Dual Fuel Tanks, Dual Draw/Return EFI Fuel System

[rustnrot]

On the Cobalt GT500 (Corsican clone) project we are going to install two identical sized fuel saddle tanks in the rear engine compartment to get more weight in the back due to the surface drive. The engine being used is fuel injection which requires a return line.

One option is to use a six-port valve that will allow switching suction and return lines between tanks. Groco has a manual valve, IMCO a pricy electric one and Parker has come out with an electric one as well (so new I cannot find pricing or availability on the internet yet).

Option two is to "draw fuel evenly" between tanks and "return fuel evenly". Research has revealed that some Big Rig Trucks have been setup this way for years by having equal length and diameter draw fuel suction lines and utilizing this device for the return line.

Here is some info from the vendor:

Return Flow Splitter:

GT Development’s Return Flow Splitter is used in many of today’s Class 8 vehicles to evenly distribute return flow of fuel to the fuel tanks, eliminating the need for a crossover line.
This innovative product for dual draw, dual return fuel systems was introduced in the early 1990’s, and has been adopted as standard equipment on a variety of vehicles makes. This patented product features identical variable flow openings to control return fuel flow which will, with a properly designed and maintained draw system, provide proper fuel balance in dual tank systems.
Has anyone had any experience with this setup in either a truck or a boat? For those that are interested in installation details with drawings I have attached a .pdf.

[zelatore]

Sounds like a good idea in theory, but I suspect in practice it will provide uneven fuel flow with one tank drawing down faster than the other. It would be difficult to get exactly the same fuel plumbing to both tanks.

My vote would be to use manual valves. I've used them before on saddle tank equipped boats and I like having the ability to manually control the draw and return of the fuel to balance the boat. Or suppose I had water in one tank - I could just use the other. Of course, while a system like this will work for you since you designed it, it will be hard to explain to somebody else and could easily lead to drawing from tank A and returning to tank B when B was already full and overflowing out the vent line.

I hear that's frowned on.

[VetteLT193]

If you use that with a tank crossover line you should be ok. if one tank gets too full the fuel will just transfer by way of gravity. generally a valve is put in on the crossover just in case you need to turn it off.

The down side is a crossover on a boat is not perfect because extra weight on one side tends to make the boat lean before the fuel can transfer. If it were me I'd probably do a crossover on the bottom and one on the top. if you have the room height wise the crossover line will be the first point where the fuel will go Vs. the vent line if one tank gets full.

I do not know the USCG rules on lower crossovers with gas... it's for sure ok with diesel because our 42 ocean had a lower crossover hooked to the rear bottom of the tanks.

[MOP]

Tommy was real nice talking with you and like I said it is not necessary to go to the tanks with the returns, all that does is cause flow problems and the need for multiple valves. T into the feed line just before the and filter, makes life very simple. The other trick we spoke of was using two fuel pumps one for each tank with a double throw dash switch that actuated the selected pump and also switched the fuel sender to a single fuel gauge.

Hope to get an eye ball on you soon!

Phil

[VetteLT193]

two fuel pumps is a really good idea. super simple:yes:

[yeller]

You don't have to use a return line to the tanks. My 04 has no return line so it must be plumbed so the fuel circulates within the lines. I haven't checked the fuel line routing closely to see how it is plumbed though. If you eliminate the return lines you could get away with a much cheaper valve.

[penbroke]

I thought all openings had to be in the top of the tank for marine use...


Frank :confused:

[VetteLT193]

I thought all openings had to be in the top of the tank for marine use...
Frank :confused:


Sec. 183.518 Fuel tank openings.

Each opening into the fuel tank must be at or above the topmost surface of the tank.

I don't know what that means exactly because our Ocean had a crossover mounted to the bottom of the tanks.

I will certainly stress again that they boat always leaned before the crossover did anything and that was a big boat and far less likely to lean with changes in weight.

The reason why I am 100% confident of this is the generator was hooked up to one tank only and that tank always took more fuel during fill up. Boats find the center of gravity on their own so the tanks 'think' they are balanced unless the tanks are really different so the crossover helps but it isn't perfect.

[roadtrip se]

You don't normally even start seeing twin tanks on large performance boats until you are way over 30 feet, like about 35.

I would think that the weight sensitivity in a small boat from port to starboard would make this very tricky, even if the rigging issues are resolved.

Have you exhausted all other rigging tweaks? Maybe just moving the existing tank back in the hull or installing a slightly bigger one further back might accomplish the same thing. This is what Donzi did with the Blackhawk rocker hall. Just an idea....

And, oh BTW, Reggie does all of his saddle tanks from the bottom.

