Originally Posted By: Audi Junkie
You're attributing .1cP lower HT/HS of M1 AFE to an increase in fuel economy, while ignoring the significantly lower kinematic visc of PP that is as much as HUNDREDS of cSt THINNER from cold start thru +100c and beyond.
I call bovine feces on that, unless you can provide a reference to support your "HUNDREDS of cSt THINNER from cold start thru +100c and beyond" claim. Amusingly, that would give PP 5w30 a
negative viscosity in the 100's of cSt range. Quite a trick, that. (And may I say that the profanity filter on this board positively farcical.)
However, there is an actual mushroom growing in the feces. And that is that at 40C and 100C PP 5w30 does have slightly lower KV. Let's put some information up for convenient reference:
KV 40C (cSt) - M1:63.1 PP:57.5 -9%
KV 100C (cSt) - M1:11.0 PP:10.3 -6%
MRV - M1(-40C): 11,100 PP(-35C): 14,800 +33%
HT/HS(150C, mPas) - M1: 2.99 PP: 3.1 +4%
So PP is well over 33% thicker when very, very cold, about 9% thinner KV at 40C (104F), 6% thinner KV at 100C (212F), and 4% thicker at 150C (302F) under high shear conditions. Let's just dispense with the -35C to -40C performance, because I already know what you are going to say. And I pretty much agree for most locales.
The HT/HS number is known to dominate the friction equation after the engine has warmed up. As an example (and I can find more of them if you like) I submit this an
except from "High-temperature, high-shear (HTHS) oil viscosity: Measurement and Relationship To Engine Operation", James A. Spearot.
You can safely skip to page 53 if the link doesn't take you there. This is a *really* good paper, BTW. You might want to read it all.
So clearly, HTHS is the dominant factor in a warm engine. And if you want to dispute that you are going to have to produce a credible study that contradicts my reference.
But what can we say about a cold engine, or one that has not reached operating temperature? Unfortunately, not much. There is no reason to think that the HS behavior does not dominate at lower temperatures, as well. (Consider the amount of energy being dissipated by the oil pump, where the KV value will dominate, compared to the bearings, and in particular, the rings against the cylinder walls, at low temperatures, where the HS value would dominate. It's hard to imagine that it's much.)
Unfortunately, we don't have much information to work with. HS is only readily available for a warm engine. We just don't have enough information to guess what it is at lower temperatures, except to say that it no doubt increases drastically, like KV does. Likely much more than KV does, since VI improvers do not play a part in it.
It might be tempting to try to use the 40C KV value to make some guesses. But we already know, from the study linked above, the pitfalls of that. Especially since the 0w30 is so much thinner than the 5w30 at very cold temperatures. At what point do they cross, I wonder? I would say that this is, unfortunately, too shaky ground for us to say much about performance during warm up.
So basically, the 0w30 would be expected to produce slightly better fuel economy in a warm engine. And we can't really say much about a cold one.
Fortunately, this situation still satisfies me, pretty much, because a typical drive for me is to get in the car in Oklahoma City, OK, drive, and then get out at a Motel 6 in Albuquerque, NM, 550 miles away. Maybe stopping for gas once.
Quote:
Just checking.
I'm wondering if the above might take the "smirk" off your face. My guess is that is won't. You'll likely just ignore all this and proceed blindly on with your Mobil-Hate campaign. Which is fine; I don't really care. Both M1 and PP are good products. And writing this up has been of great benefit to me, in and of itself.
