I brought my car to the mechanic to have the oil changed on a 2004 530i. When he opened the cap, it had yellow residue on the cap and around the rim of the opening of the engine cover. It seems like the coolant has somehow mixed with the oil in the engine. However, the coolant level in the expansion tank did is at the right level. If indeed the coolant mixed with the engine oil, what could have caused this? I now have only 51,000 miles on the car and it seems very premature for the engine develop such a malfunction.

A brief history of the car. I bought it pre-owned in March 2007 with 31,000 miles from the original owner. The original owner followed the minimal maintenance requirement as specified by the Idrive. In October 2008,at 42,000 miles, I had the fluids (engine oil, manual transmission oil, differential oil, power steering oil, and coolant flush). I used Red Line oil when applicable and BMW coolant and distilled water. The car has never overheated while I've owned it and I'm assuming it never did too with the previous owner since the dealer would have alerted me had it shown up in their diagnosis.

Could the change in oil brand (Red Line as compared to the BMW brand used while under warranty) have cause this residue and not the coolant mixing with the engine oil? I left the car with the mechanic since I'm afraid that if I drive it home while I read up on the problem, I may cause more damage to the engine. I've asked the mechanic to hold off on the repairs till Monday.

Thanks.

 

That sounds more like condensation and may be normal if your driving patterns don't include a regular dose of extended highway driving. Keep a close watch on your oil and coolant levels so you can catch any issues early.

 

i'm assuming you're talking about the oil cap. if you do a lot of short trip driving, excessive moisture can build up in the crankcase, and show a slight residue under the oil cap.
if you really want peace of mind, drain and change your oil, and inspect the used oil for water contamination. oil would look milky and frothy.

 

The oil cap is one of the upper most parts of the crankcase, so thats where the last of the moisture will collect before it's burned off. It's fairly normal. Pull your dipstick and look at the oil on the end of that. If that oil looks yellow & frothy, then you have a problem.

 

Yes this is completely normal for cars that see mainly short start-cycles. Go on a long trip and VOILA the sludge will be gone. On another note, this is kind of scary, as I've never had a BMW that did this, even one that saw a lot of short trips.

 

Thanks for all your feedback. I'm having the cooling system pressure tested. Hopefully, it's just condensation. It usually just goes 3 miles in the morning and 3 miles in the afternoon during the week. It's hardly used on weekends, too.