Oil weight observation and fuel economy

More viscous oil = more hydrodynamic friction = more power/efficiency loss

A 1 mpg difference from a single data point isn't conclusive of anything to me though. That could be the difference between winter and summer fuel blends.
 
My experience: changed from 0w20 to 5w40.

Zero difference in MPG. I posted such a couple years ago. Accumulated 100k miles in under 36 months. Same drives, same speeds, same fuel.
 
I’m guessing the mileage calculator was ran for a much longer time when the engine was filled with 5w30 with more highway miles in the mix. 🤷‍♂️
 
I've only had a couple of cars with fuel consumption on the dash, acuracy is near enough, and something to keep you entertained. With my Volvo nothing at all made a difference to fuel economy except the right foot. Oils from 5W-30 to 15W-60, AC, weather, tyre pressures, showed no difference in fuel economy. On a quiet night on the motorway with no traffic it would show some impressive figures, towing a loaded trailer would use twice the fuel...get it on boost and it would suck fuel.

Now I have a Honda Airwave (Honda Fit stationwagon) and everything effects fuel economy - AC, tyre pressures, weather, it all shows on the gauge. I've just topped up the oil with 500ml of 15W-40, and fuel economy has dropped considerably. The design focus of this car is all about fuel economy, and it shows.

I'm fighting it, but I might have to convert to the Thin Side...
 
I’m guessing the mileage calculator was ran for a much longer time when the engine was filled with 5w30 with more highway miles in the mix. 🤷‍♂️
The current calculation is based on the last 2900 miles with roughly 900 being with the new oil.
 
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years ago when deciding on which Full synthetic oil to use, I tried similar grade Mobil, shell & castrol. Mobil gave me 5% better mpg (and close to 10% compared to original non synthetic)

Also I have noticed looking at data sheets, that as an example, 5w30 has a lower cold temp viscocity than a 5w40 which could impact the mpg and that in general the viscocity for the same grade is different from one brand to another
 
years ago when deciding on which Full synthetic oil to use, I tried similar grade Mobil, shell & castrol. Mobil gave me 5% better mpg (and close to 10% compared to original non synthetic)

Also I have noticed looking at data sheets, that as an example, 5w30 has a lower cold temp viscocity than a 5w40 which could impact the mpg and that in general the viscocity for the same grade is different from one brand to another
Wow that’s really something. Did you ever tell Mobil about this?
 
No I didn't including that the engine was trouble free and sweetly for over 200k miles before the car was stolen!

We are talking about the 90's. Now the difference is probably a lot less
 
Didn't US Gov mandate going from 10% to 15% alcohol in all gas just recently? I get worse gas mileage after I fill up in USA vs Canada lately as well.
 
Didn't US Gov mandate going from 10% to 15% alcohol in all gas just recently? I get worse gas mileage after I fill up in USA vs Canada lately as well.
Hardly a mandate to put E15 in all gasoline. Google hits all over the place.


"Only 2,300 US gas stations—about 1.5% of the country’s roughly 150,000 fueling stations—sell E15 gas. The remaining 98.5% of gas stations may not have the proper equipment (pdf) to safely store E15."
 
in-your-head-dolores-oriordan.gif
 
You're not imagining things.
The vehicle's dash. Nothing hand calculated. Just found it interesting it stayed the same as long as I had 5w-30 then changed once 5w-40 was introduced. I'm pretty sure it will trend down further before it settles based on the trip averages I have seen.
Yeah this can be a thing depending on the oil. I ran the factory Castrol Syntec/Euro 5w40 and sometimes 0w40 on all my VWs forever and then suddenly switched to PPE (just for fun/variety) and noticed an immediate! 2-3mpg drop using the dash computer on the same road at the same temperatures at the same cruise speed. Pissed me off so bad I dumped the oil after 1k and put back in the Castrol. Immediately regained my mileage. People will try to tell you this is not true. I pay ultra close attention and I can tell you. It does matter. Choose what you like best I guess.
 
I wonder if the torque of an engine has an effect on how much viscosity affects mileage. More torque, or the engine spending more time in its peak torque rpm range, may reduce the effects of a higher viscosity oil on mpg? Just thinking out loud.
 
There is so much variation in one's gas mileage without changing the weight of oil that it's hard to detect what the change in gas mileage would be with a different oil short of a formal lab measurement. However, I did a different test 10 years ago. I plotted the octane level with gas mileage. One good thing was my driving patterns were very stable, the weather was roughly the same with no cold spells (Miami), my car was used for longer distances so it was warmed up. For nearly a year, I plotted mpg versus octane. I varied the octane and calculated the octane in my tank, such as 90.2 or 92.8, etc.

I found a slope with some noise in the data. I also found that the EPA tested my car with regular and with premium and published a 1 mph difference, which corresponded with my data, which was a little more limited, ranging from 89.8 octane to 93, not 87.

(Oh, a different topic. Does the moderator sometimes close a thread and delete recent posts because they are essential repetitive / similar info?)
 
I went from 5w20 to 15w40 in the Crown Vic and saw zero change in MPG I haven’t hand calculated it but it avgs 21mpg which is roughly 4 trips to work and since I’ve went up in viscosity I still get 4 trips to work so
 
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