1999 buick park avenue oil in antifreeze-how??
Possible head gasket leak or a leaking transmission cooler into the radiator.
Check the transmission fluid lever....also look for signs of water in the transmission. Since the transmission fluid pressure is usually higher than the coolant pressure, the transmission fluid get into the radiator. If you feel that is what is happening and you don't want to replace the radiator, add an auxillary transmission cooler and by-pass the radiator.
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