Mystery Gas Mileage

[odeek9]

I'm perplexed This may not be considered a problem but something must be wrong. !986 Ranger I've had for 27 years. 2.3L, EFI, gas, 5 speed. Rebuilt engine 3 years ago and only has about 15,000 miles on it. Runs great though it idles just a tad roughly. I believe it needs to be timed but I'm too old now to do such things. Did a compression test (am OCD about it) a month ago with all 4 cylinders ranging from 185-190 psi.
My question: I normally get around 21 mph-live in the woods and 90% of my driving is to town and back on one lane roads for about 10 mi. roundtrip. On the freeway maybe once a month. 2 tank fills ago my MPG had risen to 26. Last fill up it was back to 22. Today it was 31!! I use my odometer for mileage checks as the gas tank gauge gets erratic when 1/2 full and less. So it's not that and it's not my math-today odometer read 159 (I usually fill up before 175 as I can't run out up here) and it took 5.1 gallons. Any thoughts would be appreciated, alan

 

[NebrRex]

Maybe your getting something a little different out of the pump.

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[odeek9]

Maybe your getting something a little different out of the pump.

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I guess that I'm being slow but I don't follow. I only use Chevron as it's my only card-brother's actually as he pays for my gas

 

[NebrRex]

The formulation of the gas could be a little different from one batch to another.
That would result in the fuel burning differently from one tank to another. Or the
work load of the engine changed. What do you mean by 'timed'?

.

 

[odeek9]

That would make some sense except for the fact that its never happened until very recently and an 8 mpg difference is huge in my estimation. But it's as good a guess as any so far.
Ignition timing with my light. It was never-or I'm assuming that's what it is-exactly right after they put the Jasper engine in. I mentioned it to the mechanic and he said that per his info it was spot on but he still made a minor adjustment. What he did I'm not quite sure. I'd time it, though it's been 20 years since I've done it (had to do it, seemingly, every month with my Triumph Spitfire) but I can't even see the bolt, or whatever, that holds the distributor in place. I know where it's suppose to be but I can't locate it and when you only have one vehicle in the middle of nowhere, relatively, it's not always wise to get involved in a repair unless you're sure of yourself. Very problematic with the only parts store closer than 30 miles is still 12 miles away.
Sorry-I'm rambling

 

[Road Angels]

I have the same truck with no gas gauge I figure about what I use by mileage, but about every six months I go to the pump and I think its empty or close and it will only take a few gallons , moral of the story with out a true working gauge, you never know whats in the tank or your mileage per gallon cause it varies with every drive

 

[Doofy]

Sorry, but you don't need a fuel guage to figure out your fuel mileage. A gauge has nothing to do with it. You need a fairly accurate odometer. Simply divide the number of miles driven by the number of gallons put in the tank.

For a more accurate accounting I always go to the same station and use the same pump. I set the nozzle on the first click (slow speed) and when the nozzle clicks off...that's it! I do my mileage calculations and then reset the odometer for the next time.

I could stand there for a couple more minutes adding more fuel but that screws up the readings. Being consistent gives the best results.

 

[odeek9]

Sorry, but you don't need a fuel guage to figure out your fuel mileage. A gauge has nothing to do with it. You need a fairly accurate odometer. Simply divide the number of miles driven by the number of gallons put in the tank.

For a more accurate accounting I always go to the same station and use the same pump. I set the nozzle on the first click (slow speed) and when the nozzle clicks off...that's it! I do my mileage calculations and then reset the odometer for the next time.

I could stand there for a couple more minutes adding more fuel but that screws up the readings. Being consistent gives the best results.

Absolutely. That's exactly what I do. I fill up the tank always, turn the odometer to 000 then drive until the odometer approaches 200 miles then go back and fill it up again. This time it was 159 miles divided by 5.1 gallons (I always let it just barely start to spill out of the neck so I know that it's full)) which equals just over 31 MPG. Usually go to the same Chevron station. I may be failing a mini IQ test here (brain cell depletion problem) but I don't think that there are any variables

 

[martin]

As you get older you tend to drive easier, this make a big difference to mileage.

 

[odeek9]

As you get older you tend to drive easier, this make a big difference to mileage.

That's true but I still drive a bit too fast. I appreciate all of the thoughts but I don't believe the answer has been found yet. Perhaps it's a combination of things and/or will remain unexplained. I should be greatful that the mileage hasn't worsened. I did learn something though. I've never run out of gas so have never filled up an entire tank. After reading some facts online I guess my tank is 17 gallons in size. Yet I read a long time ago, and have believed for well over 20 years, that it was 11.5 gallons which is why I always fill it up before I hit the 200 mile range (at the usual 21-22 mpg 200 miles would begin to approach emptying the tank). I still find it hard to believe that I was so wrong re the tank's capacity and for so long

 

[adsm08]

I would suspect that your wildly varying fuel economy is due to reduced amounts of corn in the batches those tanks were taken from.

Corn belongs on the cob, not in the fuel tank. Write your representatives and tell them than.

 

[ab_slack]

That is a wide variation. 21 mpg to 29 mpg seems like a change you might see from city to highway. If driving is consistent that is odd and going from consistent 21 and a jump of almost 50% seems improbable. Even with the amount of alcohol varying the energy content doesn't move that much.

Most likely is an error in the assumptions used in the calculation. Like what you believe the miles or gallons wrong.

Like maybe the odometer is slipping and some digit isn't rolling to the next all the time. Or someone is pranking you and putting some fuel in your tank. Or someone else driving it is putting some fuel in.

Or you have a problem like I did on my 89 BII when full would back up the neck when the tank wasn't full. This sort of thing you would expect would result in too good fuel economy followed by very poor, but if it were happening every time (which happened with my BII) potentially you could be ending up a couple gallons short.

 

[odeek9]

That is a wide variation. 21 mpg to 29 mpg seems like a change you might see from city to highway. If driving is consistent that is odd and going from consistent 21 and a jump of almost 50% seems improbable. Even with the amount of alcohol varying the energy content doesn't move that much.

Most likely is an error in the assumptions used in the calculation. Like what you believe the miles or gallons wrong.

Like maybe the odometer is slipping and some digit isn't rolling to the next all the time. Or someone is pranking you and putting some fuel in your tank. Or someone else driving it is putting some fuel in.

Or you have a problem like I did on my 89 BII when full would back up the neck when the tank wasn't full. This sort of thing you would expect would result in too good fuel economy followed by very poor, but if it were happening every time (which happened with my BII) potentially you could be ending up a couple gallons short.

Well, most of your ideas don't apply as I live alone, no one else ever drives my truck, and the cap locks. I keep thinking that it just has to do with math input. I mean 5.1 gallons for 159 miles is clear enough but you may have hit upon something with the odometer reading. Last week when I looked at it it was 102 miles and can recall that I had a passing thought that I didn't think that I had driven that much since my last fill up.
Or, and I've caught this a couple of times over the years but was able to rectify the mistake immediately, I didn't push the knob in all of the way and, as a result, the miles driven were not completely cleared

 

[Road Angels]

Nobody drives the same speed every day and there are a ton of varaibles that can throw off the math, tire pressure, outside temps, wind, how long your in open loop operation (temp) driving with lights and heater,drive down the road after a few miles and reset the od cause you forgot at the station, so you add up these and you will find over time your math is not going to be precise, if your really thinking that your buring that much extra fuel then pull a spark plug it will be black