[zelatore]

Wasn't aware of that requirement, and I can tell ya there is a whole crapload of high end boats out there with crossovers from the bottom of the tanks....

Yup. It's pretty common.

The only requirement I knew was they had to be USCG certified hose and they had to have positive shut off valves.

[rustnrot]

This is a bare hull we are rebuilding so can put tanks(s) anywhere we want and we also have to get new tanks(s) at some point.

Are the Big Boats diesel or gas, that might make a difference?

In the end I'm not so sure that instead of two 12 gallon saddles might just go with one 18 gal on the passenger side "balanced" out by the battery and trim pump and whatever else we can think of on the driver side. 18 gals of gas weighs about 108 lbs, tank weighs 10 lbs. I figure a battery weighs 60 lbs and the trim pump weighs what about 10-15 lbs?

So there is "only" a difference of 25 lbs more on the passenger side with nobody in the boat and a FULL tank of gas. Throw a dude in the driver seat and you are now at least 150 lbs to the driver side and toss his wife in as passenger and you are probably about even. So if you are boating with a passenger, have a fuller tank, if you are boating alone, go emptier...

[VetteLT193]

I'd rather have it set up so that it is balanced all the time. If you have it balanced with a full tank you'll go out even then come back dragging one tab.

At least if you put two tanks in and they have a super simple manual valve system you can run out on one tank and back on the other and be pretty even the whole time.

Generally, I'd rather manual than auto anything. You can make the decision based on what you are doing that day.

[HallJ]

Use the system from a C5/C6 corvette. They use a venturi system that equalizes the level in the saddle tanks. I may know where to find one!


Jeff

[rustnrot]

Another option is an electro-mechanical one. As I mentioned IMCO has a 6 port electric valve and so does Parker.

A cheaper version would be to use the Pollack plastic :eek: bodied valve below that is used in pickup trucks to select which tank (not gonna go there).

Or simply get 4 normally closed 12 vdc solenoid valves with brass bodies, one on each draw and return line with a DPDT switch and you can choose which tank you draw from as well as switch the appropriate fuel sender in as well. I gotta believe USCG ones are not hard to find...

[Morgan's Cloud]

Don't want to sound like a dork here , but what FI engine are you using that has a fuel return line ?


I've got two of varying sizes and years and neither has a return line ....

[rustnrot]

Pleasure Craft Marine 5.8L efi.

[yeller]

Am I missing something here? Only thing you don't want to do is 'deadhead' the pump by not allowing fuel to circulate through the pump. As long as you have a return line that connects before the pump you won't have to go to the tank. Then you can get away with a 3 port valve before the pump, instead using a 6 port.

[rustnrot]

Basically that is what Phil called me about doing. In fact it would be easy to reroute back into one of those multi-port screw on filters (you know the ones that look like an oil filter). I, the one to always worry, am a little concerned about the fuel heating up and not getting as cool as it should where dumping back into the main tank insures this.

FWIW, I found one of the Return Splitters for ten bucks, and, for grins, will get two buckets filled with water, a bilge pump, and some hose and have my own little Science Fair project and let you all know how it turns out...

[yeller]

In fact it would be easy to reroute back into one of those multi-port screw on filters (you know the ones that look like an oil filter).
That is what mine does.

[anderstontrisailing]

You can't have a lower balance line between the tanks. I wish you could but the regs prevent it. You also can't have the fuel pump more than 12 inches away from the engine, nor have a pressurized return line. Perhaps some builders do not comply with the laws.

I have no comment on builders compliance-I think perhaps there may be too many laws

Just to fill you in on the law for boat manufacturers

USCG Regs Fuel Systems
Title 33 CFR

Section 183.518 Fuel Tank openings.
"Each opening into the fuel tank must be at or above the topmost surface of the tank"
"Fuel tank openings refer to holes into which fittings may be installed or fuel lines attached. Fuel tank fill,
fuel tank vent, fuel distribution, fuel tank sounding, and fuel level sender fitting accesses are examples of
such openings."

183.556 Plugs and fittings.
"A fuel system must not have a fitting for draining fuel."
"There shall be no fitting or component in the fuel system with the purpose of draining fuel from the
fuel system. Fuel tank drains, valves or plugged tee fittings in fuel lines, and drain or bleed valves at
engine connections are prohibited"

183.566 Fuel pumps: Placement.
"Each fuel pump must be on the engine it serves or within 12 inches of the
engine, unless it is a fuel pump used to transfer fuel between tanks."

I can't remember where but there is also a regulation about pressurized return lines-they are NOT allowed.

[BUIZILLA]

why not run it back to the fuel filter housing?

they are multi-ported..

they even have in-out arrows for the Helen Keller crowd,,