Refueling Variables

[Green GX]

I stopped by the CE station in Santa Clarita last week to fill up. When I got there, there was a trash truck filling at the time. In the past I've gotten a lousy fill when this happens. This time it was 97 degrees F. out, but my gauge showed a solid 20 bars when I finished. (It turns out I went just over 248 miles on that tank and still had 3 bars lit up when I filled the tank below.)

The next time I used the station it was 94 degrees F. and no one else was there. The tank only filled to 19 bars that time. I don't recall how many bars were lit up on the gauge before I started with the trash truck there, but there were only 3 bars lit up prior to pumping this time.

So, I figured I'd let the gas cool off and come back the next morning to top off the tank, then figure my mileage with two "full" fills. The next morning I filled the tank again, (65 deg. outside,) but it only filled to 19 bars again.

I'm a a loss as to why I can't get the tank to fill completely on the two last trips to the station. The hot/expanding gas theory doesn't seem to hold and neither does the hot outside air temp; two common theories for lousy fills.

Anyone got any ideas?

Bill

[CraziFuzzy]

Re: Refueling Variables

I'd be willing to bet that just because there wasn't a truck there filling when you were there, doesn't mean that the station hasn't been on high demand for a while before you got there. The stations don't top off right away after they get sucked down, the compressors are sized to meet the daily demands, throughout the day. This is especially true for the stations that have a slow-fill system for the local fleet.

[Green GX]

Re: Refueling Variables

I'd be willing to bet that just because there wasn't a truck there filling when you were there, doesn't mean that the station hasn't been on high demand for a while before you got there. The stations don't top off right away after they get sucked down, the compressors are sized to meet the daily demands, throughout the day. This is especially true for the stations that have a slow-fill system for the local fleet.

That's entirely possible. Before I use a pump, I'll take a look at the amount last pumped. If it's 40-50 gal. I know there's been a big truck there. (or a Godzilla sized GX ) There are 4 pumps at the Santa Clarita station and I didn't look at the other 3.

Bill

[Green GX]

Re: Refueling Variables

Me again.

I noticed the last time I filled at the Santa Clarita station that the gauge was "flirting" with with the 20th segment being lit up when I was done. By "flirting" I mean that after filling when I start the car the 20th segment is lit, but goes out in about .5 miles.

So, when I figured my mileage I added .4 gal because the 20th segment didn't stay lit very long. The mileage worked out to be 43.2 mpg. I returned this morning and topped it off, (20th segment stayed lit,) adding the additional miles and gge to yesterday's figures and lo and behold, I got 43.2 mpg.

I'm wondering if by adding .4 gge for every segment that is out on the gauge when you figure your mileage, this will give you a good mileage estimate?

Bill

[Curtis]

Re: Refueling Variables

2 things:
1) if you can buy gas at $2.25 a gge in San Fernando, why would you fill up at the CE site?
2) if one of our inordinately bright members can do the math and tell you roughly what the difference (shrinkage if you will) is once the fuel drops in temperature. Of course this will vary with ambient temperature, but assuming the fuel tempp rises to 140 Degrees f. during fueling and cools back down to 90 degrees f. after cooling. What does this do to his .4gge theory?

[Green GX]

Re: Refueling Variables

2 things:
1) if you can buy gas at $2.25 a gge in San Fernando, why would you fill up at the CE site?
2) if one of our inordinately bright members can do the math and tell you roughly what the difference (shrinkage if you will) is once the fuel drops in temperature. Of course this will vary with ambient temperature, but assuming the fuel tempp rises to 140 Degrees f. during fueling and cools back down to 90 degrees f. after cooling. What does this do to his .4gge theory?

1) I'm locked in at $1.999/gge at CE stations for 18 months.
2) I think Boyle's Law uses temp/pressure to tame those wild variables. I don't think it takes into consideration trash trucks or buses though.

I have a few observations that make me believe just pointing to one variable doesn't explain the whole story.

a) I've waited 15 minutes after filling at a station, (San Fernando,) on a 74 degree day then, I tried to top off the tank. (only 19 segments lit) The resulting top-off? .25gge. As I recall, the pump was pumping at over 3600 psi. Plenty of pressure, time for the gas to cool and filled on a cool day, yet only 19 segments.

b) If the gas is hot after filling, and it's a hot day (90 deg.+) shouldn't my gauge show fewer segments lit up the next morning after the gas has a chance to cool down overnight? Mine doesn't.

c) I've left a station after filling up with 20 segments lit up. Typically within 1 mile that 20th segment goes out. I have actually stopped at a red light and seen the 20th segment light up again! But, then it goes out shortly thereafter. We know the gas gets hot going into the tank, then cools. That seems to explain the 20th segment going out as the gas cools. But, did it heat up again, come back on, then cool and go out?

Curtis, can you find out from the service techs whether the OBD II system logs a sensor that reads pressure in the tank? If so, I'll contact the people that make the ScanGaugeII and see if they can reprogram their box to ping that sensor and display the result. That would remove one unknown from the equation. (least for me)

Bill

[Curtis]

Re: Refueling Variables

*I'll try and find out about a tank sensor...
*the gas guage is actually a temperature compensating pressure guage...
*I've gotten as much as an additional gge after an overnight cool off, much less with an hours cool down. I think being insulated in the trunk may have something to do with a longer cool down.
*and I don't play with CE anymore... too greedy for me.

[jetboatjohnny]

Re: Refueling Variables

I always get at least one GGE, and up to 1.5 topping off a day later and after driving 8-10 miles.

[Green GX]

Re: Refueling Variables

I always get at least one GGE, and up to 1.5 topping off a day later and after driving 8-10 miles.

Johnny,

I checked my receipts and in my drive from the Santa Clarita CE to home and back to top off I fill with from 1.3-1.8 gge. (38.7 miles round trip)

Bill