Motul's message is that there oil promotes better mileage because of its lower HTHS. Everyone around here appears to think a higher HTHS is a good thing. So is resistance to wear at higher temperatures bad for gas mileage? Is their ester based oil so good that you can run with a very low HTHS and get protection and mileage, too. And by the way, they did not list their HTHS numbers, so anyone know what they are?
HTHS
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Does that message apply to all grades?
The question is lower HTHS compared to what? A typical Euro engine oil?
The statement, "lower HTHS promotes better gas mileage", is probably supported by the fact that the GF-4 fuel economy test has made the 3.0 to 3.1 HTHS range very popular for 30 weight oils displaying the energy conserving starburst emblem.
The statement, "lower HTHS promotes better gas mileage", is probably supported by the fact that the GF-4 fuel economy test has made the 3.0 to 3.1 HTHS range very popular for 30 weight oils displaying the energy conserving starburst emblem.
If you check out RL data it seems their HTHS numbers are always much higher than other syn oil. Yet, they claim that their fuel mileage is better, which in my Buell, seems to be the case (M1 vs. RL).
Interesting!
Interesting!
I guess that the implications of the HTHS rating for an oil are not understood by anyone on this forum. It is interesting that Motul, an oil with a good rep, it talking up lower numbers for better mileage. Maybe bigger numbers are not always better numbers.
Lower viscosity and lower HTHS #s go together, most of the time.
It is the thinner viscosity that allows better power and mileage, and the lower HTHS is a byproduct.
It is the thinner viscosity that allows better power and mileage, and the lower HTHS is a byproduct.
So, in general, with a good quality synthetic oil a lower HTHS is better?
A couple years ago, I kept asking the question on whether measured viscosity or HTHS was the major factor in economy (intuitively HTHS should be the biggest influence on economy).
Answers were wild and varied, but came down generally to use the thinnest oil with the highest HTHS.
Not sure that I agree.
Answers were wild and varied, but came down generally to use the thinnest oil with the highest HTHS.
Not sure that I agree.
You don't like dino 5w30 then?
So we should be using Redline 5w20.
Check this out for HTHS related to Motul 8100 products:
http://theoildrop.server101.com/forums/s...ge=1#Post801323
Regards,
paul...
I think it depends on the application/engine. An ACEA A5 (low HTHS) is great for many/most vehicles; An ACEA A3 (higher HTHS) is best for others.
HTHS viscosity isn't voodoo. It's the viscosity at 150C temp and a certain high shear rate which is more typical of conditions between certain parts of a warmed up engine than the viscosity at 100C and very low shear rate (flow from gravity). The oil between certain engine parts gets heated by the shearing so that's why it's tested at 150C and not 100C. Viscosity of most oils varies with shear rate; exceptions are generally those without polymeric viscosity index improvers. The viscosity drops (temporarily) as shear rate increases when there are polymeric VIIs. Yes, lower HTHS viscosity reduces viscous friction but of course also reduces minimum film thickness between parts. How much HTHS viscosity you need depends on your engine, your driving habits, and your climate.
Good description, JAG. Let me just add that if you have sufficient HTHS viscosity for the engine, driving habits, etc, the oil that has the lowest Kinematic viscosity will have the lowest pumping losses assuming of course you have sufficient oil flow to all engine parts. Engine design will greatly influence all these parameters.
All thing being equal, fuel efficiency is inversely proportional to HT/HS viscosity, but it's not a linear relationship. Of course when you get too thin you start to have signficantly more metal-metal contact and wear goes through the roof.
Looking at it from the standpoint of viscous fluid flow, I think that the pumping losses may be related to 1/cube root of the HT/HS viscosity. As I recall, the drag associated with pushing a boat hull through the water goes up with the cube of the velocity and their may be some dynamic similitude between these two situations?
TD
Looking at it from the standpoint of viscous fluid flow, I think that the pumping losses may be related to 1/cube root of the HT/HS viscosity. As I recall, the drag associated with pushing a boat hull through the water goes up with the cube of the velocity and their may be some dynamic similitude between these two situations?
TD
The winner in a Prius economy challange and the next two high placers used Red Line 5w-20 and it's HTHS rating is well over 3. Motul is advertising low HTHS ratings but what they are I don't know. I think Motorcraft 5w-20 is 2.6 or 2.8 and it's in a lot of Prius cars we cover in fleet maintenance.
There's a lot more to an oil's performance than just HTHS as related to hydrodynamic lubrication. There's also boundary, mixed, and elastohydrodynamic lubrication regimes to contend with.
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