Oil in Antifreeze?

I have a 1999 GMC Jimmy, with a 4.3 motor. I had the radiator replaced last summer, with new antifreeze of course. (Also had the rad flushed)

Recently I seem to be getting a black oily film in the radiator overflow tank?

The oil level doesn't seem to be going to down. The engine also runs great.

Is this something to be concerned about?

Do you see any of this in the radiator?

My first thought would be to check for water in the crankcase. If there is none there then you could possibly have problems with the oil cooler in the rad. You can also have a competent radiator shop test your antifreeze for signs of combustion residue and that could also point of a possible head gasket.

I would personally drain the system, do a good chemical flush of the entire cooling system, including pulling the block drains, and refill the system to specs and see how it does. I know my cooling system did the same thing with the oil in the overflow and my personal issue turned out to be intake gaskets.

My first thought would be to check for water in the crankcase. If there is none there then you could possibly have problems with the oil cooler in the rad. You can also have a competent radiator shop test your antifreeze for signs of combustion residue and that could also point of a possible head gasket.

I would personally drain the system, do a good chemical flush of the entire cooling system, including pulling the block drains, and refill the system to specs and see how it does. I know my cooling system did the same thing with the oil in the overflow and my personal issue turned out to be intake gaskets.

My Money is on the intake gasket being bad. the 4.3 is famous for it. There is even a better gasket set out to prevent this from happening again. Took me 6hrs to fix mine.