

Like oil moisture?

Oops, I meant oil residue

Okay cool, makes sense because the oil floats to the top and the highest point is the radiator cap on this car.

By the time GM designated the Buick V6s as 3300 and 3800 (a lot of improvements,1989, IIRC), they were very solid engines. The 3300 is shockingly simple and robust for a very modern engine (circa 1989), even though it didn't have the best idle characteristics.
With that said, if there is any oil / coolant mixing on these engines, they have intake manifold gaskets that are nearly as pathetic as the better know issues with intake gaskets on Chevrolet engines (3100, 3400, and V8s). They are a similar plastic carrier and rubber seal around the points. They will slow leaking for a while, just like the Chevy's, from a little more torque on the intake bolts. Mine weeps oil out the corners. Going to change it soon.
This is the set for a 3300. I don't believe there even any improved designs available.


https://cimg6.ibsrv.net/gimg/www.gmf...d5cab0550b.jpg

I confirmed my suspicion about these gaskets today.
It took me an hour and 25 minutes from first disconnecting the battery (I had drained the coolant last night) to go from this;

https://i.postimg.cc/qNMQtK59/Before1.jpg

https://i.postimg.cc/5XxKwT6K/Before2.jpg

To this;

https://i.postimg.cc/w75bRgTs/After1.jpg

https://i.postimg.cc/ZBywbhMn/After2.jpg

As you can see, these gaskets are crap too;

https://i.postimg.cc/t7WB8p6m/After3.jpg

https://i.postimg.cc/7CRBrLXj/After4.jpg

IIRC, I've seen other 3300s that were machined front and rear for a counterbalance shaft. This one is only machined at the front of the engine.
https://i.postimg.cc/D8hxTHdf/After5.jpg

I'm suspect oil analysis would have shown a problem.

The displaced gasket surfaces were readily seen on the intake too.

https://i.postimg.cc/56mnNgnB/Intake1.jpg

https://i.postimg.cc/8F7H4SD4/Intake2.jpg

The clean up;

https://i.postimg.cc/YL68Fzkw/Clean1.jpg

https://i.postimg.cc/xk8sZmGK/Clean.jpg

Got to this point at 16:25 today;

https://i.postimg.cc/LJCDjXdh/Reinstalled.jpg

Finishing tomorrow should be easy.

Sorry I havent responded, other things had priority. I looked today and NO sign of coolant in oil or tranny.
I wish there was a sign of cross contamination. When running , oil and tranny pressure is more than coolant, but when you shut it off oil and tranny go to 0 and coolant pressure stays for quit a while.
I'll pull the intake next but I hate trying to "read" gaskets.
Actually as thick as the goo is I'll have the radiator flushed and checked first.

I think that's your best bet, and easier and less invasive than the alternatives.

Transmission coolers are usually on the return circuit, so they usually have less pressure than the radiator.

Does it have an engine oil cooler built into the radiator?

I drained the radiator a few times then added a heavy duty flush and let it run about 3 hours. Then I opened the drain and adjusted the hose to just keep it full while running for a couple more hours I will keep a close eye for oil again.
There isn't an oil cooler on this.

Did it have a lot of oil floating in it before you drained it?

Yes, lots floating and mixed with the coolant.

Black, brown, red, or undecided?

Black floating and the coolant was brown

Sounds like engine oil then, does it have an oil cooler built into the radiator?

Nope, no oil cooler

Ouch. sounds internal then. Maybe a head gasket. Has this engine been apart before that you know of?

Still, I'd pressure-test the radiator as a diagnostic step. If you find a leak between the transmission cooler and the radiator it might save you opening the engine up.

It's definataly not tranny fluid. I guess I'll wait till there is coolant in the oil, then I should be able to read the gaskets to see which one is bad.

Darn. Yeah besides blindly getting into the engine this might be the easiest way to find your leak.