Gasoline Evaporation of 3/4 gallon per week ???????

[Brad777]

I have a 1995 Bounder with a 75 gal. gas tank. I am loosing about 3/4 gal. of fuel every week because of what I think is evaporation. I have looked for leaks and find none. I followed the vent tube from the gas tank back to the gas cap area and it looks in tack. The vent tube is a closed loop next to the main gas fill hose. The generator does draw off of the main fuel tank but I don't see any problems with it. I also tried to seal off the gas cap very tight with saran warp to stop the evaporation and that did nothing ? Is it possible that this is normal amount of evaporation ? My climate in So. California is about 75 -85 degrees. Any help on this question would be very much appreciated.

Thanks,
Brad

[Brad777]

Thank you all for the info. I will look for a vent line coming from the top of the tank to a vapor recovery canister. Being that my Bounder is a 1995 Ford chassis I wonder if it would have a vapor recovery unit. I can tell you all that there is no leaks of gas under the rig and 3/4 of a gallon is no big deal except for it is 3/4 of a gallon every week ! It adds up !

[2bzy2c]

Back in the day, I worked at a gas station. Every so often, we would have a customer who would come in and top off his tank a bit at a time for almost 20 minutes. (This was before vapor recovery nozzles.)
The 20 minutes yielded maybe an extra gallon.Some people are obsessed with topping off their tanks.

I would have to agree with some of the comments that you are overfilling your tank, causing fuel to go where it does not belong, such as the vapor canister and the fuel is vaporizing from there.

For the life of me, I don't know how you can tell its missing, or why you should even care, unless there is evidence of a leak. 3/4 of a gallon of gas, spilled on the floor is a significant puddle.

Best of luck.

[Dog_Folks]

Check your friends. It has occurred that "friends" would siphon off a gallon a week for a period of time and then start adding a gallon a week, just to drive the owner nuts!

A game camera may help.

[topflite51]

I would fully expect that the constant topping off of the tank has ruined your vapor canister and probably should be replaced.

[BigRabbitMan]

Brad777 wrote:
Good point on the "no room for expansion" however, I have looked over the fuel system on the rig and the vent tube only goes from the tank to the top of the gas fill area. It is completely closed loop. The only way I see the tank can vent is from the cap or maybe on top of the tank where the Generator picks up the fuel from. I can't see the top of the tank though.

You are not looking at the vent tube others are refering to. Yes, there is the tube that allows air to come up to the fuel inlet that prevents fuel from bubbling back on you while filling. The vent tube that others are refering to comes from the top of the tank and goes to a vapor recovery canister. By filling it up to the top of the fill tube neck, you are causing the problem as there is no room for expansion of the fuel as the temp rises during the day.

Instead, use a dipstick to check the level of fuel in the tank. As you check it over time it will initially drop until it reaches a stablization level. At that point is will be low enough that it no longer goes out the vapor recovery line. You "problem" will then be solved.

[msmith1199]

hmknightnc wrote:

msmith1199 wrote:

Brad777 wrote:
I fill it at home with a small gas jug. When the fuel tank is full it will not take anymore fuel. I then cap it off and wait one to three weeks. Then when I fill up the tank again I measure how much fuel it took to full.

Gas expands and contracts with hot and cold. If you're filling it to the brim you are leaving no room for expansion. As it expands gas will go out the vent tube and then it contracts and leaves you room to put more gas in so it can expand out the tube again.

Bingo! Ding Ding

Ask me how I know this? Okay I'll tell you. Because I'm a private pilot and if you fill the airplane up with fuel in the morning and let it sit out in the sun all day, you can sit and watch the fuel drip out of the vent tube. Now I've never measured to see how much fuel comes out, but at $6 a gallon for 100ll AV Gas, you don't fill the tanks to the rim and watch it leak out. This can actually happen even if you fill it during the heat of the day as the fuel coming out of the truck likely will be cooler from the truck and then will heat up once it's in the tanks on the plane in the sun.

[Brad777]

what is an F53.?

