Gas Gauge / MPG Problem

Drexler McStyles

Drexler McStyles

New member
I purchased a '97 Limited last month and really love it. It seems to be a well cared for, clean truck. The one issue I am having though is my MPG. We do mostly in town driving and as of the last tank, SEEM to be getting about 11 miles to the gallon. I have reset the EFI and changed the air filter. What I did notice though, when I last filled the tank, is that the gas gauge moves Reeeeaaaalllly slow from Empty to Full. Like it takes over an entire minute for the gauge to reach the top. Also, I waited until the gas gauge warning light came on last time before I refilled. Yet, the truck only took 15 gallons of gas. My understanding is that my truck has a 18.5 gallon tank. So, do i have a wacky gauge or bad MPG?
Does the fuel light come on because of a sensor in the tank, or because the fuel needle has reached a certain point?
 
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Hold up, first of all, how did you calculate MPG? I hope you're not dividing the miles driven by 18.5. Correct way is to divide the miles driven by the gallons filled (in this instance, 15 gallons).

Secondly, fuel gauge issue is pretty common in 3rd Gen 4Runners. You should see multiple threads regarding this using Google or search function. Not a big deal.
 
Dividing by 15 Im still only (supposedly) getting 13 MPG. Im thinking the only way to really know is to throw a gas can in the back and drive it until it runs out of gas. Then do the math.
 
No, you don't need to drive it until it is empty (highly unadviseable). The gas gauge does not come into play when calculating MPG. I hope you reset the trip odo when you last filled up. Drive for 2-300 miles, fill up, then divide the miles driven by the number of gallon you just filled up. Again, when you fill up doesn't matter. Do this several times to get your MPG.

Is the 4Runner stock? What size tires? 4WD, I'm assuming?
 
p nut said:
No, you don't need to drive it until it is empty (highly unadviseable). The gas gauge does not come into play when calculating MPG. I hope you reset the trip odo when you last filled up. Drive for 2-300 miles, fill up, then divide the miles driven by the number of gallon you just filled up. Again, when you fill up doesn't matter. Do this several times to get your MPG.

Is the 4Runner stock? What size tires? 4WD, I'm assuming?
Click to expand...

I used the trip odo for my calculation. Basically when the fuel light came on I had just gone over 200 miles. When I refilled it only took 15 gallons. So it sounds like Im getting 13 MPG, right? Yes, its 4wd. Pretty sure everything is stock.
 
Yes, that's correct. Were those 200 miles city or highway?

You may want to do a simple tune up, then go from there.
 
City miles have too many variables. How long did you sit and idle? How many "stop-n-go"? Average MPH? Etc. Even just filling up the gas tank has variables, as different pumps will stop pumping at different fill levels.

Better way is to measure highway miles, and get as many samples as possible.

But to answer your question, yes, it does seem low. You should be more like 16MPG.
 
Have you checked your tire pressure? I was getting about that when I purchased my 4Runner, improved quite a bit after matching the pressures recommended on the drivers door jamb.
 
Try this to calculate the MPG.

Fill the tank all the way up. You still can add about a 1 -2 gallons after pump stops. I some times pump all the way to the cap. You have to give some time for the trapped air bubbles to come out.

Zero the trip counter and drive....... and drive...

Stop at a gas station and refill all the way to the top and record the number of gallons pumped all the way to the second decimal place.

Now divide the miles in the trip counter by the number of gallons recorded above!
 
nissanh said:
Try this to calculate the MPG.

Fill the tank all the way up. You still can add about a 1 -2 gallons after pump stops. I some times pump all the way to the cap.
Click to expand...

I highly advise against doing this, as it may cause your Evap canister to fail.
 
i have a '99 4 CYL and get about 260 miles/tank city driving. I don't trust my fuel gauge after that though and rely solely on the odometer.
 
nissanh said:
Try this to calculate the MPG.

Fill the tank all the way up. You still can add about a 1 -2 gallons after pump stops. I some times pump all the way to the cap. You have to give some time for the trapped air bubbles to come out.

Zero the trip counter and drive....... and drive...

Stop at a gas station and refill all the way to the top and record the number of gallons pumped all the way to the second decimal place.

