Is your ICE car getting less MPG lately?

No. Same mpg in all three. 2 use premium, one regular (GLI, turbo Miata, Prius) There is something wrong with your car you just haven’t seen it yet. I’d get an odb2 scanner and look at real-time data. Duty cycle and o2 readings in particular.

Extrapolating your sample of 1 to the population mpg and assuming a correlation with the fuel price change is as relevant as making a correlation with the horoscope predictions of the month. There are so many things that could change that reading that you’re not telling us that this post is pretty useless.

It would be more useful to try to troubleshoot your mpg change.

Are you in the UK or somewhere that has just swapped to the new E10 formula for Unleaded Petrol (10% Ethanol, the old was 5%)?

I have heard various anecdotal stories of people seeing a drop in MPG, although I would only expect it to be about 3-5% as that’s how much less energy there is in the fuel.

Some older cars aren’t fully compatible with E10, maybe that could be the problem?

If you know a lot of people who share the same experience with you, it might be something fishy, but if it doesn't, it might be time to check your car.

How dirty are the injectors, how clean are the air filter, how good are the spark plugs, if the mass air flow sensor works OK, and some other parts that could make your car to use more gas. All of this can be inspected by any good mechanic easily.

I like the https://www.fuelly.com web site to see what other people are getting as well as trend lines. For example - https://www.fuelly.com/car/toyota/prius/2021

In my area there are 2 types of gas stations - ones with Ethanol and ones that target motorcycle advertising "100% gas" which is more expensive, but you definitely get more MPG. If I were you I'd try a different brand for a few fill ups and chart the differences.

I have a 30 year old (how did that happen!?) motorcycle. It's not a "sport" bike (UJC with good ergos) but it does have a high (10.5:1) compression engine (drive train is borrowed from a different bike by the same manufacturer, lower compression). (They should have upgraded some other things, like the clutch springs; we've all had to shim them at some point.)

I remember when ethanol fuel came out.

* I no longer needed to run premium in it unless it was really hot outside, plus was fine.

* I actually get better highway mileage with the ethanol fuel.

* It warms up better / faster when it's cold if I run regular.

There are myriad reasons that mileage could decrease. I haven’t experienced this recently, but I have had random decreases in mileage before.

Someone else in this thread mentioned having the gas tested and that could be possible but i would consider it unlikely.

If you’ve checked spark and air filters, my next questions would be transmission and tires. Are your tires at the proper air pressure? Is your transmission slipping at all? Are your plugs fouled at all?

You could ask a dealership to run a diagnostic, Toyota’s dealership technicians are actually pretty good.

Ask your Dept of Weights and Measures to test the gas. You may be getting more ethanol than you expect

Maybe you are still on winter blend?

https://www.bellperformance.com/blog/bid/49483/fuel-mileage-....

No.

But while I'm thinking of it, has anyone had any issues leaving a wifi or bluetooth obd2 gadget plugged in all the time? I'm thinking of doing a thing with the nearest bored raspi I find but I'll need continuous obd2 sourced data.

Think in terms of recording / graphing etc.

What time frame are you talking about? Have your driving habits changed in the same period? The kind of difference you are describing is what I would see between longer cruising trips versus lots of short trips where the car barely warms up.

Mine has been worse for the last 6 months, but that happens every winter. Now that daytime temperatures are positive instead of negative, I expect it’ll improve again soon.

Nope. I was surprised at how high my mileage has been when I recently hauled 1200 lbs of fencing and got 20.5 mpg for that trip

Apart from the E10 issue, they may have started leaving out fuel additives to lessen the increasing costs.

Well my BMW, which I admit doesn't have the greatest MPG, has gone from 20 city to 16 city MPG.

Sometimes the ECU takes a while to adapt to new fuel.

I've gotten the same 50 mpg in my 04 Prius.