MPG vs HTHS

J

JamusMcFamus

Joined
Sep 24, 2020
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Location
Columbia, SC
This thread is not meant to be about the pros and cons of high vs low HTHS. I’m purely curious as to whether the normal person would notice a difference in highway mpg between, say, Mobil 5w30 ESP, and Mobil 5w30 vanilla. Or even yet, some general 0w20.

I daily my 2017 Miata. I’ve used 5w30 ESP since new, and my 25 mile one-way commute is 95% highway. Not interested in changing oils, just a thought experiment. Better yet, has anyone measured differences in their own consumption?
 
JamusMcFamus said:
This thread is not meant to be about the pros and cons of high vs low HTHS. I’m purely curious as to whether the normal person would notice a difference in highway mpg between, say, Mobil 5w30 ESP, and Mobil 5w30 vanilla. Or even yet, some general 0w20.

I daily my 2017 Miata. I’ve used 5w30 ESP since new, and my 25 mile one-way commute is 95% highway. Not interested in changing oils, just a thought experiment. Better yet, has anyone measured differences in their own consumption?
Click to expand...
No one here could ever isolate that specific variable in every-day driving and come up with a conclusive answer. It’s deep in the noise.

There is a standardized ASTM test for this and that’s the only way you could come to a conclusion.
 
There are papers online if you look.

You asked if anyone here has measured it, so I answered you in that context. Unless they have access to the proper laboratory equipment and standardized test fuel then the answer to your question is no. Besides the vagaries of everyday driving the energy density of fuel is a large variable.

You also asked if two different formulations of the same grade could be determined and that's even farther into the noise.
 
I have a feeling that the mpg $ savings for the month is less than the difference between the price of one order of large vs. extra large drink at McDonald's drive thru.
Fries 🍟 are another story and no hths can compensate for that. Would you like fries with that?
 
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DemoFly said:
What leads you to believe a shear spec has an effect on fuel economy?
Click to expand...
Higher HTHS=more friction in the oil, a fractional decrease in fuel economy & increase in oil temperatures. I’m SURE the manufacturers have measured it, but unless ALL variables can be controlled, there’s really no way to test it, short of a treadmill, and holding everything constant. I guarantee hypermiling would give better MPG improvements than just dropping a grade.
 
I've seen posts on here where people don't see a MPG difference going from a 0w20 to 5w30. So I doubt there'd be a measurable difference between a high and low HTHS 5w30.
 
DemoFly said:
100%

Why would anyone consider an HTHS spec between two appropriate 5w30 oils for a passenger car on public roads and its effect on fuel economy?
Click to expand...
That pretty well defines what influences fuel economy. But I agree, two oils of the same grade is virtually inconsequential, maybe between an ILSAC and ACEA A3/B4 30-grade but still small. It's why we have 8-grade oils.
 
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OilUzer said:
If you have billions of cars, it will add up. Isn't that what CAFE is for?

One single car or even a family with 4 cars, you should look for a bigger fish to fry!
Click to expand...
A family with 4 vehicles, two of them teenage drivers , isn’t going to notice a 1 or 2% improvement in fuel economy which could add up to $20 a month.
That’s like a deck chair blowing off the Titanic. (Or me losing 20 pounds)

Let’s have a look at the new API FA-4 HD grade for OTH commercial trucks.
HD 5w & 10w30 typically have a hths of 3.5-3.6.
FA-4s have a maximum of 3.1.
Fleets are looking for that .5 to 1% fuel economy improvement with the same SAE grade.
Automotive approvals such as Dexos have fuel economy pass limits, and like FA-4s have low hths for grade as a result.
VMs or “VIIs” are not all bad especially when it comes to fuel economy, as they temporarily shear in the bearing clearance and reduce hths.
 
JamusMcFamus said:
Ok now that the Fun Police are done, anyone else?
Click to expand...
It has nothing to do with fun. The differences would be so small that you might need a sample size of 100K vehicles to see it. Use what you feel good about and get on with it. My son's 2016 Accord calls for 0w-20 but we run 5w-30 becuse multiple UOAs showed sub-par viscosity due to fuel dilution. Why not send a sample of your used oil off to the lab and then make some decisions based upon the analysis received?
 
yowps3 said:
Certainly not a 20% difference in fuel consumption between 2.9 to 3.5 HTHS oils
Click to expand...

True. Naming exact numbers is a bit hairy, but I'd try just to help
the OP:
I'd say a variation between 10 % in HTHS (e.g. 3.2 vs 3.5) would
probably result in roughly 1 % (or perhaps 2 %) difference in fuel
economy.
That explains what manufacturers actually do. Switching from a
5W-30 (HTHS 3.2-3.5) to a 0W-20 (HTHS ~2.7), so a difference in
20 % in viscosity incl. HTHS, makes 2 or 3 % improvement in fuel
economy (and CO2) with no expenses. Just the respective engine
should stand the lighter oil . . . .
.
 
I changed from the recommended 0W-20 to 5W-30 on a 5th generation Toyota 4Runner driven in Phoenix to have a higher HTHS. Given my annual mileage and MPG, a 1% loss in fuel efficiency equates to an extra 5 gallons of fuel consumed in a year. It's not worth my time and effort attempting to measure a change in MPG that small or even two times greater. It's only an extra $20/year in fuel cost.
 
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