Fuel Pump By-Pass?

[doug720]

Fuel Pump By-Pass Problem with Aux. Tank

I just finished (Well Almost) installing my 18 gal. aux. fuel tank in my 60. It is a saddle tank mounted inside the frame rail and the drive shaft on the drivers side. I got the tank in AUS. I used a mechanical fuel selector valve and wired a dual switch to allow reading both tanks on the stock dash fuel gauge.

Everything mounted great and it works well except it's now overfilling the stock tank with return fuel from the fuel pump by-pass line. The by-pass allows excess fuel to return to the tank, keeps the carb from flooding and keeps the pressure on the float valve down.

The overfilling occurs when both tanks are full and I'm running on the aux tank first. I know I could run the main stock tank down part way, or even empty first, allowing room in the stock for the returned fuel from the aux tank. But I want to fix the problem so I can use either tank first. I did not plumb a second selector switch for the return line from the pump. I could do this also, more hoses and another valve = more potential issues...but I had an idea.

The manual selector valve I used is plumbed like a "T". The valve has separate "IN's" from each tank and a single supply to the pump. I was thinking of just adding a "T" in the supply line between the tank selector valve outlet and the fuel pump.

Would this work? Would it cause suction issues with pump sucking on it's own return line? I could add a second selector valve, but this would easier and only one valve to change tanks.

You input on this is greatly appreciated.

Thanks,

 

[Randy88FJ62]

More details please! This looks like a great upgrade instead of going after a huge long range tank.

 

[doug720]

I agree,I didn't want to loose my spare under my 60. I don't need or want a big rear bumper in the way of the rear hatch either.

It took a while to find the tank, make the dual fill pipe, etc. The fill pipe allows filling of both tanks from the stock pipe and cap. I added a second pipe off the main fill pipe just below the neck. Put the gas nozzle straight in it fills the stock tank, angle the nozzle to the rear and it fills the aux tank.

I had a custom pipe bent to connect the hose from the tank into the 1/4'r panel. I used marine fuel fill hose and fuel line...both way better then automotive materials.

You have to move the muffler also.

 

[doug720]

No comments on this by-pass into the supply "T" idea?

 

[snowakii]

There should be no problem with the pump
"sucking on its own output" as you say. On some fuel injected vehicles, mostly diesels, there is significant heating of the fuel going through the pump. They need to dump the fuel into the tank and those return lines do get hot. But they are running at much higher pressures than your carbed rig. If there were any significant fuel heating, then you wouldn't want to run the goes-out into the goes-inta.

 

[doug720]

That's what I thought also...It should work. I was questioning if the pump may have a hard time priming or a possible vapor lock issue with a looped fuel pump supply/by-pass line. Or it could damage the pump by sucking on diaphragm? Hopefully not...

I know diesels well, but a carb'd rig with a by-pass fuel line system, I was unsure of. I'm going to give it a quick try today with a simple "T" connection. If all goes well, I'll do a permanent installation.

Thanks,

 

[doug720]

OK, did the temp "T" of the fuel pump by-pass return line into to the fuel pump supply line...and everything appears to be working fine. I can switch tanks back and forth and no fuel overflow from the charcoal canister! Ya!!!

Now, for the permanent connection, I'm moving the "T" as far from the pump as possible, near the selector valve. This should allow plenty of fuel in the loop for pump priming when switching tanks.

Thanks,

 

[Gurr]

Total cost of the project?

 

[FJ40Jim]

OK, did the temp "T" of the fuel pump by-pass return line into to the fuel pump supply line...and everything appears to be working fine.

No, this does not work. When the fuel level gets low the fuel will just recirculate, rather than pulling the low fuel all the way up to the engine. BTDT, caused no end of frustration when climbing hills.

The correct installation uses a universal 6 port fuel selector valve, like this one:
Pollak 6 port tank selector

 

[doug720]

Thanks Jim, you saved me much heartache. I have been running on full fuel tanks so this has not been a problem...YET!

I want to stay with manual valves, so I will just add a second one to
control the return fuel to each tank.

Much appreciated.

Cost to date, tank was $125, me doing all the fab. work and welding, had most of the misc. items on hand, still have to get the Dual filler neck striped and cad plated next week, so around $250-300 total. That does not include exhaust work which I was going to do no matter. These tank have nice heat shields on the exhaust side.

But these tanks are rare in the US. I bought 2 and sold the other here on mud last year. I've seen 2 others on LC's in the US. You can them new in AUS and shipped here for around $1200 - 1400, depending on size, model and options. The kits include everything needed to install but re-routing the exhaust.

Thanks again,

 

[euclid]

My 50 gallon tank tends to overflow if I fill it all the way up on a hot day. The fuel expands a bunch when it warms up compared to the cooler temps in the ground. I just don't fill it all the way up if I know I won't be driving it for a while. Could this be part of the problem on yours?

 

[doug720]

No, mine only happens when engine fuel pump by-pass is pushing fuel back into tank. With another selector valve to control by-pass fuel flow, I should be fine. JimC saved me a lot of trouble in his post above.

In addition, the tank I'm using has a large expansion chamber area to help control the fuel expansion problem.

 

[siddersc]

Would you be able to post up more pictures of how the tank mounts?, I have one that I am about to install so it would help alot with that.
I am just going to install a transfer pump on mine so I can fill the main from the aux tank, I just wanted to keep it a simple as possible.
I think for your set up a 6 port switching valve would work best, but I am sure you will get it working anyway.

 

[siddersc]

Any new info yet?

 

[doug720]

Sorry for the delay, getting ready for vacation next week. I will post some pictures tonight.

I ended up using two selector valves (Eaton # 6747), one for supply and one for return. The valves are mounted on the floor in front of the drivers seat and are easy to change tanks while moving. I had to rework the internal valve position to get the proper orientation of the pointers(drive out a pin and move selector...easy). If I had planned to use 2 valves from the start, the rework would not need to be done. I could of laid out a little more space between them. But Everything works great. I now have right around 50 gals. of fuel on board. I normally get around 12-15 mpg so should have a real range of 450 miles+ worst case, and 5-600 best case.

Driving with both tanks full was no problem at all. I actually feel she rides even better with both tanks full. The central location of the aux. tank is very good for balance. A single rear 50 gal aux. tank is 400 lbs+ mounted past the rear axle. The saddle + stock balances the load a little better IMHO.

The dual filler pipe works perfect and is very easy to use. My installation is a little different than some some. I moved the tank outward towards the frame rails to clear the emergency brake and to have more room around the driveshaft.

I bought the tank and cross bar only, no other install parts, so I had to fabricate the other parts as needed. So I had options.

If you can find one of these tanks...BUY IT! It is proving to be the one of the best mods I have done to my 60.

 

[FJ40Jim]

Doug, do the selector valves also have an off position?
If yes, then you have yourself a cheap anti-theft system also!

 

[doug720]

Jim,

Yes they have an "Off" position. I thought of that to, and even with the markings I doubt many thief's would figure it out.

Double duty is good.

AHHHHH...Tomorrow we start 17 day's in the Eastern Sierra's. It will be good to have plenty of range for exploring.

Doug