Sorry that you feel it is cynicism. My intention was just observing the irony, mostly to do with perceptions of people who might not understand as deeply as you do.
OK, that's good to hear you are interested in honest engagement, I wasn't getting that sense reading your replies.
Yes, as with any complex topic, it tends to get grossly over-simplified and conclusive statements made that don't really reflect reality.
It's true that for the longest time most Euro mills spec'd an oil with an HTHS of 3.5cP or higher. There were many factors in this decision and many of those factors still apply to high performance engines that continue to spec oils of this style. The risk is that oil temperature will be able to get high enough that this becomes important. With oil temperatures properly controlled, many Euro engines are now spec'ing grades more similar to what we are used to seeing in North America. Also, I think concerns about high speed autobahn runs may be less of a focus now too.
On the other hand, there were many, MANY engines back-spec'd to 5W-20 and even 0W-20 that originally called for 5W-30, so from a ~3.0cP HTHS to ~2.6cP HTHS. This was obviously tested to be safe but there's been some questioning of the suitability of these recommendations which is likely some of what you are alluding to.
The "Honda Paper" that Shannow shared on here years ago spoke about the testing Honda did with existing engine designs and going thinner than the 2.6cP HTHS found in the then standard xW-20 grade. They found that this approach necessitated design changes, such as wider bearings, in order for wear to be maintained at an acceptable level. They were testing with 0W-16, 0W-12 and 0W-8. Additional problems at the time were that the base oil viscosity was so low that these oils wouldn't pass the API Noack volatility testing, so exceptions were granted to them. I have an old slide from one of the presentations on these from SK, the makers of Yubase, it was pretty wild how high some of them were.
What's often stated on here is that going heavier is of no detriment. This is correct, if you run 5W-30 in an engine that spec's 0W-16, you don't risk doing anything other than negatively impacting the fuel economy a bit. There have been identical engines that spec'd 5W-20 and 5W-50 depending on the vehicle they were fitted to.
On the other hand, there IS risk of going considerably thinner. Dr. Haas recently ran an oil labelled as 0W5 with an HTHS of 1.58cP, a grade that doesn't exist in J300, and this is an engine that spec's 5W-30. This produced visible metal in the filter, not good. Would he have had this problem with a 0W-20? Doubtful. He took an engine that wasn't outfitted/equipped to handle an oil with an HTHS
There are a few other factors that often get brought up:
- Fuel dilution
- Mechanical shear
The former is a much more common issue with the rise and seemingly ubiquitous nature of DI. This drives down viscosity and the response, by some, is to run a heavier oil to offset that. Seems logical. Of course the OEM must have done testing and accounts for some of that in the design, but, particularly with some Honda products operated in cold climates, it can get REALLY bad, and I think there's merit to that approach in those applications.
The OP on the other hand, has an ideal driving profile in a very moderate climate and he's using an engine already setup for an oil below that 2.6cP HTHS level. No real risk here IMHO.
