Hi all,

I wanted to share an experiment I have been running for the last 3 weeks that seems to lower my fuel costs... it has been pretty consistent the last few weeks - I'll explain below:

- When I first started driving my truck, I noticed that on a FULL tank of gas at the beginning of the week (Monday morning), driving to and from work for the entire week, my gas guage would be a tad under 3/4 when I arrived in my driveway on Friday afternoon. This would tally around $38.XX (CAN) to bring the guage back to full. Therefore, driving to work costs approx. $38.XX

- During the week, I would notice that my gas guage would take awhile to come down from the FULL position (e.g. 3 full days of driving), but once it reached halfway between FULL and 3/4, the guage would lower quicker and stop at a tad under 3/4.

- I decided to perform a little experiment. I filled up my tank and waited for Monday morning. I then drove until Wednesday afternoon where I filled the tank back up - $16.XX to bring to FULL. On Friday afternoon, I then filled up the tank again to wait for Monday 14.XX

- So the first time, I noticed I saved $8.XX or so dollars.

- I ran the same experiment and noticed I was saving between $8-9 dollars a week by topping up the tank in the middle of the week.

THE QUESTION: It seems by having the tank at the fullest saves me money as the truck doesn't use as much gas??? How can this be? You would think the more fuel, the heavier, the more fuel you would be using?

I'll keep this updated, but what are your thoughts on this?

Please note the gas prices varied around 3 cents and driving style was the same.

 

Did you mean to say under 1/4?

This is interesting, if this continues let me know and ill have to start doing this because i do notice that i get more miles from full to 1/2 tank than i do from 1/2 to empty

 

No, 3/4

 

k sorry, the wording is just slightly confusing when you say once it reached half way. what halfway are you referring to?

 

Two things here I think.

Number one...the gauge could be more or less accurate at the top of the tank than the bottom end. Probably is.

Two...it is a fact that a fuller tank...less sloshing around inside last longer. Less sloshing around is less vaporization of fuel. thats why most tanks have baffles inside to minimize fuel movement.

Honestly I think it is 6 of one or half a dozen of the other. If it makes you feel good keep doing it that way.

 

Well, if it saves me 8.50 a week = $442 a year, I might as well do it

 

Refill everyday and save $24.

 

I have never really tried this experiment but I do know that every vehicle I have owned takes forever to come off of Full but once it comes off of it, it seems to disappear a whole lot faster. If it works do it.

 

I was going to do a trial the other way.. see if my truck does better from 1/2 full to empty rather then from full to half. My thought is lugging the extra weight is counterproductive. I think you should redo the full tank, no fill ups till friday again to see if maybe your truck has broken in, and that it's not just the natural progression of fuel economy from new.

 

Perhaps your foot is gentler on the gas pedal or you did less errand runs, giving rise to you belief of a fuel savings. The engine's fuel consumption shouldn't differ so drastically between partial and total filled tank.

 

Are you checking your mileage based upon the fuel gage reading or doing the mpg check based upon how many gallons you used to fill it back up versus miles driven?

When I check mileage I try to shove the pump nozzle the same depth into the tank when filling. Then fill until the pump will click off at the handle. Using the gage alone can be misleading - especially if you overfill a bit.

 

if you are really going to do an experiment like this you should use a measurable value like mileage rather than the fuel gauge indicators. But i guess maybe you too and from work is a consistent and measurable X value. Just tough to understand the full tank, 3/4 tank, 1/2 tank references.

 

I had a 87 and 89 f150 with the 300 six cyl and if you let the tank get below 1/4 the engine had spark knock.Its like the octane was lower or the ignition timing increased when you reached 1/4 tank.This does not make sense but it happened.Strange things happen.Both trucks had dual tanks and it did it on both tanks.I was using two tanks a week so the gas had little time to go stale.Maybe its the lack of baffle in the tank thing?

 

its probably bc your when your tank is full it is actually past the full mark..kinda of like when your on empty and the needle goes below the e mark but for some reason has extra gas..i think the first and last quarter arent accurate in that aspect and that if you did the same experiment with the 2nd and 3rd quarters youd find that they are the same....but you would think the less gas you have the more you save just by losing the extra weight in the truck

 

I suspect that the OP is assuming that since his commute is fixed that he is driving the same number of miles between the one fillup case (fillup on Friday) and the two fillups case (fillup on Wed and Friday). OP key thing to confirm is that you did drive the exact same number of miles between Mon and Fri in both scenarios.

If you did, and you still find such a drastic improvement in mileage, my guess is that the point at which the gas nozzle 'clicks' to indicate FULL has a huge margin of error - nothing else.