What's the deal with the fuel tank?

I've got a 92 GS500 and when I fill it up every few days I can brim it then the level goes back down somewhat, brim it again and it goes back down again, I seem to able to do this endlessly - keep briming it slowley and it'll never seem to reach capacity as the level eventually goes down a enough.

I'm worried it's seeping out a breather or something whilst I'm filling it but nothing I can see (or smell).

Regards

Grab your owner's manual. Section 2-11 where it shows a side shot of the tank.

The bottom of the Sleeve (filler neck) is deeper in the tank. When the level of gas reaches the bottom of the sleeve, the gas comes out of the nozzle faster than the gas in the sleeve can disperse. So the sleeve fills to the brim. That small amount of gas can then slowly disperse into the rest of the tank. But as it is so little, when spread over the rest of the surface area it hardly raises the overall level. So you add some more. It then disperses again, hardly making a change to the overall level. Repeat.

Michael

Quote from: mister on August 02, 2010, 07:06:54 AM
Grab your owner's manual. Section 2-11 where it shows a side shot of the tank.

The bottom of the Sleeve (filler neck) is deeper in the tank. When the level of gas reaches the bottom of the sleeve, the gas comes out of the nozzle faster than the gas in the sleeve can disperse. So the sleeve fills to the brim. That small amount of gas can then slowly disperse into the rest of the tank. But as it is so little, when spread over the rest of the surface area it hardly raises the overall level. So you add some more. It then disperses again, hardly making a change to the overall level. Repeat.

Michael

Thanks for the heads up there, I think I understand what you're saying. So ideally for a completely filled tank I want to keep doing this until the sleeve level stops reducing down, as then the tank is truely full?

Regards

Yup.  It takes forever.. it helps if you put the bike up on the center stand and rock it back and forth a little bit.. I generally make a mess when i try to get it all the way full.. When you fill the neck and let it "disperse" and level out the tank... it needs to let the air escape... but the only place for it to escape is out the neck.. so if you go too fast it bubbles and splashes your paint.

I suppose you could install an Air Bleeder on the top of your tank.. but it might make laying on it uncomfortable.

According to the manual, that sleeve is there so you do not completely fill the tank. There needs to be some air space to allow the gas to expand when it gets hot (like when sitting out in the sun). With no air space, when the gas expands it would start squirting out somewhere.

I would just fill it to the brim once and shut the tank. I see what you're saying about getting the most gas you can, but you're really only going to get an extra mile or so before you hit reserve. I just fill my tank every 100 miles and don't wait for the reserve so I would never even notice that extra little bit.

Quote from: adidasguy on August 02, 2010, 09:10:09 AM
According to the manual, that sleeve is there so you do not completely fill the tank. There needs to be some air space to allow the gas to expand when it gets hot (like when sitting out in the sun). With no air space, when the gas expands it would start squirting out somewhere.

Agreed 

Quote from: sledge on August 02, 2010, 01:13:31 PM

Quote from: adidasguy on August 02, 2010, 09:10:09 AM
According to the manual, that sleeve is there so you do not completely fill the tank. There needs to be some air space to allow the gas to expand when it gets hot (like when sitting out in the sun). With no air space, when the gas expands it would start squirting out somewhere.

Agreed 

Let's make that a double 

Full is reaching the bottom of the sleeve. Maybe one sleeve top up and let disperse and be done with it. Close cap, reset trip meter, pay for gas, ride off. 

Michael

Quote from: tt_four on August 02, 2010, 09:52:01 AM
I would just fill it to the brim once and shut the tank. I see what you're saying about getting the most gas you can, but you're really only going to get an extra mile or so before you hit reserve. I just fill my tank every 100 miles and don't wait for the reserve so I would never even notice that extra little bit.

For me riding mixed aggressive and non-aggressive I usually get 160 to the tank. Not trying to change what you do, but just saying that there is still room to ride at 100 miles.

yes on no overfill, gas on floor of garage is bad. Add cigarette. Whammo.

I just got 215 miles to reserve. Ride maybe a bit wimpy. Not too wimpy. Back roads, lots of full throttle up to 50. 

When you hit the bottom of the sleeve, there is still room for about 0.2 to 0.3 gallons in the tank. The exact amount depends on just how the bike is sitting at the time. I usually fill up with the bike on the sidestand, and squeeze in 0.1 to 0.2 gallons after I hit the sleeve. I do this mostly to try to fill to the same level as consistently as possible, since I track all my gasoline usage. I don't really worry about the thermal expansion of the gasoline, since I have to travel at least a mile after I fill up, and usually much more. Besides, the coefficient of expansion for gasoline is 0.000528/°F. Since the temperature in the underground tank is approx. 60°F, a 4 gallon fill-up will expand to 4.042 gallons at 80°F, and 4.084 gallons at 100°F. Not a big concern, IMO.

Quote from: johnny ro on August 02, 2010, 06:43:37 PM
yes on no overfill, gas on floor of garage is bad. Add cigarette. Whammo.

I just got 215 miles to reserve. Ride maybe a bit wimpy. Not too wimpy. Back roads, lots of full throttle up to 50. 

Boy, I get way better than that..........every staurday and everysunday I go exactly 160 miles round trip to work..........takes 2.4 gallons.........66 MPG......so I could go another 66 miles  (226) and still not need reserve....

Trip is almost constant 55 MPH........maybe one or two red lights, the rest one steady speed..

Cookie

Why the facination to get in that last .1 gallon?  THe bike has an easy 200 mile range........time to pull over and streatch anyway.....

I just fill until the gas hits the neck .......

Cookie

Yep, be careful with that last drop of gasoline.  I know a person who had an accident when the fuel expanded and discharged on an on-ramp.  The discharge was in the path of the rear wheel.. This cost him traction at a critical point in the turn.  The result was an accident with injuries and a totalled favorite bike.  Rider had put 100,000+ miles on that bike, so it was not from lack of experience.

The moral of the story:  I stop at the bottom of that collar every time. 

Have thought about some sort of catch can at the end of the discharge tube, or at least an extension so it's not in front of the rear wheel..