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fourgivn1
Dodge Dakota
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1/24/2002
12:19:31
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 Subject: Pressure in gas tank
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It's already well established that for some odd reason a load of us have 22 or 24 gallon gas tanks that won't let us put anywhere near that amount of gas in there. (I've managed to 'stuff' 18 gallons in mine, and I guess since I can go about 300 miles on one tank, that means I am getting about 17 MPG at the worst, which isn't too awful.) I took the gas cap off of my tank to fill up this morning (I had maybe 30 miles left in it) and was greeted by a "psssshhh!" coming from it, as if someone had pumped some air in the gas tank. Can anyone shed some light on this for me, as to whether this is normal? Don't like the thought of 20 gal of gas building up pressure.
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Graphite
DakotaEnthusiast
1/24/2002
12:44:43
|  RE: Pressure in gas tank
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The owners manual says to remove the gas cap slowly to relieve any pressure that may have built up. Look at it this way- when you put gas into a gas can and leave both ends closed, by the time you get the can home, it will hiss when you open it. I am sure the fuel line has a breather valve, but some pressure could build up. BTW I have run out of gas once with a 22 gallon tank and refilling it took just over 21 gallons. The gas tank expands and contracts depending on the weather. I wouldn't worry if I were you.
~JOE~
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fourgivn1
Dodge Dakota
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1/24/2002
14:26:43
| RE: Pressure in gas tank
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Well, I definitely know that some pressure will build up; just seemed a tad excessive. However, I WOULD like know why it is that I have only managed to stuff 18 gallons into the tank. That is THE MOST I have managed. Is there any way to correct this? I mean, I can deal with it, but hey, if it says 22 gallons, I would kinda like to get within a gallon of that.
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Graphite
DakotaEnthusiast
1/24/2002
15:02:15
| RE: Pressure in gas tank
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How low do you let the gas get in your tank before you fill up?
~JOE~
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Dakaty
GenIII
1/24/2002
15:45:45
| RE: Pressure in gas tank
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4given1
The next time you get low on gas, carry a gas can with a gallon of gas in it. When you start to run out of gas, add the gallon and go fill up. Then you will know how much it holds. Also, you will see how your gas gauge reads relative to being empty.
I've had cars that ran out of gas as soon as the gauge needle hit the "E". I've also had cars that would run 100 miles after the needle fell below the "E".
Bill
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sandman
Dodge Dakota
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1/24/2002
19:11:17
|  RE: Pressure in gas tank
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Well 22 or 24 gallons is what it would take to completely fill the tank. Your sender is designed to read empty well before you run out of gas. There is propably 4-6 gallons of gas in that tank when it reads empty. their is probably 2 gallons of useable fuel in the tank that your sender/FTP Module can not pump.
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Dave Mitchell
Dodge Dakota
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1/24/2002
19:58:59
| RE: Pressure in gas tank
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Mine lights the warning light when there are 5 gallons left in the tank. That will allow me another 100 miles of "reserve" to find a gas station. I like it that way.
I've gone 430 miles on a tank without running out.
I average 19MPG with the 4.7, 5-spd, 3.55 gears, and tire & handling package in our '01 4x2 Quad Cab and have gotten up to 23.5MPG.
I wonder what it would have gotten with the standard wheels/tires?
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Bruce P
Dodge Dakota
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1/24/2002
20:10:23
| RE: Pressure in gas tank
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(fourgivn1) To answer your question about the pressure in the gas tank.
The OBD2 (OnBoardDiagnostics version2) contains a diagnostic that checks for leakage in the EES system (Evaperative Emmissions System). To keep this answer short.... suffice to tell you that there is a pump that pressurizes the gas tank slightly then seals it and times the bleeddown time.
I suspect you stopped for gas in the middle of the diagnostic.
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mopar67
Dodge Dakota
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1/24/2002
20:59:03
| RE: Pressure in gas tank
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Also, to combat the rash of fuel pump failures when detroit started placing the fuel pump in the tank, they build in some reserver so you are never truly empty. The gasoline acts as a coolant to the fuel pump.
WHen fuel pumps where mechanical, this was not needed. Older mopars I ran were dead on in that when the needle said "E", you were OUT!
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sandman
Dodge Dakota
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1/24/2002
21:57:23
| RE: Pressure in gas tank
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I need to make a correction to my post. It should have read 2 gallons of unusable fuel. P.S. According to product specialist at A/C Delco if your electric fuel pump runs for as little as 20 sec. with out gas it will be permanately damaged. It can be enough to seize the pump. Most ecm's will shut off fuel pump after 5 sec.'s if pressure does not come up.
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Todd W
Dodge Dakota
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1/25/2002
10:33:36
| RE: Pressure in gas tank
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I get that occasionally too, but only after driving for a while with the light on or after a big temperature/weather change. I always attibutied it not to pressure, but to a vacuum because the truck was 'sucking fumes'. I always suspected this since, when removing the gas cap, there was never any feeling of outgoing air movement or signs of escaping vapor or excessive gas fumes (which should be present in a pressurized blow-out of gasses).
Honestly, every car I've ever owned has done that when driven around on E for a while. From the '77 Chevelle to the '86 and '96 Cavaliers...
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Yo
Dodge Dakota
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1/25/2002
10:56:48
| RE: Pressure in gas tank
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When I first bought my dakota, the fuel light would come on with about 6 gallons left, then all of a sudden it would come on with about a gallon or so left.
I put about 22.5 gallons in my 22 gallon tank once. The pump shut off and I topped it off a bit. can anyone beat that?
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Joel
Dodge Dakota
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1/25/2002
11:21:32
| RE: Pressure in gas tank
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You can do about $500+ in damage on some cars, like the Camaro and Vette if you run out of gas and keep starting or keep the igition on. Pump is about 300 plus labor. Your curiosity could cost you some money. If the engine dies, kill the ignition right away and put the gas in before attempting to start it. That way the pump wont burn out from being overheated due to lack of coolant/gas.
Joel
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