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Ask HN: Is your ICE car getting less MPG lately?

12 points by tamaharbor 5y ago

Ever since the cost of gasoline has skyrocketed, my Toyota has gone from ~30 to ~23 miles per gallon. Engine running fine, spark plugs and air filter are good. Have you experienced this also?

h2odragon 5y ago
Ask your Dept of Weights and Measures to test the gas. You may be getting more ethanol than you expect
CarVac 5y ago
I've gotten the same 50 mpg in my 04 Prius.
samwillis 5y ago
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?
- unfocussed_mike 5y ago
  If they are in the UK, the optimal strategy for dealing with a car that can only do 23MPG will soon be to rip out the entertainment system, take the tires and abandon the car by the roadside. It could be costing the equivalent of $1/mile for fuel alone within a couple of months.
  - lesserknowndan 5y ago
    If they were in the UK wouldn’t they say miles per litre? Asking because I’m curious…
    - corobo 5y ago
      The UK’s secret shame is that we use metric in front of Americans but then we go right back to using miles per gallon, miles in general, stones to weigh ourselves, pints for alcoholic drinks, litres for non It’s a total mess
      - unfocussed_mike 5y ago
        Fahrenheit when it's hot, celsius when it's cold...
        deleted 5y ago
        [deleted]
    - unfocussed_mike 5y ago
      No, as corobo says below, we never _say_ miles-per-litre; not even really young people who have only known litres at the pump.
      - pvorb 5y ago
        How about kilometers per litre?
        p49k 5y ago
        In most of Europe it’s not km/l but instead l/100km (number of liters required to drive 100km). It’s IMO a better way to frame consumption of resources.
        ProblemFactory 5y ago
        I think we could reduce the litres / km (volume / distance) units to just square meters (area). For example, 7 litres / 100km = 0.07 mm^2 It's the cross-section of a noodle of fuel laid out along the road that the car needs without a gas tank.
  - hakfoo 5y ago
    Don't forget to rip out the catalytic converter.
- giantg2 5y ago
  I agree that the energy difference is small, although it's possible that the mpg could be affected more than that depending on if the engine was designed to utilize that energy efficiently (different burn rates and engine characteristics like bore/stroke/compression/timing can produce different results).
garyfirestorm 5y ago
Sometimes the ECU takes a while to adapt to new fuel.
TheJoeMan 5y ago
Well my BMW, which I admit doesn't have the greatest MPG, has gone from 20 city to 16 city MPG.
- HstryrsrBttn 5y ago
gregors 5y ago
I like the https://www.fuelly.com 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 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.
dm319 5y ago
Apart from the E10 issue, they may have started leaving out fuel additives to lessen the increasing costs.
shakezula 5y ago
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.
culopatin 5y ago
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.
giantg2 5y ago
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
jmrm 5y ago
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.
JeremyBanks 5y ago
tonyarkles 5y ago
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.
- doubled112 5y ago
  I'm sure there are many reasons, but I expect worse fuel economy in the winter. Winter tires are less efficient. Winter diesel is supposedly less efficient - gasoline I believe also changes formulas in the winter in some places. Does a warm car run more efficiently than a cold car? I think so, and mine takes many minutes to get up to operating temperature. On a short trip, I may never get there.
m3047 5y ago
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.
saltcured 5y ago
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.
rs999gti 5y ago
Maybe you are still on winter blend? https://www.bellperformance.com/blog/bid/49483/fuel-mileage-dropping-blame-the-winter-blend-gasoline#:~:text=In%20terms%20of%20gas%20mileage,you%20used%20in%20the%20summer https://www.bellperformance.com/blog/bid/49483/fuel-mileage-....
dlsa 5y ago
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.

12 points by tamaharbor 5y ago

Ever since the cost of gasoline has skyrocketed, my Toyota has gone from ~30 to ~23 miles per gallon. Engine running fine, spark plugs and air filter are good. Have you experienced this also?

h2odragon 5y ago

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

CarVac 5y ago

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

samwillis 5y ago

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?

unfocussed_mike 5y ago
If they are in the UK, the optimal strategy for dealing with a car that can only do 23MPG will soon be to rip out the entertainment system, take the tires and abandon the car by the roadside. It could be costing the equivalent of $1/mile for fuel alone within a couple of months.
- lesserknowndan 5y ago
  If they were in the UK wouldn’t they say miles per litre? Asking because I’m curious…
  - corobo 5y ago
    The UK’s secret shame is that we use metric in front of Americans but then we go right back to using miles per gallon, miles in general, stones to weigh ourselves, pints for alcoholic drinks, litres for non It’s a total mess
    - unfocussed_mike 5y ago
      Fahrenheit when it's hot, celsius when it's cold...
      - deleted 5y ago
        [deleted]
  - unfocussed_mike 5y ago
    No, as corobo says below, we never _say_ miles-per-litre; not even really young people who have only known litres at the pump.
    - pvorb 5y ago
      How about kilometers per litre?
      - p49k 5y ago
        In most of Europe it’s not km/l but instead l/100km (number of liters required to drive 100km). It’s IMO a better way to frame consumption of resources.
        ProblemFactory 5y ago
        I think we could reduce the litres / km (volume / distance) units to just square meters (area). For example, 7 litres / 100km = 0.07 mm^2 It's the cross-section of a noodle of fuel laid out along the road that the car needs without a gas tank.
- hakfoo 5y ago
  Don't forget to rip out the catalytic converter.
giantg2 5y ago
I agree that the energy difference is small, although it's possible that the mpg could be affected more than that depending on if the engine was designed to utilize that energy efficiently (different burn rates and engine characteristics like bore/stroke/compression/timing can produce different results).

garyfirestorm 5y ago

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

TheJoeMan 5y ago

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

HstryrsrBttn 5y ago

gregors 5y ago

I like the https://www.fuelly.com 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 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.

dm319 5y ago

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

shakezula 5y ago

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.

culopatin 5y ago

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.

giantg2 5y ago

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

jmrm 5y ago

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.

JeremyBanks 5y ago

tonyarkles 5y ago

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.

doubled112 5y ago
I'm sure there are many reasons, but I expect worse fuel economy in the winter. Winter tires are less efficient. Winter diesel is supposedly less efficient - gasoline I believe also changes formulas in the winter in some places. Does a warm car run more efficiently than a cold car? I think so, and mine takes many minutes to get up to operating temperature. On a short trip, I may never get there.

m3047 5y ago

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.

saltcured 5y ago

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.

rs999gti 5y ago

Maybe you are still on winter blend? https://www.bellperformance.com/blog/bid/49483/fuel-mileage-dropping-blame-the-winter-blend-gasoline#:~:text=In%20terms%20of%20gas%20mileage,you%20used%20in%20the%20summer https://www.bellperformance.com/blog/bid/49483/fuel-mileage-....

dlsa 5y ago

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.