My 1998 Lumina LS overheated last yesterday, the gauge went from cold to hot and then back down again several times. I later looked under the hood after i pulled it off the road and there was a WHITE CREAM ON TEH OIL CAP, looked as if coolant was mixed into the oil, The WaterPump wont turn as then as i started the car. The Coolant in the resivour rose and became dark in color. I have no clue what happened and I havent moved my car since, any one have any suggestions and advice????