Oil weight

Jayman please post the UOA for that new Toyota mystery oil again.

 

Joe:

So in theory, a person who lives in a very cold climate who decides to run Mobil 1 0W-30 is at risk of voiding the warranty, because it's not a 5W-30.

I find it very interesting - and contradictory - that car makers here in North America are not allowed to specify different viscosity oils for different expected ambient temperatures, along with a "generic" choice.

For example, both Ford and Honda have determined a 5W-20/0W-20 are best for North America. In other parts of the world, the same exact motor can run up to a 20W-50, depending on expected ambient temperature.

Nobody has been able to prove there is something "different" about Honda or especially Ford and Daimler Chrysler engines, compared to say Toyota. Engine assembly clearances really haven't changed in +25 years.

For now I'll only use Mobil 1 0W-20 as a "winter" oil for my Prius. As I expected, there was a fuel economy improvement in very cold city driving (-20 C down to -35 C). During warmer temps, especially on the highway, there was no difference in fuel economy that I could detect.

You'll have to be patient for my used oil analysis though. I probably won't even change it until the end of the month, then will have to wait 1-2 weeks for the results. Rest assured, they will be posted. I'm just as curious about it as you are.

jay

 

Frank:

Here you are, big guy:

http://priuschat.com/High-Na-level-in-oil-...ved-t14829.html

jay

 

Is it possible that a slightly thicker grade keeps more oil on the bearing surfaces between the frequent starting and stopping of the ICE? Perhaps it's a trade off of reduced wear at the expense of an MPG or two?

 

Actually just the opposite. That's why Honda insisted on a synthetic 0W-20 for the Insight. A more viscous oil takes longer to pump up, but the slight difference in boundary film lubrication only matters at very high operating temps with severe shearing forces.

It's easy to prove that a thick oil causes substantially increased wear over a thinner oil, in conditions of frequent stop/start and especially cold temperatures.