Thread: Twin tank fuel management

Originally Posted by Robmacca

It will depend on where your filler is, but I can only put a MAX of 65ltrs in and that's with the car facing downhill. My Filler is just infront of the rear wheel but I'd reckon if u tee into the original filler, then u "may" add 3-4ltrs depending on the filler hose ID size....

A la Smoky Yunick? Smoky was found to be using the 4" main frame tubes of his NASCAR as fuel carriers. The regulations specifically listed the dimensions of the fuel tank. Didn't say anything about frame tubes. Smoky hit the roof when taken to task over this. Waving the rule book at officials and asking them to show him where the rules said it couldn't be done. Someone noticed his car was going a good bit longer between pit stops than the competition so the stewards had him drop the fuel tank for measurement. All legal. Smoky put on a fine Smoky of bad temper, called everyone involved mfsob's and other terms of endearment, hopped in the Chevy and drove away. He forgot the fuel tank was still sitting on the pit counter. Oops. "Smoke, you better bring that back here for another look."

He was an amazing bloke! Always pushing the envelope as far as the rules were concerned.
What I would've given to be his understudy for a while!

My car has a 42 l sill tank as the aux tank, it has a land rover fuel level sender in the aux tank that works Ok though the bottom third of the tank goes down quicker than the top part due to the shape of the tank, it slopes up towards the sill for improved ground clearance.( as result the tank will drain down to less than 2 liters)

I ganged together two common 1/4" WOG three way cocks ( or valve), I think they cost about $15 ea at the time.

one cock changes the suctions, the other changes the fuel return to tank
The single lever to operate the two cocks is on the front of the drivers seat base pointing down is the main tank, 90 deg rotation to the right is the aux tank, and the tanks can be changed over on the run.
On the tdi, there is some free space under the drivers seat, the micro switch, valves and piping are mounted in the forward end, so there's still space there to stow stuff.

When the lever is moved to the aux tk position it hits a microswitch, that changes the gauge to the fuel sender in the aux tk.

The two tanks can operate independently of each other. Its simple, reliable, and not expensive to do.

cheers simmo

I have three tanks in a 109, so not identical but broadly comparable to your issue. I'm a firm believer in "if it can go wrong, it will" and "keep it simple".

I have the standard rear tank and the under-seat fill front tanks (no external filler necks as I thought them ugly and I don't want to attract the interest of fuel thieves or Customs officials crossing borders). The front tanks are actually those from UK MoD Series vehicles, but LR also sold these to the civilian market as optional secondary tanks, and even fitted them to the supporting 110s in the last Camel Trophy event. I used the fuel taps from the same vehicles for the feed, with the the return lines having a second, smaller valve mounted in the same cradle as each feed valve and operated by a link to the feed tap's handle. So, the end effect is something similar, though slightly less robust than you "option 2". I actually have two sets of these taps, one to select front or rear, and another selecting between left and right to feed the "front" side of the primary tap. It's simple, cheap and allows me to isolate a tank should I have any reason (different fuel type like vegoil, a leak, weight balancing or whatever). It has proved totally reliable and very easy to use for the last decade. I see no benefit in transfer pumps with electrical or electronic controls at much higher cost and complexity - the wiring, switching and valve actuators will all become vulnerabilities and maintenance issues.

In my 110 I've got 3 tanks (2 sill and 1 LR rear).

I've gone for option 3.

I've had option 1 in a RRC (main tank, sub tank and LPG) and it worked fine.
Ive had option 2 in a Series - the brass stuff eventually leaks and binds.

I selected option 3 because it's simple to fit, simple to replace, and easy to by-pass. I have a 300tdi, so in the event that both facet pumps fail I can just join the pick-up to the aux tank as a bush fix. I know this isn't an option in later models with the pump in the tank. However in later models, should your main tank pump fail, you can use the facet as a pick up pump and get home with a minimum of bush mechanics.