How to estimate fuel consumption - best method! - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

Christ · 10-11-2009, 02:36 AM

I used to laugh at my Aunt and Uncle for "topping off" then driving home... hot summer day, you could see the gas literally running out of the tank of their Mazda MPV minivan. Right back out the filler neck, past the cap.

After they had it for a couple years, the paint was completely gone below the filler neck area, and it was beginning to rust through without warning, before the paint even started coming off. It quickly became garbage, just like every other vehicle they drive (including the Prius).

Frank Lee · 10-11-2009, 02:44 AM

That's a shame. They never did put two and two together eh?

OK I thought of a bit of proof re: first click bad. Sometimes after first click it takes quite a lot more to get to the second click, and sometimes not.

Christ · 10-11-2009, 02:59 AM

Proof for second click:

When the pump clicks, it's because fluid has re-entered the nozzle, changing the pressure required to flow the fluid into the tank. If it continues pumping after it's clicked the first time, it wasn't full. It will always stop at/near the entry point of the nozzle, within a few pennies' worth of fuel.

The remaining variable is nozzle depth. Most people just shove it in there to the hilt (LOL), so that's not really a variable either, since it's controlled as precisely as is easily possible.

Variances in vehicle angle, if subtle, will again, only mean pennies, if even that much. The filler neck is always the highest point in the tank, and as long as you didn't leave a massive air bubble in the tank because of an off-kilter angle, the variance in fills will only be the volume necessary to fill a small section of the throat near the fill nozzle.

Same thing goes for pump selection, because, again, they're setup to shut off when the pressure across the nozzle changes. For the same reasons as above, the variance in the filler neck will only be pennies.

For all those reasons, I just don't even pay much attention to where I fill up anymore, or how I do it. My variances are within a few tenths of a MPG normally, except when I start using my vehicle as more than a commuter, or making long trips. Then you'll see huge variances of several MPG (up to 10 at times) in my logs.

I haven't even been keeping the logs the way I should on Cara because of these types of tank variances, I've been doing alot of hauling of heavy stone and other materials w/ Cara.

groar · 10-11-2009, 04:46 AM

All my fills in megane's log have been at the same pump, same orientation and with a 6 seconds wait after the 1st click.

I have been doing 2nd click for more than a year. The quantity between 1st and 2nd click has been between 0.2 to 2 L => 1.8 L / 50 L = 3.6%

Since summer I'm doing full tanks : until I see the diesel. Between 2nd click and full tank there has been between 0.9 and 1.1 L => 0.2 L / 50 L = 0.4%

Denis.

Cd · 10-11-2009, 11:25 AM

I know that my tank holds somewhere between 10.5 and 11.2 gallons of fuel.
As I get near 9 gallons, I slowly release the trigger to reduce splashing. I then give it fuel in stages. I try to shut off at the first click. *

If you do your math, and the figures just seem a little too high or low, the pump reading may be off. I once filled my tank and found out that the meter was off. The reading had indicated that I had filled up with less fuel than I did. This resulted in an error of several MPG. I therefore would try more than one pump.

One thing I also do is to try and fill in the mornings when the air is cool. This reduces the release of fumes from the tank.

*The problem with this is that a lot of the gas pumps around here do not shut off when they are supposed to, and you never get the 'click' . Instead, it just spills all over your car.
The emissions that result from this are extremely bad since the vapors are going straight into the atmosphere without any filtration. ( Most likely creating more pollution than you would create driving for several miles. )

Christ · 10-11-2009, 12:42 PM

Quote:

Originally Posted by Cd

I know that my tank holds somewhere between 10.5 and 11.2 gallons of fuel.
As I get near 9 gallons, I slowly release the trigger to reduce splashing. I then give it fuel in stages. I try to shut off at the first click. *

If you do your math, and the figures just seem a little too high or low, the pump reading may be off. I once filled my tank and found out that the meter was off. The reading had indicated that I had filled up with less fuel than I did. This resulted in an error of several MPG. I therefore would try more than one pump.

One thing I also do is to try and fill in the mornings when the air is cool. This reduces the release of fumes from the tank.

*The problem with this is that a lot of the gas pumps around here do not shut off when they are supposed to, and you never get the 'click' . Instead, it just spills all over your car.
The emissions that result from this are extremely bad since the vapors are going straight into the atmosphere without any filtration. ( Most likely creating more pollution than you would create driving for several miles. )

I'd keep using that pump and find another way to calculate my MPG... if it's ripping off the oil company, I'd be all over it. They've been pick-pocketing us for how long?!

bombloader · 10-11-2009, 05:00 PM

I've just switched from first click to second click with the Jeep. Haven't had enough fillups to tell if it reduces variance. With the motorcycle, I just fill until gas is hits the bottom of the neck. Can't wait until the nozzle clicks off, it'll spray me with gas first. If I shoved the nozzle all the way in, it would probably cut the capacity in half

Fillup technique definitely matters, I get a lot variation on my trips thru OR, where you can't pump your own gas. I try to tell the gas station attendants not to top me off, but I think some of them do it automatically. Glad I don't live their anymore, its a bit frustrating not to be able to control the fillup when your tracking mileage.

Christ · 10-11-2009, 09:34 PM

I think with the bike, I'm just going to figure out the tank capacity, then divide up gas into cylinders that handle that much fuel (or a measured amount less) to reduce variance in fill ups. Besides, I shouldn't be going anywhere far enough to have to use a gas pump with it.

99LeCouch · 10-11-2009, 11:12 PM

I fill from the same pump at the ethanol-free station around the corner. 3 clicks will get my tank full with 17 gallons of fuel assuming I run it down to 1 gallon remaining. What can I say, I like living dangerously!

Christ · 10-12-2009, 12:20 AM

I used to run my tank low to get the crap out of it and into the filter. If you do it all the time, you don't screw up the pump the one time you run out of gas. Since then, I realized that for the short amount of time I usually own a car, it doesn't really make any difference.