Different Way to Plumb Dual Fuel Tanks

[Sharecropper]

I'm in the process of installing an auxiliary fuel tank on the passenger side of my M1028 and am considering a different way of plumbing the two tanks.

While thinking about the valving and switching between the two, I wondered why the two tanks couldn't simply be plumbed together for one 40-gallon fuel supply. The supply lines from both tanks could be joined with a Y connector, as could the return lines, and the vent lines could be connected between the two tanks. This plumbing design would allow equilibrium between both tanks so that the fuel level on both sides would stay the same. The dash gauge would still indicate the same fuel level in the OEM tank, it would just be indicating the level of 40 gallons instead of 20. Am I missing something? Why wouldn't this work?

 

[rumplecat]

If the tanks are at the same level, I don't see why it wouldn't work.

 

[antennaclimber]

Are you going to draw fuel from the top of the tanks?
If you do, one would think that it should draw an equal amount of fuel from each tank. However, I am not an engineer on this subject.

A potential problem comes when refueling, you will need to add fuel to both tanks at each fill up. The tanks will not equalize if you only fill one of them. The fuel will not go up the draw tube and back down into the other tank. You could run out of fuel in one tank if you do not add fuel to both. With this in mind, the fuel gauge will only show the level of the tank with the fuel gauge.

If you add a tube between the two tanks at the lowest level, they will maintain a equal amount of fuel in both tanks. But then you have a potential snag point when going thru rough terrain.

I added a second fuel tank to my M1008, along with a second fuel gauge and an electric pump on a momentary switch so I can transfer fuel from the aux tank on the passenger side to the main tank on the drivers side.
Filling up both tanks is not much fun. You need to fill up on one side then turn the truck around to fill up the other side. I had people pull in and take the pump I was using while I was turning around. If you go to a truck stop that has fuel on both sides, it's easier but then you are competing with large trucks for an open pump.

 

[Jeepadict]

Road tractors (semis) have done this very thing since the dawn of Diesel. Old ones drew from a single side and had an equalizing line at the bottom of the tanks. Modern/current more closely resemble exactly what you're describing but with more intricacy with mismatched tank sizes. I say try it, worst that can happen is it doesn't work and you have to go to plan B. Send it

Sent from my SM-G970U using Tapatalk

 

[98G]

Consider what happens if you park on a side slope. Potentially the fuel from the higher tank drains into the lower tank and it overflows.

I'm sure there are ways around it.

 

[nyoffroad]

Instead of one tank on each side install a Blazer or suburban tank in the rear and turn in around so the fill is on the left side. Use the fuel door a surrounding metal from the doner truck to finish the outside. As far as connecting them together I'd keep them separate and use a transfer pump and momentary switch like AC did.

 

[Skinny]

Would just be easier to install a Suburban 40 gallon tank.

The only good way of doing it is to use a dual circuit ball valve so both the supply and return are switched at the same time.

I think you potentially can get into cross fedding on hills as mentioned. A lot of guys run an aux tank in the bed with a gravity feed into the filler on the main tank.

You'd think it would over fill the main tank but it works. No idea how the physics work on that.

 

[Sharecropper]

Thanks everybody for your comments. I have decided to follow Skinny's suggestion and add a manual dual port valve to switch between the two tanks. Groco offers a FV-6-5038 bronze 6-port marine valve which will also switch the return lines. Perfect. I will mount the valve under the cab with the lever through a rubber grommet in the cab floor. GROCO FV-Series Six-Port Fuel Valve | West Marine . I will then add the OEM tank switch to switch the dash gauge. I will post photos and a write up in my rebuild thread over on the CUCV Modification forum . https://www.steelsoldiers.com/threads/kinda-got-carried-away-m1028-rebuild.54469/

 

[Skinny]

Let me know where you mount it. I was under the truck today and there is no real good location. I have the same exact valve.

I'm almost at the point of wanting to mount it under the frame somewhere that is still easy to get at the handle without getting under the truck. That way it's way easier to mount. Plus the valve does have an off position so it's passive anti theft.

I'm at a loss for mounting location

I've decided to do dual saddle tanks. Since I have an M1031 a 16 gallon saddle tank will fit right up in the wheel well. Each main 20 gallon saddle will have a 16 probably just gravity fed into it.

Most likely will keep it simple. Ball valve to drain the aux 16 gallon into the main 20 gallon. Then that 3 way valve somewhere on the frame.

Of course I could just scratch all that and use a Burn tank. Decisions Decisions

 

[nyoffroad]

Thanks everybody for your comments. I have decided to follow Skinny's suggestion and add a manual dual port valve to switch between the two tanks. Groco offers a FV-6-5038 bronze 6-port marine valve which will also switch the return lines. Perfect. I will mount the valve under the cab with the lever through a rubber grommet in the cab floor. GROCO FV-Series Six-Port Fuel Valve | West Marine . I will then add the OEM tank switch to switch the dash gauge. I will post photos and a write up in my rebuild thread over on the CUCV Modification forum . https://www.steelsoldiers.com/threads/kinda-got-carried-away-m1028-rebuild.54469/

WOW I haven't seen one of those in 30 years, I'm surprised they're still available. Back in the day that valve would be mounted on the floor between the driver's seat and the door, that way you can just reach down and switch it. If you have bucket seats it might be nice in the center somewhere.

 

[Sharecropper]

Let me know where you mount it. I was under the truck today and there is no real good location. I have the same exact valve.

I'm almost at the point of wanting to mount it under the frame somewhere that is still easy to get at the handle without getting under the truck. That way it's way easier to mount. Plus the valve does have an off position so it's passive anti theft.

I'm at a loss for mounting location

I've decided to do dual saddle tanks. Since I have an M1031 a 16 gallon saddle tank will fit right up in the wheel well. Each main 20 gallon saddle will have a 16 probably just gravity fed into it.

Most likely will keep it simple. Ball valve to drain the aux 16 gallon into the main 20 gallon. Then that 3 way valve somewhere on the frame.

Of course I could just scratch all that and use a Burn tank. Decisions Decisions

Skinny - I got my saddle tanks mounted and the manual valve in place and plumbed. You can see how I did it here https://www.steelsoldiers.com/threads/kinda-got-carried-away-m1028-rebuild.54469/post-2426941

 

[Skinny]

Nice

I have to see if I can mount mine there. I think the generator crossmember is in that spot.