Why is my MPG so low?

fiend busa

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You "shudder" at using brakes (60$) over wear and tear of you Downshifting and riding out gears to slow down? Hmm interesting

From 25mpg to 30mpg, thats a 15-20% difference in gas savings. Which is quite large mathematically speaking.
Rev match and yes - coasting in neutral is dangerous anyway (illegal in some countries), being in gear saved me from a few crashes when approaching a red light.

But to each there own - im just saying.





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pjw7454

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So I recently started tracking and manually calculating my mpg rather than basing it off the trip computer in the car. My most recent fill-up was 10.155 gallons at $3.47/gal. Car drove about 209 miles, and I filled up the car once the computer showed 25 miles remaining. Already sounds crazy without having to calculate the mpg. (basic math 209/10.155 = 20.6 mpg.) I'm not a terrible driver, I rarely go above 3k rpm and I go real easy on the gas and brake. I do drive city the majority of the time, like about 70% and 30% highway, but even then I shouldn't see my mpg this low, right? Everyone who has driven my car is always shocked about how quickly gas is used up despite not driving roughly.


Anyone know if this is normal, or if I should check something? I have a 2018 Civic EX. (2.0L)
I don’t believe that is normal. You should not be getting 209 miles on a full tank of gas in an 2018 model. You could have something seriously wrong with your car. Run it in eco mode always on to see if that improves it. Your ex has a turbo as well so it may be consuming gas faster but 209 miles is ridiculous. My 97 civic got 225 with a bad o2 sensor and cracked manifold. It’s possible your computer is jacked up and calculating less gas than what’s really there since it’s all digital. You should be under manufacture warranty so have them look at the gas tank sensor. It could be faulty. Mine says 300 on mine on full tank
 

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I don’t believe that is normal. You should not be getting 209 miles on a full tank of gas in an 2018 model. You could have something seriously wrong with your car. Run it in eco mode always on to see if that improves it. Your ex has a turbo as well so it may be consuming gas faster but 209 miles is ridiculous. My 97 civic got 225 with a bad o2 sensor and cracked manifold. It’s possible your computer is jacked up and calculating less gas than what’s really there since it’s all digital. You should be under manufacture warranty so have them look at the gas tank sensor. It could be faulty. Mine says 300 on mine on full tank
It's very possible to get less than 209 miles per tank. Very bad stop-and-go city driving is probably down around 15mpg average.
 
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JCH

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I don’t believe that is normal. You should not be getting 209 miles on a full tank of gas in an 2018 model. You could have something seriously wrong with your car. Run it in eco mode always on to see if that improves it. Your ex has a turbo as well so it may be consuming gas faster but 209 miles is ridiculous. My 97 civic got 225 with a bad o2 sensor and cracked manifold. It’s possible your computer is jacked up and calculating less gas than what’s really there since it’s all digital. You should be under manufacture warranty so have them look at the gas tank sensor. It could be faulty. Mine says 300 on mine on full tank
Thank you for your input! My EX is actually the non turbo 2.0L variant btw, I believe it was 2019 where they changed the EX to 1.5T. Anyways, to update y'all, I did take a freeway drive for 2 hours and got 32mpg (30mpg actually calculated). I'm just going to go ahead and guess that this is all normal and that city driving really does affect your mpg hardcore.
 

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Your mpg is very low. I drive my car pretty hard and in regards to being heavy on the throttle and i get 26-28ish mpg in the city with a small population of 75k, in the winter when it uses extra fuel to warm the car up. If I don't be heavy on the throttle i can easily get 30-33mpg in the winter. This is with the 2.0L. just a note to people saying about the turbo and fuel economy with spirited driving, both engines wind up using similar amounts of fuel regardless of the engine type, ive tested it myself. If the fuel economy is bad, it's probably a fueling issue. Have your dealer check the fuel trims, could be a bad MAF sensor or something
 

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Thank you for your input! My EX is actually the non turbo 2.0L variant btw, I believe it was 2019 where they changed the EX to 1.5T. Anyways, to update y'all, I did take a freeway drive for 2 hours and got 32mpg (30mpg actually calculated). I'm just going to go ahead and guess that this is all normal and that city driving really does affect your mpg hardcore.
To avoid future confusion, Canadian EX 2019 won't have the turbo, only the US version. We'll probably still need to specify later on.
 