[FuelFunnel]

Brad777 wrote:
Good point on the "no room for expansion" however, I have looked over the fuel system on the rig and the vent tube only goes from the tank to the top of the gas fill area. It is completely closed loop. The only way I see the tank can vent is from the cap or maybe on top of the tank where the Generator picks up the fuel from. I can't see the top of the tank though.

If this is a F53, then yes, there is a vent on top of the tank just right of where the fuel pump is located. It immediately tees off; one hose goes back a short distance and ends with a check valve that only allows air to vent into the tank. The hose on the other end of the tee heads forward to a charcoal canister near the engine. This is an emission control/EPA device that the engine sucks on to burn the vapors that escape from the tank.

Kris

[dennisgt60]

Stop checking it....that'll fix it.

[Brad777]

Good point on the "no room for expansion" however, I have looked over the fuel system on the rig and the vent tube only goes from the tank to the top of the gas fill area. It is completely closed loop. The only way I see the tank can vent is from the cap or maybe on top of the tank where the Generator picks up the fuel from. I can't see the top of the tank though.

[iamcanuck45]

Don't fill it to the top. When you do, the gas expands on a hot day and leaks out the vent tube.:B

[hmknightnc]

msmith1199 wrote:

Brad777 wrote:
I fill it at home with a small gas jug. When the fuel tank is full it will not take anymore fuel. I then cap it off and wait one to three weeks. Then when I fill up the tank again I measure how much fuel it took to full.

Gas expands and contracts with hot and cold. If you're filling it to the brim you are leaving no room for expansion. As it expands gas will go out the vent tube and then it contracts and leaves you room to put more gas in so it can expand out the tube again.

Bingo! Ding Ding

[msmith1199]

Brad777 wrote:
I fill it at home with a small gas jug. When the fuel tank is full it will not take anymore fuel. I then cap it off and wait one to three weeks. Then when I fill up the tank again I measure how much fuel it took to full.

Gas expands and contracts with hot and cold. If you're filling it to the brim you are leaving no room for expansion. As it expands gas will go out the vent tube and then it contracts and leaves you room to put more gas in so it can expand out the tube again.

[deereone]

Over how many weeks have you been checking it? I many times fill within 30 miles of home. Then before we leave again top the tank off from a gas can. I have seen many times where I top off and the next time I check it, it will take more gas. Sometimes after filling I move the unit 2 or 3 feet and can dump in another gallon or two. I sort of figured after filling there is still air in the tank after a few days the gas displaces the air and i can get more in. I've found many times after a station fill I can hand fill from a can 10 to 15 gallons. Don't know just saying.

[Daveinet]

timmac wrote:

FuelFunnel wrote:


If these calculations are correct, he should be able to smell that much loss by walking around his rig.

I wonder if by topping off the tank at home using his portable gas can, he may be covering the internal vent line in the tank with liquid gasoline. As the temperature changes, this raw gas escapes out the vent/charcoal canister. Unless we live next door to a gas station, most of us probably burn a gallon or two just getting back home after a fillup and therefore have a little air space in the tank.

In other words, it might not be possible to keep a gas tank completely full in an unstable environment without somehow sealing the vent lines.

Kris

That was my thought, they had a add on TV here in Vegas for a few years about not topping off your tank at the pump, when the pump clicks off that's all the fuel you need, the rest evaporates off and causes our air quality to go down during the summer, maybe his fuel lost is from filling over full with a portable gas tank every 2 weeks..

That assume that you don't burn off the excess driving home from the gas station. It could be that he burns a 1/2 gallon round trip, and the other 1/4 goes into the canister. The canister is purged when you drive it, so it does not build up stink, when working properly.

I would also suggest another possibility. He could have a stuck injector. The expansion of fuel in the tank will push through a leaky injector and drip into the intake. Since it is burnt off, it goes unnoticed. I would look down the intake. Turn the key, which will turn the fuel pump on to build pressure. It also pulses the injectors. Once the pulse is done, look and see if either injector drips afterword. If it does, the injector is sticking partially open.