Oil Analysis results revisited
April 15, I got the results of an oil analysis I had performed on some used motor oil from my car. I just took a sample prior to the oil change, mainly out of curiosity, but also to create a baseline so I could experiment with a different oil.
The high nitration results were the only measured quantity that was outside normal values. I’m not exactly sure what a normal nitration level should be, but I searched the web for some answers. I posted the question on two forums, asking what could cause the nitration level to be “high”. The answer I got: the cylinder head could be running too hot, my EGR valve could be stuck partially open, or something related to my turbo.
The EGR was actually stuck open, giving an error code that I cleared with VCDS (VAG-COM). I cleaned the EGR and everything seemed fine. This is what I thought caused the high nitration.
Today, I got around to testing my radiator fans, which should come on when the AC is running. There are two fans, one larger fan on the driver’s side (left), and one on the passenger side (right), directly behind the radiator. When I checked to see if both were running (they should both be on), only the passenger side fan was operating! This may have caused the engine to run hotter than it should have, although the temperature reported in the cluster always showed 190F. According to others, the temperature in the cluster isn’t always accurate.
I ordered a replacement fan made by Febi/Bilstein, part number 6X0959455F. Hopefully I get it early next week, or tomorrow if I’m lucky and they ship from White Marsh again. The removal does not look too bad, and I can probably get the old fan to work again with some cleaning. The only reason I’m ordering a new one is the convenience of having a working fan. The new fan was $90 after shipping. Compare that with ~1 hour or more of messing around with a fan that may or may not work reliably again, and you can see that it all comes down to convenience. If I can get the old fan working again, then I’ll have a spare for the future.
In the end, I think the oil analysis was useful. Because of a single abnormal result, I focused on possible problems that could have caused it, and found two that I would not have discovered without the analysis. I’ll probably do the oil analysis regularly now, just to see if I can follow this trend and determine if I fixed the problem.
Now I just need to replace my alternator pulley, serpentine belt tensioner, and replace my supsension, and my car will be good to go for the summer. 