Aurelleah

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I started driving s Si 2018 coming from a 2015 Lx (averaged 30mpg+). I was tripping the fuck out when i was getting 25mpg and trying to increase it... yes i drive streets to work not the highway. But i found 25mpg to be extraordinarily low compared to others.

1 tip is all it took...
Someone on here said stop using gears to downshift and slow down. Hold in the clutch or shift to neutral when you see a stop coming up. BOOOOM!

Instantly jumped my 2018 Si to 30mpg pn the streets. And when im driving "spirited" i get 28mpg now on the same streets to work.
This only applies if you spend a long time coasting in your commute as going to neutral stops engine braking. When you let off the gas in D and are coasting to a stop, the engine significantly cuts fuelling and just let's the engine pump air as a fuel saving feature. This is why you feel it coast more when going to neutral. But when in neutral it does cause the engine to use fuel, so it also only works when the gas you save on maintaining a speed is more than the gas when "idling". Keep in mind that in some circumstances it can be a safety risk to do this as you won't have power in the drive for an emergency if one comes up. Not terribly likely but something to keep in mind
 

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Rev match and yes - coasting in neutral is dangerous anyway (illegal in some countries), being in gear saved me from a few crashes when approaching a red light.

But to each there own - im just saying.
I almost never downshift if I'm coming to a stop. I'd rather replace rotors and pads than a clutch any day of the week. The only exception is if the weather is bad.

For the OP, I was going to ask if this was your first turbo car, but it appears you have the 2.0 N/T. Lots of people when they get their first turbo don't really understand how to drive it without boosting. Staying out of the boost when you don't need it is key to getting good MPG. I'm personally getting 43-45mpg combined, mostly expressway driving, on my 1.5T.

Does California screw with their gas like they screw with everything else? I know when we switch over to "winter blend" gas here in Michigan, I drop down to 38-39mpg. Maybe CA has a different gas?
 

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Make sure AC says 'off' if you don't don't need it. Remove excess weight from trunk and seats. Check engine air filter. Slow down accelerations. Check tire pressures! Try putting in at least 35psi per tire.

Reset the fuel gauge and watch what affects the mpg
 

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This only applies if you spend a long time coasting in your commute as going to neutral stops engine braking. When you let off the gas in D and are coasting to a stop, the engine significantly cuts fuelling and just let's the engine pump air as a fuel saving feature. This is why you feel it coast more when going to neutral. But when in neutral it does cause the engine to use fuel, so it also only works when the gas you save on maintaining a speed is more than the gas when "idling". Keep in mind that in some circumstances it can be a safety risk to do this as you won't have power in the drive for an emergency if one comes up. Not terribly likely but something to keep in mind


Ahhh shit, i see the confusion i have made. I think i forgot to mention im running a Standard transmission not a Automatic. My bad.
 

Aurelleah

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Ahhh shit, i see the confusion i have made. I think i forgot to mention im running a Standard transmission not a Automatic. My bad.
Sorry I said D but it applies to manual transmissions as well I'm pretty sure. If you watch your mpg meter in gear when coasting at high speed you'll probably see it approach infinity (or for Canadians it drops to 0L per hundred). If you go into neutral you'll see it climb a little bit to like 1-4L/hundred or something depending on your speed and the incline/grade of the road. I was basically mentioning that depending on your speed, you might not be saving much gas vs not going into neutral, because the engine cuts fuel when you take your foot off the accelerator. It's what makes engine braking in higher gears possible. In gear the momentum of the car in a straight drive is enough to keep the engine turning. In neutral it needs to start using fuel to keep the engine running since it has no other energy input if that makes more sense?

