Topping off the tank

[MeteorGrayMaya]

Hi everyone, I'm new here! Just got a 2014 GT a couple months ago and I love it.

Anyway, one day I went to get gas and when the pump shut off, I wanted to top off the tank just a tiny bit -- but I was able to get nearly another gallon in there. I know topping off is not recommended in general, but the pump seems to be shutting off prematurely. I've tried smaller top-offs since then and I can still get a fair amount more in the tank, but I haven't wanted to push it as much as that first time.

Does anyone else experience this? Am I setting myself up for a bad time if I regularly top off to get that extra gallon in?

 

[erhayes]

Some pumps just shut off quicker then others. I tend to fill at a medium to fast speed until the first shut off and then do only one slow to finish. I too don't fill too much in case I flood the vent system. One gas station evens warns against over filling. Ed

 

[craigo]

Hi everyone, I'm new here! Just got a 2014 GT a couple months ago and I love it.

Anyway, one day I went to get gas and when the pump shut off, I wanted to top off the tank just a tiny bit -- but I was able to get nearly another gallon in there. I know topping off is not recommended in general, but the pump seems to be shutting off prematurely. I've tried smaller top-offs since then and I can still get a fair amount more in the tank, but I haven't wanted to push it as much as that first time.

Does anyone else experience this? Am I setting myself up for a bad time if I regularly top off to get that extra gallon in?

The shutoff pressure is determined by the gas pump. Some are sensitive and shut off early, in others the mechanism is broken and don't shut off at all. Ask me how I know...

 

[MeteorGrayMaya]

The shutoff pressure is determined by the gas pump. Some are sensitive and shut off early, in others the mechanism is broken and don't shut off at all. Ask me how I know...

The thing is, though, I've gone to this particular gas station for ages, and when I filled up my old car (Chevy Trailblazer) I could only top off like 2 seconds worth of gas. With the CX-5, the topping off goes on upwards of 15 seconds. That makes me think it's a quirk of the car, not the pump...and I don't want to keep doing this if it's going to hurt the car.

EDIT: And yes, I know the obvious answer is "if you don't want to hurt the car, don't top off!" but I am curious if anyone knows what's up with all the seemingly extra room in the tank after the pump shut-off.

 

[erhayes]

Try to not hold the nozzle into the car as deep. That may leave alittle extra room for venting.

 

[madar]

Was a big problem for Hyundais, excess gas from a topoff would find it's way to the charcoal canister. A guy at work spent $2k getting his system cleaned out of his Hyundai, charcoal dissolved and was throughout his Evap lines. Don't know if it's true for other makes, but now I generally stop at the first clickoff.

 

[strongbad]

...Am I setting myself up for a bad time if I regularly top off to get that extra gallon in?

Possibly. Gasoline can easily expand 2% if pumped from cool underground tanks to your warm tank. It's best to leave room for the expansion.

 

[MeteorGrayMaya]

Darn...I was hoping you all knew some secret trick about the tank that I didn't. So much for getting that extra gallon in! But if my worst complaint about the car so far is not being able to get more gas into it, I think I'm fine with that.

Thanks everyone!

 

[piotrek91]

Darn...I was hoping you all knew some secret trick about the tank that I didn't.

The "secret trick" is that there are 2 gallons of gas left in the tank when your range indicator says 0. I'm not saying it's a good idea to use up those last two gallons.. but they are there if you really want to extend the distance between fuel ups.

From service manual:
•When the fuel tank level reaches 6 L {2 US gal, 1 Imp gal} or less, the instrument cluster displays <0 km> or <0 miles>.

 

[MeteorGrayMaya]

The "secret trick" is that there are 2 gallons of gas left in the tank when your range indicator says 0. I'm not saying it's a good idea to use up those last two gallons.. but they are there if you really want to extend the distance between fuel ups.

From service manual:
•When the fuel tank level reaches 6 L {2 US gal, 1 Imp gal} or less, the instrument cluster displays <0 km> or <0 miles>.

Good to know for emergencies! I'll probably never see that happen, though; I drive a lot for work so I'm pretty conservative with my fill-up routine. A couple weeks ago I did see the low fuel light turn on when the range indicator got to 24 miles, but I was heading to the gas station when it happened so it was basically just an experiment and not the start of a habit (I only saw the low fuel light go on twice in the 10+ years I had my old car).

 

[SayNoToPistons]

Possibly. Gasoline can easily expand 2% if pumped from cool underground tanks to your warm tank. It's best to leave room for the expansion.

A bit optimistic... It is actually 1% every 50*F. So if there is any thermal expansion, it would be VERY dismal. You are looking at a few ounces of expansion, and that is during warm seasons.

 

[strongbad]

The volumetric thermal coefficient of gasoline is .000950 /degC., so for 10C (50degF for underground tank) to 32C (90degF car parked on hot pavement) the volumetric expansion would be 2.1%. That's .3 gallon expansion for a 15 gallon tank.

 

[IHeartGroceries]

The volumetric thermal coefficient of gasoline is .000950 /degC., so for 10C (50degF for underground tank) to 32C (90degF car parked on hot pavement) the volumetric expansion would be 2.1%. That's .3 gallon expansion for a 15 gallon tank.

The variables here are likely accurate. At least partially. The 50 degree guess for the gasoline in bulk storage is fair. I'd guess anywhere between 40-50 degrees. But, I'd have to guess that the gasoline in the automobile's tank is likely not warned much, if at all. It is on the exterior of the vehicle, and not stored near any real heat sources.

Assuming we're talking about winter ambient temps here. But, even in the summer, the bulk storage houses the fuel at fairly cool temps, between 75-85 degrees.

 

[PhoenixINX]

The "secret trick" is that there are 2 gallons of gas left in the tank when your range indicator says 0. I'm not saying it's a good idea to use up those last two gallons.. but they are there if you really want to extend the distance between fuel ups.

From service manual:
When the fuel tank level reaches 6 L {2 US gal, 1 Imp gal} or less, the instrument cluster displays <0 km> or <0 miles>.

A few testers have already disproved that fact in the manual, as a couple have ran the tank dry and noted that the miles remaining is wickedly accurate.

Just to self-validate, I ran mine to zero and it took 15.1 gallons. Assuming the 14.8 gallon tank, plus a third of a gallon up the feeder pipe, that sound about right.

Don't gamble if the MFD says 0 miles remaining.

 

[IHeartGroceries]

^For some reason, that is a gamble my silly wife always enjoys taking. I guess it isn't enough for me to plead with her not to run it that low, and it'll actually take becoming stranded before she learns. LOL!

 

[merc3065]

I routinely run down to the point where I can stuff 50-55L in the tank. I have found that after the first click, I wait about 8-10 seconds for the bubbling to stop. This is usually around 40-45L. From that point I slow fill till it clicks off a second time and stop.