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How accurate are in-car MPG computers?

yh125d

yh125d

Diamond Member
I'm not in the habit of keeping receipts so I can't really check against mine

If it is accurate, I'm very disappointed with Ford and how they geared the 5sp in my Fusion. Over the first 2600 miles(month) I apparently averaged only 26.7 mpg with it running so high, and thats 90% highway (half and half 70mph vs 82 or so). I may have to accelerate my plan to sell this when the miles get too high and buy a TDI. With putting 35k+ miles a year on, I can't afford this MPG!

If accurate, that means I'm spending ~215 a month just on gas. That's another car payment. And this is the part of the year I don't drive very much...

I'm lucky gas is so cheap here. Only ~$2.30 for 87, ~2.50-2.60 for diesel
 
How about you fill the tank full.

Drive around till you get 200miles in the tank

refill the tank.. figure out the gals you put in and then divide it by 200miles.

Otherwise my Acura TL's computer seems to come within 1-2MPG's of actual.
 
Typically they aren't very accurate. On my car, it says I average 25.5 MPG but calculating every fill-up, it is more like 24. I've also got a real-time MPG monitor and when coasting, my MPG goes to infinity... which is obviously impossible.

So, most likely, you are getting worse MPG than what your car is telling you.
 
I know how its done :|


I just can't make myself make it a habit for long enough to get an accurate result. 200 miles is less than 2 days for me, I'd want to go a full week or two to get an accurate number with weekends included
 
yh125d said:
I know how its done :|


I just can't make myself make it a habit for long enough to get an accurate result. 200 miles is less than 2 days for me, I'd want to go a full week or two to get an accurate number with weekends included
Click to expand...

But with those 200 miles you can check the accuracy of the digital gauge (reset it before you drive the 200 miles). You don't have to keep doing it.
 
lolol. I was looking through my fathers average mpg on his SRT8 300, and it said 8.2MPG...lol

He has a lead foot though.
 
If 215 a month is going to break you, you need to sell your current car and buy a $500 beater piece of shit to drive around so you don't have a car payment.

My truck gets the best MPG out of the vehicles I drive. And it only gets 17MPG.
 
KIAman said:
Typically they aren't very accurate. On my car, it says I average 25.5 MPG but calculating every fill-up, it is more like 24. I've also got a real-time MPG monitor and when coasting, my MPG goes to infinity... which is obviously impossible.

So, most likely, you are getting worse MPG than what your car is telling you.
Click to expand...


your mpg is infinite if you are coasting and in gear. the momentum of your car is turning the engine. the fuel injectors are shut off.

edit: also, my scangauge is usually within 1 mpg. different pumps fill to different amounts too, so there is some error from that as well
 
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yh125d said:
I'm not in the habit of keeping receipts so I can't really check against mine

If it is accurate, I'm very disappointed with Ford and how they geared the 5sp in my Fusion. Over the first 2600 miles(month) I apparently averaged only 26.7 mpg with it running so high, and thats 90% highway (half and half 70mph vs 82 or so). I may have to accelerate my plan to sell this when the miles get too high and buy a TDI. With putting 35k+ miles a year on, I can't afford this MPG!
Click to expand...

Well, driving at 80+ mph sure as hell isn't helping you out. 😛

I don't recall Fusions being geared badly when I was renting them, and I usually managed about 27 mpg in mixed driving (about the same as your mix) with 32-34 mpg on the freeway. Yours doesn't seem to be far off that at all. Even a tiny bit of city driving will drag fuel mileage down.

ZV
 
Zenmervolt said:
Well, driving at 80+ mph sure as hell isn't helping you out. 😛

I don't recall Fusions being geared badly when I was renting them, and I usually managed about 27 mpg in mixed driving (about the same as your mix) with 32-34 mpg on the freeway. Yours doesn't seem to be far off that at all. Even a tiny bit of city driving will drag fuel mileage down.

ZV
Click to expand...

No kidding!
 
Zenmervolt said:
Well, driving at 80+ mph sure as hell isn't helping you out. 😛

I don't recall Fusions being geared badly when I was renting them, and I usually managed about 27 mpg in mixed driving (about the same as your mix) with 32-34 mpg on the freeway. Yours doesn't seem to be far off that at all. Even a tiny bit of city driving will drag fuel mileage down.

ZV
Click to expand...

80mph Is a perfectly normal speed on the interstate 😛


And the autos are much better, but the 1G 5 speed has a different 5th which raises RPM considerably on the interstate, to a level more suited to a car with a 1.6l 4 instead of a 2.3...

But according to my trip computer I get only 27-28ish on the interstate. Slightly better on 2 lane highways at 70, and pretty good in town.


I do have a pretty hilly commute, which I know does not help at all, but even on flat interstate it seems under 30
 
You should have bought a corolla
cheaper car and better mileage but 80 and hills?
you're asking a lot of any car esp of a midsize
 
I average more than that with my AWD 2010 Outback.

Anyway, the MPG computer in my car is usually ~1 mpg too high.
 
Zenmervolt said:
Well, driving at 80+ mph sure as hell isn't helping you out. 😛

I don't recall Fusions being geared badly when I was renting them, and I usually managed about 27 mpg in mixed driving (about the same as your mix) with 32-34 mpg on the freeway. Yours doesn't seem to be far off that at all. Even a tiny bit of city driving will drag fuel mileage down.

ZV
Click to expand...

Interesting, I get 30MPG @ solid 80MPH (130KM/H)

Summer a little better 32MPG
 
Mine is fairly accurate. It displays 25 MPG highway, and I used 16 gallons on a 400 mile trip. As for city, it's getting there slowly, a couple thousand miles of highway cruising is keeping it a little on the high side.
 
My 04 Suburban is generally dead on. We took a trip up to see the wife's family, and had to fill up before we got there. (long trip) When I filled it up, the trip computer said I had used xxx gallons...and that's exactly what it took to fill it with. Got a bit over 18mpg for the trip, which also worked out when doing the math manually.
 
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