Difference in MPG using different oil viscosities?

[SubieRubyRoo]

I find that probably a hair high. I went from 0/5w20 to 0w40 in my Odyssey, and saw less than a 0.3mpg (mid-26s on both) difference that was more dependent on season than oil grade.

Depending on ambient temps, there may be some differences, but the thicker oil will run a little hotter and therefore be a little thinner than at the temps your thinner oil ran at. Wish you still had the chart; @dnewton3 is a master statistician and could have deciphered it if you had ambient temp data and a bunch of the other variables besides grade in the chart.

 

[kschachn]

I seem to get between 0.25-0.40 MPG less using a 5w-40 vs a 5w-30 but there were some variables that took place so not for certain. Let's say I get 0.25 miles per gallon less, 20 MPG, & $2.50 gallon average. Over 100k miles that would be $3,125 more dollars.

That’s utterly fantastic. How do you accomplish this? Which standardized test fuel are you using?

 

[stormgol]

get the highest quality, lowest rolling resistance tires you can get if you want to save on fuel. and get lighter wheels. highest gains will be with smaller, lighter wheels with low rolling resistance tires. if you really want to save on fuel, change your driving habits. adopt driving habits that favor low fuel consumption. avoid hard acceleration, avoid hard braking, avoid high rpm's and reduce your speed. CAFE is a bureaucrat joke.

 

[I<3oil]

Have used 0W-20 and also 5W-30 in the CRV and Odyssey....never been able to tell a discernible increase or decrease.

 

[xmanjeff]

my best fuel efficiency was always just before i needed an oil change , chevy 1.5 turbo

 

[PandaBear]

I remember some research quoted number the oil industry published saying it will be up to 1.5% and more likely 0.5-1% between 5w20 and 5w30. It is probably very hard for human to observe it in a non controlled environment.

 

[kschachn]

I remember some research quoted number the oil industry published saying it will be up to 1.5% and more likely 0.5-1% between 5w20 and 5w30. It is probably very hard for human to observe it in a non controlled environment.

Yes, with other uncontrollable variables that have equal or greater significance it makes it impossible.

I once linked an article here that discussed measuring real-world fuel economy and how difficult that was. The article noted that one absolute need was to use standardized test fuel with a consistent BTU content. Without that it was impossible to get any sort of repeatable measurement. They noted that even at the same gas station fuel varied about 4% in energy density. And this was irrespective of seasonal variations which were larger.

 

[Nessism1]

Without controlled testing, it's impossible to definitively say how much viscosity affects mpg. Clearly, it does, though, or all the car manufacturers wouldn't be specing the thin oils they do.

What I know, regarding my Civic, is that I CAN notice a difference in the way the engine responds to throttle, particularly when cold, between 0W-20 and 5W-30. Non-scientific opinion, mine, but I stand by it. The engine revs easier with the thinner oil. It's a smig quieter with the thicker oil.

 

[Patman]

One of the problems in the real world with nailing down small changes in fuel economy is that wind and wet roads play a factor. I do notice a big difference in my average between the cold weather and the warm weather, and I definitely see a huge difference between the winter blend and summer blend. But I know that I would have an impossible task with seeing a difference between a 0w20 and a 0w30.

That being said, since I drive my Civic very gently and I put 20-25k a year on it, I want to save money on gas (which is expensive up here!) so I’m sticking with 0w20. Even if it’s only worth 1/2% improvement, it’s still worth it to me in the long run.

 

[D1dad]

I can always tell the exact moment when I’m getting the summer blend of gas because it’s worth an honest to goodness 10% improvement in my Civic!

Yep. Winter blend is a killer for sure.

 

[Rand]

One of the problems in the real world with nailing down small changes in fuel economy is that wind and wet roads play a factor. I do notice a big difference in my average between the cold weather and the warm weather, and I definitely see a huge difference between the winter blend and summer blend. But I know that I would have an impossible task with seeing a difference between a 0w20 and a 0w30.

