[dremd]

Quick story.

My Dad purchased an 06 Sprinter 87,000 miles, I changed the oil with Rotella T6 (same blue jug I run in my TDI). I pulled a sample at 10,000 miles and sent it to blackstone it felt fine, looked normal etc. A few days later I got a call from Blackstone asking what kind of top end work had just been done, iron was 136 (normal is 37, and my car runs around 40), Silicon was 33 (normal is 5 my car is 4) and aluminum 28 (normal 14, my car 4). I don't know of any work done to the van, but hey advised to drain IMMEDIATELY and resample in 2,500 miles. (he hasn't racked up that many miles yet).

Anyway, I tried a simple single blind test of "feel, look, and smell" for the 2 viles of oil (mostly just to verify that I could in fact look at oil as well as a typical mechanically inclined person). None of the 3 participants (nor myself) could tell them apart even though the Sprinter oil had at least 5 times the contaminants as the VW.

Seriously, looking, feeling, smelling is basically usless for metallic wear until you need a motor (your oil clearances are much smaller / smoother / harder than your fingers are).

You can detect Fuel in oil, partially by nose, and partially by putting a drop on a white paper towel (Diesel fuel wicks out farther than the oil), however fuel in oil is only one potential issue.

Another thing to check when extending drain intervals is your thermostat, running your oil (TDI has an Oil-> water heat exchanger) at the appropriate temperature helps evaporate the water out of your oil which can cause acid formation which in turn corrodes parts.

Best of luck to you, and seriously, there is a good chance that your oil is in decent shape, but how do you know.

Oh, BTW: my longest drain interval in my TDI was just over 60,000 miles, I drained it at timing belt change just because, the UOA still looked fine. I do have a Bypass oil filter and working thermostat, and I drive 20 miles each way highway several times per week (gets oil all the way up to temp). My oil consumption is about 1/3 cup every 10,000 miles, but I do have a leaky valve cover gasket, which accounts for some of that. My car has 238,000 miles just over 100,000 of that is with me owning it with a bypass filter installed.