Accurate fuel measuring

[MARTINSR]

I did some searching on the site but couldn't find what I as after.

Forgive me if this is such a nutcase basic question. But how do you measure fuel accurately when it is put into the car? I mean, I am seeing your reports of fuel usage into the tench of a gallon or better here on the site, how in the heck do you know much fuel you have used when anyone of use could fill a car up and come up with a totally different amount of fuel going in the tank (when you break it down into tenths).

Do you just simply let the filler kick off, and leave it at that? You would of course have to average fill ups out being each one on it's own couldn't be that accurate. But do you just "fudge" and say all is good?

Brian

[thatguitarguy]

Originally Posted by MARTINSR

You would of course have to average fill ups out being each one on it's own couldn't be that accurate.

That's it right there.

For any kind of accuracy you have to keep a long term fuel/mileage log.

[tim3058]

I personally hold the pump wide-open til it clicks off. I have started going to the same pump at the same station every time and its eliminated the variation I was seeing from tank to tank (like 8% due to different pump shutoffs). No doubt some set it on the 3rd "auto" notch or something else. As long as you do it the same everytime it should balance out.

[Old Tele man]

...normally I fillup at a brand-name gas station near our house (northwest side of town), but yesterday, because I didn't think I'd have enough gas to make it back home, I decided to fillup at a same-brand gas station near work (south side of town).

...using (A) the same SLOWEST-setting flow on pump-handle and (B) the same "one-click" filling method, I was surprised at how well the SGII fuel value (11.2 gallons) correlated with the new gas pump value (11.238 gallons).

...fast pumping (highest flow rate) is quicker, but tends to create lots & LOTS of gasoline "bubbles & foam" in the tank, making the final "one-click" cutoff far less accurate, because it is 'sensing' the bubbles & foam first and not the actual liquid gasoline level.

[cfg83]

thatguitarguy -

Originally Posted by thatguitarguy

That's it right there.

For any kind of accuracy you have to keep a long term fuel/mileage log.

Yes, I only refer to my 90 day average when I talk about my MPG. Each individual tank only represents a "trend" to me. I try to use the same pump as much as possible, but convenience trumps accuracy. I won't wait for my pump if another is available.

CarloSW2

[Old Mechanic]

I actually listen to the fuel as it gets close to full and reduce the pump flow to about 25% of capacity. First shut off is full, any more and it overflows.

Cars with tanks under the rear seat and 3 foot long filler necks are very susceptible to the slope of the concrete where you park. I try to fill at the same station, but when it is not convenient I try to make sure the slope is away from the filler neck.

On the VX that's left to right and rear to front down slope. The VX filler is behind the left rear wheel opening.

On the Insight the filler is in front of the right rear wheel well and it's almost a straight shot into the tank. Consistent fill ups are much easier.

The wife's old Murano would take another 2 gallons after the pump shut off.

regards
Mech

[thatguitarguy]

It's not good to try to get every last drop into your gas tank because you're just putting it into the evap system which is designed for vapors, not liquid fuel. It's not good to let your tank run empty because the fuel pump in the tank needs to have fuel around it to keep it cooled. Trying to get the most out of each and every tank is not a good practice. Getting the best fuel mileage doesn't have anything to do with overfilling your tank and then running it empty. Just write down how much you put in, and how many miles you've driven, and keep track over a long period of time.

[MARTINSR]

Originally Posted by thatguitarguy

It's not good to try to get every last drop into your gas tank because you're just putting it into the evap system which is designed for vapors, not liquid fuel. It's not good to let your tank run empty because the fuel pump in the tank needs to have fuel around it to keep it cooled. Trying to get the most out of each and every tank is not a good practice. Getting the best fuel mileage doesn't have anything to do with overfilling your tank and then running it empty. Just write down how much you put in, and how many miles you've driven, and keep track over a long period of time.

Yep, tell me about it as I am sitting on the side of hwy 40 in the middle of the dessert in 110 degrees with the family. Done that!

That night at the hotel the guy TOLD ME what I did before I told him! No kidding, I told him how the van stopped and then after a while it started and I drove like hell. He said in his very heavy Indian accent "You fill of up the tank and top it off, you have vapor lock". I had just filled up the tank!

I am thinking just let the filler shut off on it's own and that should be close enough.

Thanks guys.

Brian

[dremd]

I (im my TDI!) add fuel until it's is 1" from pouring out. Vented tank makes it pretty consistent, granted I have no way of measuring what I put in, but thats another story.