2011 Golf TDi:
I became disillusioned with Castrol back in the Hydro-cracking days - when I figured out that SynTech wasn't really a synthetic oil.
For some odd reason, I sent my oil out for analysis at the 30k OCI. This was probably because my free maintenance expired prior under the time portion, and I changed my own oil.
What I found was somewhat alarming - seems there were elevated wear metals: Iron was shown @ 88, Aluminum @ 20.
Blackstone's comments as follows: "We're glad you weren't dead-set on extending your oil interval, because we probably wouldn't recommend it this time, given the high level of iron we found here. Iron is from steel parts, and it typically tracks with oil use. Since averages are based on ~8,600 miles of oil use, we'd expect to see a lower-than-average level of iron on this shorter oil run. This could show excess wear at steel parts, although with everything else looking good, we're not ready to call any major issues yet. The TBN is good at 3.5, but stick with ~5,000 miles next oil to monitor."
So, I did some research, and found that a few other owners had posted similar result. And yes, I sent the Castrol LL03 to the great recycle bin @ The Zone with only 500 miles after reading the report.
Same time, I decided to give Mobil 1 ESP 0W-30 a whirl. I also installed a magnetic drain plug. Oil analysis was rerun @ 35k OCI.
I suspected that the magnet would reduce the iron content at time of analysis - but was really surprised that aluminum content had been greatly reduced. The results: Iron @ 19, and aluminum @ 6.
The next plunge - I decided to run Mobil 1 0W-40 at the 35k OCI. I like it, but feel it is too heavy for the 2.0 CR TDi. My engine doesn't seem to spin up as fast. And on a recent 400 mile jaunt, my fuel economy dropped from 42-3-ish, down to 34 mpg at normal interstate speeds - and then previously I had achieved 38-40 mpg @ sub-warp speed.
I certainly have no concern about the 0W-40, but I am returning to the Mobil 1 ESP 0W-30 at next 5k OCI - which should be 40k. I am undecided if I will have the 0W-40 analyzed.
If you have not done oil analysis, and you value your car's engine, highly recommend you give some consideration to the Mobil 1 ESP 0W-30.
For some reason I can't post the Blackstone image - not sure why.
Good luck.