Dual Tank Fuel Systems "Trucks/Motorhomes"

[Hip]

I have a dual tank setup on my motor home and recently it has issues, vapor locking on a really hot day. it was in the 100's so it was pushing the limits and was towing 4500 ish pounds.

So i want to help this problem by adding a small pusher electric fuel pump back by the tanks but not sure where or how the system switches between tanks?:redneck:

When i switch from Aux to Main not only does the sender wire to the gauge change the source for gauge level it also switches the pump source. How and where?

by searching the lines that i can see... my guess is on top of the aux tank as that is where the feeder line for the filter and suppluy to the Block mounted pump comes from.There appears to be another feeder line from the main tank over to the top of the aux tank also.

Anyone know for sure how this system works both electrically and plumbing wise?

i hate to drop a tank to just find out.

im assuming i could just plum a stand alone 3 psi pusher right before the first filter and be done with it?

 

[Hip]

bump for the dayshift crowd....

 

[crash2]

The ones I have seen hip use a multi pole switch..

 

[Hip]

The ones I have seen hip use a multi pole switch..

so what does that mean? i assume it switches a valve and the sender wire?

i also assume as long as i put the pusher pump after the valve it will work for both tanks?

 

[Hip]

http://www.ebay.com/itm/Universal-F...pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

im assuming there is something like this above the tank.

 

[crash2]

My chev used to use a pull cable to switch the tanks. I went with a gm switching valve and I think it was cheaper than the one you show on Ebay but that was a few years back.

 

[pokey]

I dont know about the switches Hip but my "old" MH had a holley blue pump feeding the mech one on the 454. I dont know if one of those small pumps is going to be enough.

 

[zukkev]

The biggest key to avoiding vapor lock issues is to insulate the fuel lines from the heat as best as possible...alot of times the lines are just hanging out there close to the exhaust, and simply isolating them abit with some sort of shroud or re-routing them away from the exhaust does wonders...

 

[Zoediak]

I just got done dealing with fuel pump replacement in my MH...

I am going to guess that yours does not have any 'in tank' electric pumps...

my motorhome is an '88 with a 460 (ford chassis carbed - single tank)... luckily mine only needs the one in tank pump, but they did offer an aditional 'helper pump' that went inline outside of the tank for the longer rigs...

if this is something like you are trying to do, just place your electric 'helper pump' along the frame rail between the engine and where your fuel line splits to go to the seperate tanks (usually at a valve similar to what was shown).

by placing it there, it will not matter which tank you are running off.


just make sure that any inline pump that you use will supply enough fuel for your existing pump you are trying to 'help'.

also... on another note, after you add a 'helper pump' you could tachnicaly add in a fuel return line for each tank that would be controlled by one of those switches to direct the fuel back to the tank it is drawing from... just make sure the return line is smaller diameter than the supply line.. I have done that many time to help keeping 'vapor locks' away..


sorry for the long boring post... just a couple thoughts...

 

[Hip]

I just got done dealing with fuel pump replacement in my MH...

I am going to guess that yours does not have any 'in tank' electric pumps...

my motorhome is an '88 with a 460 (ford chassis carbed - single tank)... luckily mine only needs the one in tank pump, but they did offer an aditional 'helper pump' that went inline outside of the tank for the longer rigs...

if this is something like you are trying to do, just place your electric 'helper pump' along the frame rail between the engine and where your fuel line splits to go to the seperate tanks (usually at a valve similar to what was shown).

by placing it there, it will not matter which tank you are running off.


just make sure that any inline pump that you use will supply enough fuel for your existing pump you are trying to 'help'.

also... on another note, after you add a 'helper pump' you could tachnicaly add in a fuel return line for each tank that would be controlled by one of those switches to direct the fuel back to the tank it is drawing from... just make sure the return line is smaller diameter than the supply line.. I have done that many time to help keeping 'vapor locks' away..


sorry for the long boring post... just a couple thoughts...

pretty much what i was thinking. most of the 3 to 4 psi pumps only have 1/8 npt inlet and outlet but i found one with 5/16 which is what size line i have existing.

It actually appears to have two return lines built into the block diaphram pump i again "assume they are return lines". they are 1/4" lines smaller than the 5/16 feed line and go to each tank separately?

this one
http://www.summitracing.com/parts/CRT-P60504/

would work but is pricey. anyone know of a cheaper application 4 psi 5/16" inlet/outlet?

 

[Hip]

The biggest key to avoiding vapor lock issues is to insulate the fuel lines from the heat as best as possible...alot of times the lines are just hanging out there close to the exhaust, and simply isolating them abit with some sort of shroud or re-routing them away from the exhaust does wonders...

i looked at that and in this case all the heat just comes from the motor and being incased in the motorhome box. the lines run down the frame and are quite a ways away from exhaust or any heat source.

never had an issue till i tried to drive in tripple digit heat.

 

[zukkev]

Maybe I missed it, but your MH is a P chassis, correct??? BBC fuel supply lines are always 3/8", and the return is usually 5/16"-but I have seen a few with 1/4" returns....depending on the yr.

 

[Zoediak]

pretty much what i was thinking. most of the 3 to 4 psi pumps only have 1/8 npt inlet and outlet but i found one with 5/16 which is what size line i have existing.

It actually appears to have two return lines built into the block diaphram pump i again "assume they are return lines". they are 1/4" lines smaller than the 5/16 feed line and go to each tank separately?

this one
http://www.summitracing.com/parts/CRT-P60504/

would work but is pricey. anyone know of a cheaper application 4 psi 5/16" inlet/outlet?

yeah.. that looks similar to the pump i used on my old 74 CJ.. i used to have masive vapor lock issues when it got hot out. I ran dual tanks on my CJ (one under seat and one in back between rails).

what I did was switch from the mechanical to the electric pump.. i used two of those electric switches (similar to hose anyway)..

i set up relays from a switch on the dash to activate both fuel switches... one was feed from the tanks and the other i hooked up to a return line which was fed from the return line of the inline filter up by the carb...

the dash switch also changed the sender input for the gauge in the dash too.


that got rid of my vapor lock issue when it was all hot and out wheeling.

yeah.. the stupid fuel pump cost a bit.. but in the end it fixed my problem..




the same type of setup "might' work for you too...

i don't have any part numbers or anything, as it was years ago when i did it... and i no longer have that jeep anymore..

but it worked out fairly simple...