Cought out by the saddle tanks again

[Head Womble]

Coming back from doing a batch tonight I was just joining the M25 from the M4 when she started to splutter,
luckily I had 40L and my pump in the boot,
so there I was on the hard shoulder pumping fuel in the dark, not the best place to do it believe me.

I had just over 1/4 of a tank, I can normally go just below that in this weather and still be ok.

[Tony]

I never quite understood the mechanics - what is it about the saddle tanks that causes a problem?

I take it that it's almost two tanks linked by a pipe of some kind?

[Head Womble]

Well almost, the tank straddles the propshaft, the fuel takeoff is on one side.
so to make sure both sides drain at the same rate there's a balance pipe that siphones fuel from one side to the other,
to make this worse the fuel is returned on one side and taken from the other.
the 250 also pumps a lot of fuel (most being returned), this is to make priming easier as it doesn't have a priming pump.

No when running veg (or bio in could weather) the balance pipe can't keep up with the flow rate, one pump diesel it's fine.

Take a look at this and you should see what the problem is.
http://www.ebay.co.uk/itm/Mercedes-Benz-C-Class-W203-Genuine-Fuel-Tank-20347028010213752007-/221192425851?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item338018917b

[Tony]

So could you, with a drill, two tank connectors, and a length of pipe, add a supplementary connection between tanks that loops below the propshaft?

[Glycer-rides]

So could you, with a drill, two tank connectors, and a length of pipe, add a supplementary connection between tanks that loops below the propshaft?

I think both Spock and Chissle tried this approach. But it's a bit vulnerable, an underslung link pipe.
Mine did this once in the cold..I put it down to filling up with veg, 'mistakin git for bio'

[julesandtash]

Could you not fit an extra connector to the top of the tank on one side and then modify the return line with a T piece so that it returns to both sides of the tank. That way there would be a more or less equal return to both sides and less of a demand on the balance pipe to equal out the tanks.
Because it would just return to both sides, there would not be any worries about it being underslung and vulnerable.

[Head Womble]

Could you not fit an extra connector to the top of the tank on one side and then modify the return line with a T piece so that it returns to both sides of the tank. That way there would be a more or less equal return to both sides and less of a demand on the balance pipe to equal out the tanks.
Because it would just return to both sides, there would not be any worries about it being underslung and vulnerable.

I have thought about rerouting the return line to the other side of the tank, this way the balance pipe would only need to keep up with 50% of the fuel used.