The long story short version is that coasting in neutral shouldn't make that much of a difference due to how the car saves fuel normally, however it does save decent amounts of fuel when you're going at highway speeds down any sort of slight incline
 

RobXsi

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Sorry I said D but it applies to manual transmissions as well I'm pretty sure. If you watch your mpg meter in gear when coasting at high speed you'll probably see it approach infinity (or for Canadians it drops to 0L per hundred). If you go into neutral you'll see it climb a little bit to like 1-4L/hundred or something depending on your speed and the incline/grade of the road. I was basically mentioning that depending on your speed, you might not be saving much gas vs not going into neutral, because the engine cuts fuel when you take your foot off the accelerator. It's what makes engine braking in higher gears possible. In gear the momentum of the car in a straight drive is enough to keep the engine turning. In neutral it needs to start using fuel to keep the engine running since it has no other energy input if that makes more sense?

The long story short version is that coasting in neutral shouldn't make that much of a difference due to how the car saves fuel normally, however it does save decent amounts of fuel when you're going at highway speeds down any sort of slight incline


Okay, i understand what your saying. But your not understanding what im saying. In my 18 Si, DOWNSHIFTING to a lower gear to slow fown for a stop or a red light will consume more gas due to high rpm spike of 4000rpm-6000rpms from down shifting. Via shifting into neutral for a stop or red light the rpms drop to 800rpm.

Does higher rpms consume more gas? And lower rpms consume less? Correct me if im wrong?
 

RobXsi

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Sorry I said D but it applies to manual transmissions as well I'm pretty sure. If you watch your mpg meter in gear when coasting at high speed you'll probably see it approach infinity (or for Canadians it drops to 0L per hundred). If you go into neutral you'll see it climb a little bit to like 1-4L/hundred or something depending on your speed and the incline/grade of the road. I was basically mentioning that depending on your speed, you might not be saving much gas vs not going into neutral, because the engine cuts fuel when you take your foot off the accelerator. It's what makes engine braking in higher gears possible. In gear the momentum of the car in a straight drive is enough to keep the engine turning. In neutral it needs to start using fuel to keep the engine running since it has no other energy input if that makes more sense?

The long story short version is that coasting in neutral shouldn't make that much of a difference due to how the car saves fuel normally, however it does save decent amounts of fuel when you're going at highway speeds down any sort of slight incline
And then, when im on the freeway im typically hovering 3000ish rpms. When i shift into neutral my rpms is 800rpms again. So im confused. Someone with science clarify this. Cause my MPG has increased by 15%-20% by doing what another poster recommended


Im NOt asking for variables of wind, humidity, tempature, weight of the vehicle, incline. What you ate for lunch that day.
 

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Okay, i understand what your saying. But your not understanding what im saying. In my 18 Si, DOWNSHIFTING to a lower gear to slow fown for a stop or a red light will consume more gas due to high rpm spike of 4000rpm-6000rpms from down shifting. Via shifting into neutral for a stop or red light the rpms drop to 800rpm.

Does higher rpms consume more gas? And lower rpms consume less? Correct me if im wrong?
Fuel economy is basically staying at a high load low rpm situation without lugging. The closer to 1500rpm you are, the better your fuel economy, due to pumping losses of higher rpm's if I remember correctly.

However, you'll probably notice that while engine braking causes your rpm to spike, your engine itself sounds much different than when you're at that rpm and also hitting the throttle. It sounds dry, like a quiet hum. That's cause it's not actually using fuel at those RPMs when you don't press the throttle, it's just pumping air. Part of why our cars are so good on gas compared to older cars is cause the ECU controls fueling like that.

Your mpg meter is probably gonna show different when engine braking but it's not actually using fuel like it says it is. Engineering explained has a good vid on it (and he drives stick too)
 
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So I thought I'd update this thread, I recently had my B1 service done and after that my MPG has increased.

Not sure what the real problem was behind it but I've been doing 50/50 freeway and city driving and am at 31.9mpg. I have not calculated the actual at the pump yet but the margin of error shouldn't be more than 1-2mpg. Yay!

E2E58CDF-2884-4689-B172-666D1BBF6CE7.jpeg
 

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