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Old 01-02-2008, 06:35 AM   #1
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Scangauge II users - need some help

I just pruchased a Scangauge II as one of my new toys for the new year. I have some question regarding how people are setting up the Scangauge for their vehicle.

My gas tank is rated for 13.2 gallons. However, whenever I fill up I also top off until I see gas in the filler neck. I did this because it was the only way I gauge verify I filled up to the same point using different pumps. Granted I understand the possible hazards of doing so, I haven't had any ill effects for the past 2 years. Anyway, becuase of this "topping-off" I can fill my gas tank with more than 13.2 gallons, my best guess being I can fit in close to another 2 gallons (~15). Can anyone think of a way to best verify this without running the car until it's completely dry and filling it up?

Has anyone figured out/found some of the additional gauges (Xgauge) for honda cars such as trans temp, etc.?

I haven't yet received my scangauge II but it's on it's way and I look forward to using it. I post some updates when I get a chance.

Thanks!
-D
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Old 01-02-2008, 07:01 AM   #2
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BE careful - a lot of that extra gas you are stuffing into your tank may actually be being sucked back up the fuel pump venting system.

One sure way is to run the tank down to your lowest usual level and then disconnect the fuel line from the engine and CAREFULLY run the tank dry into a gas container and measure it. Just don't overheat the fuel pump running it completely dry.

Usually when the low fuel light comes on you have 2 gallons less. In my xB it came on yesterday and the ScanGauge said I had burned 10.0 gallons and I have an 11.9 gallon tank.
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Old 01-02-2008, 09:15 AM   #3
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With all due respect, I don't understand why one would be interested in filling the tank till the fill pipe itself is full. Especially if using a ScanGauge to measure fuel economy.

OK, that was your old method. It may be time for a new method.

The ScanGauge mesures fuel consumption per injector pulse. How far you fill the tank has no bearing on its measurements or calculations. Further, we don't seem to know how manufacturers determine the fuel tank capacity spec. Maybe to top of tank without counting the fill pipe, but who knows?

Considering the potential losses of fuel when filling to absolute max*, I've decided to fill mine till the first click. That's me. But in nearly a year of doing so I've never had a stupidly low fill up. And when filling at the same station, the cutoff point seems to be remarkably consistent. That is, no unexplained wild fluctuations in mpg calculated every time I fill.

Granted that I don't fill at maximum speed. I squeeze the handle less than half way - enough speed to get past the "slow trickle" range. I don't want a lot of splashing in the tank. This probably helps get a fairly consistent cutoff point.

*Potential losses of fuel when filling to absolute max -
Fuel expands when it warms. Will it expand right out of your tank?
It sloshes when you turn. Right up into the fill pipe?
Pump hose has a suction return system. Will it suck up droplets and vapor you kick up, after they've been recorded by the pump counter?
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Old 01-02-2008, 09:32 AM   #4
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Simple reason for filling it up is I get another gallon in the tank that otherwise would require me to get gas 10% more often and without it would limits my range by about 50 miles less which is a real pain when I barely make it 400 miles on a tank of gas as it is. Actually if I didn't get such great mileage it would be less than 300 miles on a tank of gas closer to 270 miles in fact.
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Old 01-02-2008, 10:33 AM   #5
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My reasons for filling to the neck were as follows:

-To verify the tank was completely full using different pumps.
-To increase my travel range, and have fewer fill-ups.
-To calculate gas mileage with the least amount of error.

As I said before I realize that there were possible adverse effects to filling up the gas tank completely. However, for the past two years I have had no noticable problems requiring me to change this.

The thermal expansion factor for gasoline is 950X10^-6. Calculate a change in temperature of 5 degrees C for 10L yield a difference in volume of ~142mL. Take that to the extreme from 0-25 degrees C and it's plus 712mL. I doubt this will splash up out of the tank. Not to mention that I only fill-up before going somewhere, not on the way home. Any change in volume with thermal expansion will be used up within the first couple of minutes of driving.

As for the fuel pump vacuum system I hold the pump head just outside of the filler neck and fill the tank by just barely squeezing the pump handle. Of course this is done after I'm sure that I've been grounded along with the pump head and my car. The only thing the fuel pump would be vacuuming up is the vapor which I consider acceptable losses.

With that said, as per the scangauge manual, the fuel economy calculations are affected by the amount of fuel you enter into the scangauge upon fill up. If scangauge is indeed calculating the fuel economy based on injector pulses why would the fuel added to the tank be affecting the outcome?
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Old 01-02-2008, 10:51 AM   #6
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perhaps it gas a fuel tank level calculator (warning light?) or options people dont use. probably an estimated range function, mpg x fuel left in tank.

if it used the total fillup data for its calculations, you wouldn't get mpg data until you entered the fillup. tank quantity has nothing to do with instantaneous mpg calculations.
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Old 01-02-2008, 01:56 PM   #7
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What caught my eye while reading this manual was this phrase in the note on page 19 regarding the fill-up correction value:

"The adjustment will take effect immediately and the fuel economy and fuel used will be immediately affected by this adjustment."

While I don't doubt the instantaneous MPG is calculated by the injector pulse, I believe the tank average is affected by this adjustment and when fill-up correction is in place it might off-sets the instantaneous calculations.

Thoughts?
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Old 01-02-2008, 03:40 PM   #8
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That adjustment is for compensating for the amount of fuel the car actually burns to what the ScanGauge THINKS you burn by the injector pulse measurements that is uses to calculate it. It is sort of a fine tuning of the fuel the injectors actually squirt per pulse. You do not adjust that setting until you run a full to full tank of gas and see an error in the reading vs the actual pumped amount of gas. Typically it will be off by a tenth of a gallon depending upon how full you fill the tank each time and the amount of engine braking you did for the past tank of gas burned. Remember that the injectors are turned off during engine braking and the ScanGauge still counts fuel being burnt during that time which adds to what it thinks you burned.
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Old 01-02-2008, 09:38 PM   #9
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Makes sense. cross checks itself.

Quote:
Originally Posted by JanGeo View Post
ime and the amount of engine braking you did for the past tank of gas burned. Remember that the injectors are turned off during engine braking...
in most cars, not all.
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Old 01-03-2008, 12:45 AM   #10
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I'm with brucepick on this, I don't think that the possible "benefits" of fueling till the gas is visible are worth the possible negative consequnces, such as spilling gas and (polluting surface water) or fouling the EGR system (leading to escaped vapors). This is why all the the gas pumps have warnings to not top off your tank.

This does not mean that you have to get variable MPG readings. My personal technique is to nearly always use the same pump at the same gas station. I also only fuel at the first "notch" (the slowest) rate. I get very consistent fill-ups this way.
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