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

[MarkS2]

Gas cap was replaced with a new lockable cap. All the gas lines have been inspected and no leaks have been found...

[BrianinMichigan]

Did Brad777 ever find out his issue?

[rgatijnet1]

Since it is a sealed system, have you replaced your gas cap? Is the rubber hose going to your generator leaking? Has the rubber hose from your gas fill to the tank deteriorated?

[MarkS2]

I fill the tank and stop filling when the auto-shutoff occurs on the pump. When the tank is "full", I can usually drive about 40 miles until the needle on the gas gauge drops below the "full" line which equates to about 6 gallons (at 7 miles / gallon). This is how I first noticed the problem - I would take off on a trip and my needle would be below "full". On several occasions I immediately stopped and filled up the tank to determine how much gas was missing. It is pretty obvious when I store the motorhome for 6 weeks and the tank is only at 3/4 full after parking it w/ a full tank. I suspect is is evaporation, but can't figure out where/how it is evaporating from and I would also expect an engine fault light if I had some kind of hole in the top of my tank (which I am unable to see)...I had several people tell me that gas could/would not evaporate that fast. (as an experiment, I placed a gallon of gas into a bucket under my motorhome the other day and when I came back 10 hours later, about 75% of the gas in that bucket had evaporated....)

[cjoseph]

Old thread revived but I have a thought.

Ethanol might evaporate through the smog stuff more easily, maybe? Yeah, blame it on ethanol.

[rgatijnet1]

How do you measure the fuel that is "lost"?
Do you fill up the tank until it is just about flowing out of the cap or do you stop when the pump FIRST stops automatically. If you overfill your tank, some of the extra fuel will immediately go to the canister that on some vehicles is used to absorb gasoline fumes. The newer fuel systems are sealed so evaporation is not happening but if you overfill your tank in cool weather, you can count on some fuel leaving your tank due to heat expansion when it gets warmer.
Personally I don't know how I could accurately measure such a small loss on my 75 gallon tank.

[mtrumpet]

Old-Biscuit wrote:

Dog Folks wrote:
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.

:B

Did that to a supervisor in early '80s.
He had bought a new Volkswagen. We added gas. He kept bragging about the fantastic gas mileage.
Then after he took it in for free tune up/oil change etc. after breakin period we siphoned gas off.
He took it back to dealer and complained.....asked then what the heck they had done to ruin his gas mileage.

:B:B:B:B:B:B

[MarkS2]

I started seeing a similar problem about 6 months ago on my 2002 E450 Coachman motorhome. I always fill up the gas tank when I return from trips and started noticing that I was missing gas when I started my next trip. I appear to be loosing 2-3 gallons of gas per week (the rate of loss seems to be somewhat consistent regardless of how long I store it.) I am not seeing any leaks where I park the vehicle. Then thought someone was stealing the gas and added the lockable gas cap. Last month I took it to the Ford garage and they could not locate any leaks or smell gas under the motorhome. They also checked the computer for engine code faults and did not find any. I'm stumped. Does anyone have any suggestions?

[msmith1199]

Brad777 wrote:
The most I have gone is three weeks and it was 2.25 gallons loss. In the past I have gone months and that is when I decided to start my test.

Well why didn't you say this before. Sounds like you have a gas leak! You should get that fixed.

[BigRabbitMan]

Brad777 wrote:
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 !

My coach is a 1976 and it had two vapor recovery canisters (due to size of tank) so I can guarentee that yours has at least one and possibly two. They have been required for a long, long time.

Stop overfilling the tank and the gas will stop disappearing and stop "adding up".

[Jagtech]

As winter ends and summer temperatures begin to rise, your steel gas tank expands. Thus the lower level of gas.

[Old-Biscuit]

Dog Folks wrote:
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.

:B

Did that to a supervisor in early '80s.
He had bought a new Volkswagen. We added gas. He kept bragging about the fantastic gas mileage.
Then after he took it in for free tune up/oil change etc. after breakin period we siphoned gas off.
He took it back to dealer and complained.....asked then what the heck they had done to ruin his gas mileage.

[Brad777]

The most I have gone is three weeks and it was 2.25 gallons loss. In the past I have gone months and that is when I decided to start my test.

[msmith1199]

Brad777 wrote:
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 !

How long do you let it sit between uses? Trying filling it up and then just leave it alone for however long you can then see how much is missing. I'll bet no matter how long you leave it you'll find it takes 3/4 of a gallon every time to top it off because that's how much goes out the overflow. Once that 3/4 is gone, it will maintain that level.