What's the best way to tie 2 fuel tanks together?

[mongo75]

I am racking my brain trying to figure the best way to tie together 2 gasoline fuel tanks so my one Chrysler 440 can draw from both tanks, AND keep the level of both tanks the same.

I can rig a line that goes to a transfer pump so I can transfer gas as one gets low, but I really would like to keep them equalized. I know in a diesel application, you can actually run a line from the bottom of a tank to the bottom of another tank, but I don't think it'll jive in a gasoline application. RIght now my two tanks are dry and I could drill a hole, and braze brass shut off valve to the bottom, an "hide" it, but my fear is a fitting breaking off and dumping 150 gallos on gas into my bilge. Looking for any ideas!!!!

[marshmat]

Hi Danny,

Why is it so critical that the tank levels be kept equal? A boat big enough to use a Chrysler 440 as primary power should be able to handle a slight imbalance.

The easiest way, probably, would be to just have a separate suction line from each, with a couple of valves so that you can select which tank the engine is drawing from. If you want to keep them balanced, just open one valve and close the other every couple of hours.

Trying to add plumbing to the bottom of the tanks, to make them act as a single tank, doesn't strike me as a particularly beneficial way of doing things- and, as you say, there's the risk of draining all your fuel into the bilge if something gets knocked out of place.

[CDK]

Two suction lines from the top of each tank, brought together at a 4-way valve, (left, right, both and none) the output of the valve connected to the fuel pump.
Once you have drawn fuel from both tanks, turn the valve to "both", switch off the engine and go home. The next time you are on board, you'll see that the fuel level in both tanks is (almost) equal.

You could also just install a T without valve, but then you do not have the advantage of a spare quantity of fuel you can save for an emergency.

[mongo75]

Matt, my boat is a 25' Luhrs flybridge, so it's not all that big, and plus I got a fat friend- so fatty on port side plus empty stbd tank equals excessive roll LOL... They are 75 gal tanks. While it does require more work, you idea does work and I had to do the same on my first boat.

CDK- I like your idea as well, as it seems the valve would create a link across which the fuel would flow to keep level, provided there was a constant suction in the line. Where could I get a 4 way valve? I don't know if I've ever seen one before.

[CDK]

Originally Posted by mongo75

CDK- I like your idea as well, as it seems the valve would create a link across which the fuel would flow to keep level, provided there was a constant suction in the line. Where could I get a 4 way valve? I don't know if I've ever seen one before.

Such valves are used in industrial hydraulics. But you could also use two simple ball valves, one in each suction line. Once the fuel lines are filled, no suction is needed to equal the levels.

What's the problem with tying the tanks together?

[mongo75]

CDK- yeah, being a hydraulic guy on H-1 helicopters, I know what you mean, saw them in school. I kinda like the simplicity (and price) of a ball valve. I could use ball valves at the tank and an anti siphon at the tee. AND if Ireally wanted too I could always plumb in a pump, bt not really necessary.

Mark- per Coast Guard regs, on a gasoline tank, you can not have any fittings below the top of the tank, whereas in a diesel tank, you can have well, just about anything hanging off it you want. Gas is flammable, diesel is combustable- big difference in safety precautions. I wish I could afford a diesel, but nope, I'm just a poor Marine with bills to pay...

[PAR]

You have to "pierce the tanks from above, not side or bottom fittings are permitted, so letting gravity do the work for you isn't possible. Other wise you'd be able to "T" the tanks at the bottom and suck both down at the same time.

You still can do this, though it's not necessary, nor desirable. If you get a bad batch of fuel, you may have one serviceable tank, but not if their are "Siamesed".

If drawing through a single pump you'll need a fuel distribution manifold, their valves, solenoids, switching and some plumbing modifications. Most like to run twin systems, with two pumps and just a distribution manifold.

Yeah, I forgot. Gas.

[Submarine Tom]

I use two ball valves on my gas outboard. I can trim slightly if need be by

selecting one over the other. There is some redundancy should one fail for

whatever reason. It allows one degree of trouble shooting. I feel a tiny bit

better when I leave the boat with both valves "off". Theft, fire...

Tom

[naturewaterboy]

I have two tanks and two outboards. I plan to run a line out of each tank to filters - each tank to it's own filter - but then I'll install T fittings before the filters and put a cross over line with a valve - this will allow me to suck out of both tanks to one filter if needed - also I'm putting a crossover line AFTER the filters and before the engines - with a valve in this line also. I also plan to put valves on both sides of each filter. I also have valves on each tank. I'll have a total of 8 valves, but if I have problems with one tank, or one filter, I'll be able to run either or both engines. If you are interested I'll post a drawing of this setup.