dizzel

Hey all 1st time post in this section. I need some advice running the fuel lines to the engine. Project is in my sig

The MoHo ( *****) has 2 tanks and only one has a guage. I want to use both tanks but they don't have return lines. the old way of switching tanks when it runs out won't work here being a diesel.
So...
I want to pull fuel from one tank and return it to the other and then join the 2 tanks via a gravity line at the bottom. this eliminates the one guage problem.

However I am a little concerned with 2 things
1 The input line is 5/16 and that's what I want to run as a return line, but what about the crossover line?
2 Can I run the return line into the bottom of the second tank or do I have to run it to the top?

I got it running today so I'm happy about that but it's just off a jerry can so...
Thanks

cLAYH

How about an electrc pump that pumps the auxillary tank over to the main tank? When the main tank gets empty(or close to) flip a switch and pump the aux. tank into the main tank. You'd have to remember to switch off the pump when its done pumping though.

apwatson50

I can answer one question, you definitely don't want to return to the bottom, it will create a big restriction and will probably create too much pressure somewhere and overheat the pump.

dizzel

Yeah I figured as much...
Well that still leaves 2 questions..
1. How do I safely drill and tap a hole into the upper portion of the tank because there is no bung up there
2 Will 5/16 hose be enough for the crossover line.

Any Ideas?

Darryl&Rita

A switching valve off a fuel injected vehicle will have two seperate lines, switched between the two tanks. Even gassers have a return line. It should also switch contacts for fuel gauge

cLAYH

Maybe a Vulcan Draw straw kit would do the trick......

cLAYH

At work on the big trucks with dual tanks there is a crossover line joining the bottom of the two tanks. The the fuel draws and returns from one tank but the crossover line equalizes the level between the two tanks and the tanks drain equally. Is this what you are wanting to do?

If so you need a fairly large line connecting them(more like a pipe). Otherwise it will take forever to fill with fuel with at the pumps. Basically the crossover line would need to be near equal to the line on the fuel pump. Otherwise you could fill one tank and the other would only be partially filled and then half an hour down the road they would finally equalize.

However if you had a separate filler for each tank you could fill one tank then the other and you would be able to do a full fill up without having to wait for the tanks to equalize. In which case the cross over line would only need to be as big as the fuel line feeding the engine. It would still need to connect the bottom of the tanks for it to equalize though.

cLAYH

Ok so in light of my above post here's an answer to your two questions

1) 5/16s would work for a return but would be too small for a feed line. If the is was the orignal line feeding the engine I would use it for a return line and run a new line for the feed line, min 3/8s. Ideally the return line would dump into the top of the tank. The feed line needs to come off the bottom so while you could reuse the 5/16s line for the return you couldn't use the same port on the tank.

2) I would return to the same tank as I was drawing, no need to push more fuel thru the crossover line then needed and it could possibly overpressure the 2nd tank if the crossover tube isn't big enough. Yes it needs to go in the top.

dizzel

ok Gottcha

There is a fill port on each tank so the crossover should work. I see what you mean about overpresurising the second tank because it needs to be able to handle the feed and return flows as the tanks are balancing and returning flow at the same time.

I don't have a return port on the feed tank, only a gage and a feed but I'll check just to make sure.

The second tank has no gage only a port to fill and an outlet line near the bottom.

So in light of this info I'm sure you can see why i want to install a crossover line to symplify the whole job, ie not dropping tanks etc.

What I need to do is check to see if there is in fact a return on the primary tank (with the gage) and if not find a way to safely drill a return hole in or near the top of the second tank.

Any thoughts on drilling that hole if I have to ?

Thanks I appreciate the advice

cLAYH

Not sure why you still want to put the return in the 2nd tank but whatever tank you put it in I see two options.

1) Get a kit like the Vulcan draw straw that comes with the special compression bung fitting thing and install that for a return. Just don't bother using the pickup just the fitting. I think for this kit you need to get a hand inside the tank, its intended for the tank in a dodge truck so you can remove the fuel pump canister and stick a hand in.

2) Usually on the filler tube neck there is a 2nd smaller hose running from the top of the tank to the top of the filler neck. You might be able to "T" into this line for your return.

Do both tanks have a fitting on the bottom that you can use for a crossover? If not this will be the hard part.

How were the tanks originally plumbed?

dizzel

both tanks do have a fitting on the bottom for a crossover

Originally the main tank has a gage and 1 feed outlet (I checked) It has a bung at the bottom to drain it (crossover?)
The aux tank has a lower outlet to feed the motor and a lower outlet to feed a small generator.

Both tanks have their own fill neck but no secondary "burp" line.

The tanks outlets go to a switching valve by the drivers side to switch from the aux to main. My dad used to run the non gage aux tank out then switch quickly to the main to use the gage for the remainder of his fuel.

12valve@heart

Just an off-the-wall idea but how about teeing the bottom outlets together to the feed line so that both tanks feed the motor equally; thus solving the fuel gauge issue since both tanks will draw down equally. As far as the return, if you have to drill a return line hole, how about drilling it in the filler neck and returning the fuel up there?

cLAYH

Drawing off the bottom isn't a good idea as any contaiminets like dirt or water or rust will get drawn into the line. Most tanks have the pickup a 1/2" or so off the bottom so that any crap that settles in the tank stays there.

Returning to the fill tube was something I though of as well and may be the easiset route.

dizzel

I agree I think I will check into returning into the fill neck of the gaged tank and bring a crossover from the other tank.

That would be the easiest to tap and remove anyway...

Thanks alot guys
I'll let you know what I come up with in the next couple days.
best regards

dizzel

ok so I got the engine running off the main tank now and have not had enough time to plumb a crossover yet. I ended up putting the return line 5/16 into my filler neck spill tube. I also ran 3/8 to feed the pump.

Thanks all for the help
Eric