Oil in Water

[allaninorlando]

I have small globs of oil in my radiator expansion tank. How did this happen and what should I do now? It's a '96 BMW 328iC, 191K miles, runs great. This is the only real problem and I would really like to keep it for many more years.

[Jeron]

Hopefully it is coolant sludge rather than oil. If it is oil it is the head gasket.

You can:
change the coolant and see if that clears it is sludge and clears up
do a leak down test to see if pressure is getting into the coolant
pressurize the radiator to see if pressure/coolant is forced into the oil or cylinders

[allaninorlando]

Thanks, so how do I tell the difference? What I have is dark brown and oily.

[Jeron]

There are some pictures here:
http://www.pelicanparts.com/bmw/techarticles/E36-Coolant_Flush/E36-Coolant-Flush.htm

[allaninorlando]

Do you think I should use a "radiator flush" type additive to clean the system before draining and adding new coolant?

[Jeron]

A radiator flush would not hurt.

When I have used it I:
1) drained and filled with Super Flush and distiled
2) drained and filled with distilled
3) drained and filled with coolant and distilled

But thats 3 jobs, albeit easy ones.

If you are pretty sure it's sludge I would do the 3 jobs. If you think it might be oil in the coolant I'd just drain and fill with tap water until you can determine if you need a head gasket.