gas mileage

[chiefsfan1]

ok guys,
We got back from our trip to see her mom. I filled up and hit the freeway immediately.
No stops until we reached her mom at the care center. Computer said tank average was 37 MPG.
After several start and stops in town and the drive back home. no stops for gas until we got home. At the pump the computer said 34.6 MPG.
by hand the total mileage was 342.9 and put in 10.971 gallons. I get 31.2551272 MPG

Is the computer that wrong or just the way it calculates fuel burn?
This was in the Camry 2.5 I4

 

[JayhawkRoy]

My experience with the fuel estimator in a car is that is slightly optimistic vs real world calculation. This has been true for my F350 and our new Hyundai.

 

[spasm3]

Originally Posted By: JayhawkRoy
My experience with the fuel estimator in a car is that is slightly optimistic vs real world calculation. This has been true for my F350 and our new Hyundai.


My elantra is generous by about 2mpg on the computer.

 

[chiefsfan1]

Thank, I kind of wondered. This is my first car with all the toys on it.

 

[Jcp123]

Those factory FCDs are generally optimistic. How fast were you driving?

 

[chiefsfan1]

Originally Posted By: Jcp123
Those factory FCDs are generally optimistic. How fast were you driving?

I kept it at the speed limit. 70 MPH. Way too many cops on the route we were on......
The hiway was 4 lane and not flat. rolling hills, flat stretches etc.

 

[sicko]

Mine is always about 1 mpg higher than the actual calculated.

 

[fdcg27]

So a four cylinder Camry only delivers 31 mpg at only 70 mph in highway driving?
Our Accord will give 34 mpg under the same conditions if I keep speed down to seventy or so.
On a more serious note, the one car we have with fuel economy indication is our '09 Forester.
It tends to be about 10% optimistic, which is about what you saw with your Camry.
Kind of makes you wonder, since the car's computer has real-time data on fuel flow and road speed to work with.

 

[Eddie]

My Mazda CX5 on-board calculator agrees within ~0.5 MPG when doing most highway driving but, when checked locally it varies +/- 0.9 MPG. Sometimes hand calculation show less and sometimes more. I think the on-board calculator has a more difficult time with stop & go but, is surprising accurate on my Mazda. Ed

 

[datech]

My chevy Cobalt avg MPG has agreed with my calculated mpgs the few times I checked. The speedometer reads slow at highway speeds, though. It seems to be pretty close on the odometer miles.

What about the OPs odo reading, does it agree with the signposts along the highway? That could be a source of error just as the fuel burn could be wrong.

Don't worry, the gas stations NEVER sell you a short gallon, so that can't be the problem.

 

[hypervish]

My RX is usually within .5 mpg.

 

[Rand]

Possible combination you might have gotten more fuel in the tank than last fillup and its probably slightly optimistic.

hand calculated MPG is much more accurate averaging 3-4 fillups.


On a similar subject I put the factory yoko g91F pooptastic round and blacks back on (took off the blizzack ws-80)

Immediately broke 30mpg. Highest ever with ws-80's was 28.5mpg on an already warmed up return trip.

The yokos got 29.7 including 5mins of idle time. I expect to break 31-32 if I can manage to keep it around 65mpg highway as well. Its just as well they get great mpg because thats their only likeable feature besides fairly low noise.

dry traction is adequate, wet is below average but not dangerous, handling is.. average Hydroplaning is good(at nearly full tread depth I'd hope so) Snow traction is poor, Ice traction is non-existant.

We have 14+ days of above 40F weather coming so off with the blizzaks!

Also the trip mpg is easily within .5mpg of hand calculated so much that I trust it more than hand calculating with the inaccurate pumps here.

Obviously hand calculating 1000-2000miles of fill-ups makes the old miles/gallons more accurate.

 

[Jcp123]

Originally Posted By: chiefsfan1
Originally Posted By: Jcp123
Those factory FCDs are generally optimistic. How fast were you driving?

I kept it at the speed limit. 70 MPH. Way too many cops on the route we were on......
The hiway was 4 lane and not flat. rolling hills, flat stretches etc.


Rolling hills can kill if not approached the "right" way. Were you using cruise control? What kind of road surface (concrete/asphalt/chip seal)? Outside temperatures? Tire pressure?

I ask these more as rhetorical questions as fuel economy is a bit capricious. It rides on a lot of little things.

 

[chiefsfan1]

Originally Posted By: Jcp123
Originally Posted By: chiefsfan1
Originally Posted By: Jcp123
Those factory FCDs are generally optimistic. How fast were you driving?

I kept it at the speed limit. 70 MPH. Way too many cops on the route we were on......
The hiway was 4 lane and not flat. rolling hills, flat stretches etc.


Rolling hills can kill if not approached the "right" way. Were you using cruise control? What kind of road surface (concrete/asphalt/chip seal)? Outside temperatures? Tire pressure?

I ask these more as rhetorical questions as fuel economy is a bit capricious. It rides on a lot of little things.


yes, cruise was on the whole time. Plus I have new tires on it. Road surface was varied, concrete to asphalt then back again.
I need to check the odometer to see how close it actually is.

 

[rjundi]

The manual method assumes the pump shuts off at the same exact point every time at shutoff. For whatever reason I believe the shutoff mechanism works off pressure which can vary and other variables?

Also shutoff is controlled by gasoline pump(correct?) which introduces a variance pump to pump. The smaller the fuel tank or fillup the greater the variance in MPG computer vs manual method.

 

[Joel_MD]

For two of my vehicles I have tracked every gallon of fuel purchased plus odometer readings on an Excel spreadsheet so I can keep track of fuel economy. For both vehicles the fuel economy shown on the car's computer tends to be about 2 MPG higher than actual.

 

[Benzadmiral]

The dash readout on my '03 Park Avenue was always about 10% higher than calculated. That on the Regal varies. It's always high, but sometimes half an mpg higher (21.5 on the DIC, 21 calculated) and sometimes 1.5 higher. Rarely is it 10% too high, though.

 

[Mykl]

My GTI's fuel monitor is reasonably accurate up to about 31 mpg. Up to that, at most it's 1.5 mpg off, but usually less than 1 off.

After that it gets a little screwy. I've made it read as high as a sustained 45 mpg (funeral procession at 40-45 mph for an hour). But any time it reads, on average, anything exceeding 35 mpg it's guaranteed to be off by at least 4, usually more.

The best I've managed to get out of the car was about 35 mpg sustained over a single tank, but I don't recall what the display read.

 

[SHOZ]

On my Genesis Coupe mine was way off until I got some tires that were bigger and it corrected the fast speedometer error. Funny though as the odometer is even more off in a slower direction.

 

[SteveSRT8]

Originally Posted By: SHOZ
On my Genesis Coupe mine was way off until I got some tires that were bigger and it corrected the fast speedometer error. Funny though as the odometer is even more off in a slower direction.



I am surprised that your tuner does not allow you to program in different tire sizes. Might want to check with the supplier and see if they can offer that to you. Diablosport does on many different platforms, but I realize that may not work with Hyundai/Kia...