That being said, since I drive my Civic very gently and I put 20-25k a year on it, I want to save money on gas (which is expensive up here!) so I’m sticking with 0w20. Even if it’s only worth 1/2% improvement, it’s still worth it to me in the long run.

what tires are you using? the right tires could get you 10x that improvement.

 

[Patman]

what tires are you using? the right tires could get you 10x that improvement.

I have Nokian WRG5s. I need all weather tires so I can’t really run those very low resistance tires that might get me better MPG

 

[y_p_w]

Gas mileage will depend on gas quality way more than oil viscosity.

I wouldn't say "quality" because for the most part base fuel is base fuel. Additives are another matter in terms of long term performance, but that usually won't result in immediate differences like base fuel will.

The primary driver for fuel economy (all other things being equal such as octane rating, motor oil, etc.) is energy content. And there's a wide range of energy content based on factors that the refiner may find hard to control, such as crude oil source.

This mentions a "Gasoline Gallon Equivalent" which is about a standard energy content for a gallon of gasoline. This says that a gallon of gasoline can have anywhere from 97-100% of a GGE. It also mentions that 1 GGE is equivalent to [correction] 0.88 Diesel Gallon Equivalent, since diesel is inherently more energy (and mass) dense than gasoline.

https://afdc.energy.gov/fuels/properties​

Gasoline/E10​

​

Energy Comparison [2]​	1 gallon of gasoline has 97%–100% of the energy in 1 GGE. Standard fuel is 90% gasoline, 10% ethanol.​

As far as I know, there's no way to specify what you get other than meeting a spec. The industry only deals in volume and all commodity fuel is treated the same if it meets a certain standand. The same refinery can have energy content go up and down for a particular spec. Fuel goes through pipelines and they can be mixed from different sources. That's just the way the industry works, even though fuel marketers have a lot of people convinced that fuel is different (other than their additive package).

 

[KevinMalone]

You would assume it would make a difference based on how manufacturers continue to specify thinner and thinner oils

 

[fantastic]

I seem to get between 0.25-0.40 MPG less using a 5w-40 vs a 5w-30 but there were some variables that took place so not for certain. Let's say I get 0.25 miles per gallon less, 20 MPG, & $2.50 gallon average. Over 100k miles that would be $3,125 more dollars.

UPDATE: I looked at my notes & this is what I saved recently. 0.30 MPG less from 30 to 40 grade BUT 40 had more weight, idling, etc on the 40. That is a spec less than 1.5% less MPG going from 5w-30 to a 5w-40 Euro oil. It would cost slightly more over 100k miles as I quoted above for fuel cost increase.

Using 5w-30 XC90 returned 20.5 MPG over 4,729 miles
Using 5w-40 XC90 returned 20.2 MPG over 4,855 miles (more weight w/kids, winter idling, viscosity)

 

[kschachn]

UPDATE: I looked at my notes & this is what I saved recently. 0.30 MPG less from 30 to 40 grade BUT 40 had more weight, idling, etc on the 40. That is a spec less than 1.5% less MPG going from 5w-30 to a 5w-40 Euro oil. It would cost slightly more over 100k miles as I quoted above for fuel cost increase.

Using 5w-30 XC90 returned 20.5 MPG over 4,729 miles
Using 5w-40 XC90 returned 20.2 MPG over 4,855 miles (more weight w/kids, winter idling, viscosity)

How much of what you observed is due to the oil?

 

[PWMDMD]

I've used 0W20, 5W30 and 0W40 in all my vehicles and while I'm sure there is some small difference, it's not enough to notice or care.

 

[fantastic]

I've used 0W20, 5W30 and 0W40 in all my vehicles and while I'm sure there is some small difference, it's not enough to notice or care.

Right, The biggest difference in MPG decrease that I quoted above was mostly from winter idling. That has the biggest impact rather than a higher viscosity from my experience.