Welp, later this week gonna sample and drain the 5w40 HDEO from my TDI and pour in a 0w40 PCMO that's built for Euro sparkers and Euro compressers.

My short 10 mile commute (with the Interstate just 0.1 miles away) and winter temps convinced me to try 0w40. No A/C access for my coolant heater.

If I like it, I might use 0w40 year-round, though I have a few 0w40 HDEOs that could be options over PCMOs.

no guarantees that at your ambient temperatures, the 0w-40 will actually be thinner/flow better than the 5w-40. At -35, perhaps. At 0, I cannot say...

Im noting this now with GC. Ive always run an A3 spec oil, but it must be more viscous at the intermediate temperatures that I start at. This causes me to see a net MPG reduction, which is worse for the first 15-20 miles of driving.

I look forward to your findings.

Just make sure that the 0W40 you choose is specced for your model VW TDI, especially if it is one that requires 505.1.

I thought of that, as the temps here in Indiana don't get below 20*F in the winter usually, and rarely below 0*F. I used this thread as reference as part of my decision:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=158196

It is, I have an older TDI that can use VW 505.00, API CF-4 or ACEA B3/B4. The several 0w40s meet some or all of those specs.

The only PCMO 0w40 available over the counter at most auto parts stores such as Autozone, Kragen, Pep Boys and Walmart is M1, is it the one ?

Yup, M1 0w40 going in, but Redline 0w40 is another PCMO option. There are HDEO 0w40s from Esso and Petro Canada.

I forgot to mention the other 0w40 PCMOs from the various Euro oil makers: ELF/Total, Lubro/Liqui Moly, Pentosin, Motul. Oh and Royal Purple too.

M1 0w40 goes in tomorrow along with a Hengst oil filter (first time using those)

Will also do VOA on it, and UOA on the older DEO that's coming out (of the sump).

Well it's done. I'll sample at 5K and see how it's doing.

Initial impressions (ambient temp was 32*F/0*C and the car had been sitting for 16 hours overnight).

Much less lifter clatter (it's a different clatter than diesel combustion clatter) and faster engine warm-up (<---- not sure how that could be).

Tonight I'll find out if I can tell any difference during my normal 10 mile commute.

FWIW the girl at AutoZone who poured my used oil (5w40) into the oil recycling container said it was between water and syrup for consistency. The used oil container had been in the car overnight also.

Now that I've driven my 10 mile commute a few times, seems to warm up faster, have a bit more pep and no change in combustion clatter. Cold starting is much easier/smoother also.

Quicker engine warm-up (based on monitoring coolant temp) is interesting. You'd think it would draw off heat better than a 5w40, leaving less heat to transfer to the coolant. On the other hand, the water/oil heat exchanger function might be working better?

What prompted the change, Bob Fout? I recall a few months back you had compared old and new formulations of DEO. Did DEO not meet your expectations? Were you having issues with the DEO?

I had no issues with DEO (that I know of). The past UOA results were always good. Sample was sent today to B-stone of what was in the sump (3/4s highway, 1/4 short, cold trips). I'll see how those results are.

Starting 3 months ago, my driving went from mostly highway over long distances (800 km one way) to short (16 km one way, 8 km Interstate, 8 km side highways), cold/cool trips (-10C to 10C) with the Interstate right next door. I also don't have AC access for my block heater.

The coolant was barely reaching 90C by the time I got to work/home (who knows what the oil temp was) and with a cold engine went from home/work immediately to 90 to 110 km/h.

I wanted to see if a 0w40 oil had any tangible benefits in these conditions over a 5w40. I chatted some with Mr. Hillary about 0w40 vs 5w40 and ACEA vs. API oils and decided on M1 0w40.

In the future I may try out other 0w40, 0w30 or 5w30 (all Euro or API of correct specs).

So....I was chatting with Mr. Hillary about visco, and got I bored with an online visco calculator and started geeking out. And then this happened