1998 Buick Century I dont know

Hi:
Coolant in the oil usually indicates a bad headgasket or intake gasket. Check it yourself. When you remove the dipstick to check you oil, is there a white foamy build up in the oil? Also, remove the oil fill cap and look in the engine for white creamy substances there and on the cap. If you find it, chances are there is a leak.

Let me know what you find, and we'll go from there.

Joe