I have a 1990 760 Turbo wagon AT. The coolant overfill is filled with what looks like soft peanut butter. The oil in the engine is clear. Does not overheat, and we have had oppressive heat here.

Anyone familiar with this?

 

Maybe the Transmission cooler in the Radiator split and is putting trans fluid in the coolant.

 

I will check that out. Thank you for your help.