Now divide the miles in the trip counter by the number of gallons recorded above!
Click to expand...
Dont do this! Run the gas pump until it stops. Let it breathe for about 15 seconds, top it off, them stop. Filing, filling, filling is just going to kill your charcoal canister.
 
3.4l 96 has 265 75 16 stocks tires are 225 70 15 I get about 260 till the light mix driving as well I think u need a tune up
 
You do it once to calculate the MPG.

When I cross rural Nevada desert (Nevada US-50 "the loneliest road") I used to top it off just like that. I want to make it alive to the other end and I really didn't worry about the canister. So far truck runs fine without CEL all this time (CA truck with all the strict emission system)

Charcoal canister is activated carbon, and when it is saturated with petroleum vapor it will not absorb any more vapor. If you run 10 miles, that will create 1/2 gallon of space for the vapor to build up, and from there onwards the vapors in the canister will be sucked into the engine.
 
Last edited:
): calculate mpg by setting trip meter to 0 when full, and divided # gallons filled at next fill up by the # of miles on the trip meter = MPG

when my gas light comes on i only fill 13.5 gallons :0

i just drove to moreno valley from irvine ca (about 100 miles round trip with 2 other people.. going there was about 67-70.. on the way back i was 75-80) + 60 miles local

and im at half tank now.. from my estimation im about ~21

2000 limited, stock gearing, 2wd :l

time for a tuneup?
 
15 gallons is 55 liters. The tank is "supposed" to be 70 liters, but i rain it dead dry, and only filled up 65 liters before the nozzle clicked. I can (slowly) pump another 5 liters in if i want, but to be accurate with the scangauge, i always fill till it clicks (and try to use the same pump if available).
In reality your tank is 65 L (17 gallon) though you can force another 1.5 gallons into it.

That means when you filled up you had 10 liters of gas left in the tank (2.5 gallons).

BTW, your mileage is low.... even in the winter i get better than that city driving, check into your o2 sensors and do a full tune up / lubrication / oil change.
 
I'd start changing all common tune-up parts, fluids, filters, grease the driveshaft etc.
My wife gets 18.5 regularly - mixed hwy/city, but we've got a 5-speed. Just turned 192K.
 
I purchased my truck a couple months ago and was only seeing about 13-14 mph. (2002 4x4 sport, 3.4 on brand new 265x75x16's. 190k) The mileage was quite a disappointment so I went about doing the full tune up. Oil and filter, tranny fluid and filter, fuel filter, air filter, O2 sensors, pulled and cleaned the MAF and throttle body, diff fluid, transfer case fluid, greased the chassis, ran seafoam through my PCV line and put two cans through the gas tank, even bought the scangaugeII to try to monitor my driving. After all that I still don't get over 14. I can't figure it out to save my life.
 
nissanh said:
You do it once to calculate the MPG.

When I cross rural Nevada desert (Nevada US-50 "the loneliest road") I used to top it off just like that. I want to make it alive to the other end and I really didn't worry about the canister. So far truck runs fine without CEL all this time (CA truck with all the strict emission system)

Charcoal canister is activated carbon, and when it is saturated with petroleum vapor it will not absorb any more vapor. If you run 10 miles, that will create 1/2 gallon of space for the vapor to build up, and from there onwards the vapors in the canister will be sucked into the engine.
Click to expand...

Sure, in dire circumstances, why not? However, to suggest this method is ok on a normal basis, is absurd. Your original post did not specify doing it ONE time. Please be clear in your communication.

Secondly, even doing it one time *could* get you into trouble. You're talking about gas vapors being absorbed by the charcoal, which is correct. However, when the canister becomes SATURATED with liquid gasoline, it could cause problems. Mainly, the vents/piping could get clogged, preventing the gas tank to breath properly and tripping the CEL.

Will doing this cause permenant damage? No (other than maybe having to replace Evap system, worst case scenario). Is it worth it? Not to me. I mean, for what? More accuracy in calculating MPG? There are way too many variables for it to matter much in getting an accurate reading. Even doing it ONE time doesn't mean jack squat. You need multiple samples to work from. Instead of potentially shelling out $400+ for an Evap system, buy a $160 scangauge.

Lastly, if you're going to be out in the middle of nowhere? Carry an extra gas can.
 
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