97 grand prix radiator problem...

The temp. on my 97 grand prix was high so I opened the radiator and it looked like someone had filled the thing with mud. I took it to a mechanic who told me that it looked like the previous owner had put some stop leak fluid in and never flushed it out. He suggested that I replace the radiator and have the system flushed. I replaced the radiator and flushed the system out but the next day when I checked the radiator it looked like someone poured black water in there and now a few months later its back to looking like someone put a bunch of mud in there. What could be the problem? I used a radiator flush solution to flush the system when I replaced the radiator and I guess it didn't work my car still gets hot especially when I am in bumper to bumper traffic....can't figure out the problem.

I would agree that perhaps you are boiling the fluid due to a leaking headgasket(s).

However, I would discount the possibility of engine oil getting into the radiator or the cooling system for that matter...a pushrod engine has only splash lube to the cylinder heads (as opposed to OHC which requires oil pressure in the heads) and so there's no impetus to drive the oil into contamination with the coolant.

A much more likely scenario is that the coolant ends up mixed up in the oil pan...so I'd quickly do an oil change and see what comes out.

Not sure which V6 you have, either 3.1L or 3.8L, but sounds like head gasket or intake gasket leaking. When oil and dexcool coolant get mixed and "boiled" together it looks nasty. ;) I would reflush cooling system and have a pressure test done to determine if it's leaking. Being it got that hot you're more than likely doing head gaskets anyways. Good news: these engines are fairly simple to do a head job on so dont be scared away.

my grand prix is a 3.8L V6..

I would agree that perhaps you are boiling the fluid due to a leaking headgasket(s).

However, I would discount the possibility of engine oil getting into the radiator or the cooling system for that matter...a pushrod engine has only splash lube to the cylinder heads (as opposed to OHC which requires oil pressure in the heads) and so there's no impetus to drive the oil into contamination with the coolant.

A much more likely scenario is that the coolant ends up mixed up in the oil pan...so I'd quickly do an oil change and see what comes out.

I took it to an oil change place about 2 weeks ago, I don't know what the oil looked like....If its getting mixed in the oil pan does that confirm that the gaskets are leaking? If not what else could be wrong?

Check the tranny fluid level. Let us know how full it is and what color?