I have a 2003 Buick Century w/V-6 engine w/77,000 miles. I'm getting a small amount of oil-water emulsion (soft brown paste) on the inside of the radiator cap. From looking at the expansion tank, it's been happening for some time. The transmission fluid level is fine and a nice red color. I'm assuming I have either a cylinder head leak or a leak of the transaxle fluid in the cooler inside the radiator. Any idea which one it is or an easy way to determine?

 

I have a '97 Park Ave that had a similar problem. Maybe this is your cheap and easy fix!


There's a plastic(!) elbow for the heater hose connector. It cracked and caused a small coolant loss and also apparently sucked in avery small amount of engine oil under certain conditions.I replaced it and solved both problems.


Hope this works for you.