Three times in the last 6 fill-ups, the tank would not fully fill. #1, tank clicked off about a gallon short of full, #2, filled properly, #3 clicked off about a gallon short of full, #4 and #5 filled fully, and #6 clicked off about a gallon short of full. All were done with the pump handle set for hands free, at the first (slowest fill rate) setting. At #1, just left without any further action. At #3 and #6, tried to manually add more, pump immediately clicked off, not allowing any further fuel. First issued occurred on June 4. Any ideas?
How do you know it is a gallon short ? Is your mpg about normal ? Using the same pump parked in the same direction ? I almost think you are looking for a problem .
2 Likes
I agree.
Do you know if you fuel gauge reading accurately reflects how many gallons are in the tank? 99.9% of them don’t. Will you fuel gauge accurately measure 1 gallon? I really doubt it. And do you really think 1gallon is going to make a difference?
2 Likes
I know it’s about a gallon short because after every fill-up I check the mileage the old-fashioned way (miles driven since last fill-up divided by fuel taken at most recent fill-up. My normal mileage is between 20.5 and 22.0 per tank. In the last 6 fill-ups the trip mileage was as follows: 25.3, 20.3, 22.6, 25.0, 20.4 and 25.5. The extra mileage noted amounts to about 1 gallon of gas.I make pretty much the same trips between every fill-up.
Using the same pump parked in the same direction? Not necessarily, but the gas station I use is visually flat in length and width. After the first time I noticed this, I made a point of using the same pump facing in the same direction.
No, I’m not looking for a problem. I’ve almost always used the same gas station for the 7 1/2 years I’ve owned the car.
I don’t measure the tank being fuel by the fuel gauge, I consider the tank to be full when it won’t take any more bleeding gas.
I think you have to let it go, no idea what is really going on,but not worth the bother in my book.
1 Like
When you fill the tank the air/fuel fumes in the space above the fuel level has to go somewhere in order to make room for the new gasoline. Assuming this is a modern Jeep the air/fumes are directed into the charcoal canister, where the fuel sticks to the charcoal, and the air is expelled to the outside. Various valves open and close to effect this routing. If all that doesn’t happen, there’s a pressure build up in the tank which switches the gas pump off automatically.
No experience w/your vehicle, but I’m guessing you’ve got one of these problems
- Clog in path from fuel tank to charcoal canister
- Faulty canister
- Faulty evap valve (might be faulty vent valve)
As mentioned above, as long as you don’t mind filling up a little more often, might make sense to just ignore. But me, I’d want to know why, b/c there may be other more serious problems lurking. Just a guess mind you.
2 Likes
Those variations do not indicate a problem . I have some just like that on both vehicles . All it takes is a few extra short trips or hitting most stop lights red. And why are you trying to put that much fuel in your vehicle . I just stop when the pump clicks off . Now if you have trouble putting fuel in your vehicle then there is a problem .
My 2 cents which might explain some of the difference. gasoline, like all liquids, expands when heated. so, if one time you fill up when it’s cool out you may be able to get more gas in than when you fill up when it is hot out.
like I said I am not sure how much of a difference there is but might explain some of it.
2 Likes
Ok. So what’s the math to support your theory? I know there is none, only the “OMG what’s wrong”feeling. And it’s just that….a feeling. At least until you come up with some real proof.
I have an innate sense of how much fuel is dispensed and whether the tank is full or not just from hundreds of times buying gas. I never fill beyond the first click though.even though that may not be a factor anymore. At any rate I would tend to blame the nozzle itself being too sensitive or all that fume containment plastic they have now. Different pump or station would be what I would try. Some stations are super paranoid about gas spills.
I recently had a Camry rental car for about one week, and at first I thought that it must be the most economical mid-size sedan in the world, because the gas gauge never seemed to move. Finally, after driving 90 miles, it moved down a miniscule amount.
When I went to fill it up prior to returning the Camry, the gas gauge read somewhere between 3/4 and 7/8 of a tank, but I wound up putting more than 5 gallons into the 15.8 gallon tank. The bottom line is that car gas gauges are not laboratory-grade measuring devices and they can only be depended on to give you a vague approximation of the actual amount of gas in the tank.
I agree with @weekend-warrior that even though you are keeping most things consistent and it seems that you are using the same nozzle each time, the ambient temperature does make a difference. Also, these nozzles do have a mind of their own.
1 Like
Gasoline only expands/contracts about 1% for every 20°F
So for his 20 gallon tank to take 1 gallon less the temperature of the fuel would have to change by 100°F
If the evap system is working, doesn’t seem like it would matter if the gas expanded b/c of the temperature. The evap system canister would just allow more air to escape through the vent valve. If the canister was full of gasoline of course, for example the purge valve wasn’t doing its thing, then such a problem could possibly develop.
Sorry but that has nothing to do with filling the fuel tank. [Edit: I’m wrong. Newer vehicles have ORVR and use the charcoal canister with the fuel tank vent when refueling.] There is a vent pipe coming out of the fuel tank that comes up along side the filler pipe. When fuel comes up to the vent pipe it creates pressure in the tank which the fuel filler detects to make it turn itself off.
The issue is more likely something like:
- Trying to use the fuel gauge beyond its abilities. Instead, try filling up when the gauge is at a precise location when parked on flat ground, such as exactly 1/2 a tank.
- The fuel gauge is failing and becoming inaccurate.
- A vehicle problem is causing a greater than normal variation in fuel consumption.
- Fuel variation such as ethanol content.
- Changing driving patterns.
- If there really is a problem, then it could be the pump or something to do with the fuel tank vent.
- Edit: Clogged ORVR connected charcoal canister.
You averaged 23.18 for those last 6 fill ups. That’s better than your high of 22!
Have you done the experiment? Try temporarily clamping off that hose and see if it affects filling your gas tank, report the results of the experiment here.
The EVAP or tank vent is a small 1/4" steel line that goes to the engine and charcoal canister in the front. The tank vent for the filler is much larger and goes up along side the large fuel filler pipe.
Maybe it is different for OP’s vehicle, but here’s how it works on Nissans
https://www.nimainfo.com/576/on_board_refueling_vapor_recovery_orvr_.html
It’s apparent somebody has no idea how the ORVR system works.
Tester
2 Likes