Fuel feeding slowly from 2nd tank

[Smithsco]

Folks,

I have a 2020 S-TX GT, which has a factory 2nd fuel tank in the back.

At the start of the season, my fuel gauge never moved until after 80+ miles.

I assumed this is because the fuel in the second tank got consumed first, before the main tank, and I guessed the gauge only registered what is in the main tank, which is why it took some time to drop off the "F".

Last week, and yesterday, I noticed the gauge dropped very fast - I drove only 30 +/- miles, and was showing <1/2 tank, so I stopped and I checked the rear tank, it was still full. After sitting for a short time, the gauge gradually came back some (never to full).

Is the gas gravity fed from the rear to front tank, and based on hills, and angles, does it flow both ways between the two?

Thanks for your input.

Scott

 

[Derek Fosbury]

Folks,

I have a 2020 S-TX GT, which has a factory 2nd fuel tank in the back.

At the start of the season, my fuel gauge never moved until after 80+ miles.

I assumed this is because the fuel in the second tank got consumed first, before the main tank, and I guessed the gauge only registered what is in the main tank, which is why it took some time to drop off the "F".

Last week, and yesterday, I noticed the gauge dropped very fast - I drove only 30 +/- miles, and was showing <1/2 tank, so I stopped and I checked the rear tank, it was still full. After sitting for a short time, the gauge gradually came back some (never to full).

Is the gas gravity fed from the rear to front tank, and based on hills, and angles, does it flow both ways between the two?

Thanks for your input.

Scott

Funny, I've noticed the same thing. When my '22 ST-X was new, gauge wouldn't move for a long time, but recently I've experienced what you describe. I was going to note it to my dealer when I take it in next time, but now curious if this is a more common problem, or if this is the way it's supposed to work.

 

[STAIN]

I am debating on getting an ST-X. I was wondering if you could put a shut off valve on that rear tank to save the fuel for later or siphon it out for emergency.

 

[Derek Fosbury]

I am debating on getting an ST-X. I was wondering if you could put a shut off valve on that rear tank to save the fuel for later or siphon it out for emergency.

The top of the auxiliary tank is fully accessible by taking of the cover and the inside tray, so I'm sure you could do that pretty easily. I'll take a picture on the weekend.

It's still working, i.e., the gas eventually drains from the auxiliary tank, it's just working differently than I expected. The range is pretty good. I haven't run it dry, but by extrapolation, I think I would get close to 300km.

 

[ksiesel]

I think you need to be a bit careful with the shutoff valve idea. I’m not exactly sure how the second tank on the STX works, but I‘ll relay an experience from Corvette’s that use two tanks Where a shutoff valve would not be advised.

In the C6 corvette, they have two 9 gallon tanks right behind the driver and passenger seats. There is a fuel gauge in each of them. The fill port is only on the driver side. There is a large diameter pipe running from left tank to right tank that is used for the filling process. There are also two smaller diameter hoses that handle the pump flow between the two. There is only one fuel pump and that is in the left tank. Part of the flow from this pump feeds the engine, but the other part is sent over to the right tank and runs through a Venturi pump to pull gas from the right to the left tank. The right tank is always empty when the vehicle is under 1/2 total capacity.

My point here being that you may not be dealing with a gravity system and a shutoff valve may cause you issues with the pump since that flow was intended to feed something like a Venturi and now is simply blocked by the valve. I would advise proceeding with caution until you understand the components in the system and how they are supposed to operate.

 

[maim]

well when dealing with older sleds that an extra tank was added to, usually the vent line from the front/main tank is run to the suction line on the rear tank. the rear tank is vented normally. the pump creates the suction on the vent line and plumbed the way i said, it will empty the secondary tank 1st by keeping main tank full. i would check the vent on the secondary tank for ice 1st and then check the line going to the front from it for rub marks/pin holes.

 

[basic700]

Did anybody find the solution to this problem!? I have a 18 stx dx and the rear tank stays full. Wondering what I can do to fix it. It worked fine last season

 

[Smithsco]

If your back tanks stays full, you may have a pinched line or something, as my back tank never stays full - the issue was that I would notice the guage was dropping quicker some days, while other days not move at all, going roughly the same distance, however, when I stopped for a few minutes, the fuel seemed to "catch up", I'd hop on, and the guage was showing full again (or, quite a bit more than what was showing when I stopped). Pretty sure I can hear the vacuum working when I shut the engine off.

Different tempratures seemed to impact it too - although, that may have been my imagination, but the warmer the temperature was, the slower it seemed to fill - Also, at someone's advice, I make sure both caps are tight making a good seal for the vacuum to work properly.

 

[basic700]

I rode it one day last season and it worked as it should. This year. It came out of summer storage/ warm shop/ getting serviced, to out side sub zero temperatures. I rode it 3 different tank fill ups and was having the issue, by the 4th fill up it did finally suck about 2-3 gallons out of that back tank finally. I checked all my lines with air gun, so if anything was plugging vents or lines I got it cleared. Still didn’t work between #2 and #3 fill up. Gas caps not being tight enough might have something to do with it. Hopefully we get some more snow and can see if it starts working as good as it did last year

 

[Smithsco]

Not sure if this is my imagination or not, but also seems to work better when riding solo