transmission oil in the coolant
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1990 BMW 750iL Question: coolant oil leak
Answer #1patrick mannion from Greg Solow's Engine Room, April 29, 2009, 00:18Master
The 750 has a transmission oil cooler mounted in the radiator. Engine coolant is used to take heat away from the transmission oil. It is the most likely place foe transmission fluid and coolant to mix. Continuing to drive the car will destroy the transmission and damage the cooling system hoses.