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#Post#: 82798--------------------------------------------------
Auxiliary fuel tanks
DIR By: pesto
Date: December 23, 2013, 10:15 am
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I've a rear fuel tank mounted to my 109 and want to extend the
fuel capacity.
I have a set of military fuel tanks that were mounted to a
diesel. There is also a fuel change over switch available. How
does such a system work? How much fuel is going back into the
tank by the return line? I'm asking since I see a potential risk
of using the wrong tank which is not connected to the return
line. The non-used tank connected to the return line could start
to spill. Am I wrong?
Are diesel tanks lasting longer? How big is the risk of
leakage/rust by mounting 30 years old tanks?
Last question. How could I solve the issue by having 3 separate
tanks and just one change over switch?
Thanks, Alexander
#Post#: 82935--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: Glen
Date: December 26, 2013, 8:32 pm
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Diesel changeover taps are quite rare, they are very simular to
the petrol tap only they have 2 taps linked together, one for
the supply, the second for the return. The tap eleiments I
belive are the same for each though so you could probubly build
one using two petrol taps if need be. The changeover tap should
also have electrical conections to change the fuel gauge over to
show the running tank. From memory I don't think they have
extra conections for the low fuel warning light, though the tap
I got came from a millitry antispark model so it was a millitry
spec twin tank diesel. The resion I say diesel taps are rare is
because most twin tank landys were millity models (nearly always
petrol) or the large engine petrol models (6/8 cyl models are
far more likely to have factory twin tanks, usally the rear one
+ 1 under seat). I think the same taps were also fitted to
boingys but even the army seems to have given up with twin tanks
thanks to the better economy and larger tanks fitted to them
making range from a single tank acceptable.
If a 30 year old tank still holds liquid thats good enough I
think, quite likely to be rotten though. If its lead coated
steel it might last, the new tanks can rot quite fast, whilst
diesel might protect the metal better watery diesel will
probubly help it rot and may attach some selents or paints that
are okay with petrol. Theres only 1 way to find out.
You can't run 3 tanks with 1 changover switch.
The spillback from the injectors is significant. I had a twin
tank Tdi with no return line and in about 10 minutes of running
on the reserve tank it was nearly empty and my originally empty
tank was then able to be reselected and driven of for a fair bit
more - the fuel gauge had gone up quite a bit. I think if that
tank had been full I would have flooded it.
An alternative is not to have a changeover tap at all, use a
cheep electric fuel pump to pump fuel from your reserve tanks
into the running tank when needed? You should be able to get a
pump that would do this within about 5 minutes at the flick of a
switch, I guess you vould even automate or at least interlock it
with some extra float switches to prevent over filling though if
you were going from the 45 litre tanks to the 68 litre tank then
I'd priobubly just put the pump on a 5...10 min timer relay (ie
rear window relay from a citroen saxo) triggered from a push
button - if you press it when the main tank is low it'll all fit
in the bigger tank and the pump will turn itself off if you
forget to switch it off. All that will probubly cost less than
a second hand changover tap with worn out seals that let diesel
out and air in - neather are good!
#Post#: 82939--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: Arjan
Date: December 27, 2013, 3:26 am
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3 position fuel tap do exist but not in LR's.
I second the electric fuel pump suggestion - we use that on the
1.. (can't say that here)
Very simple - sell the tap + rest to the military guys.
#Post#: 82969--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: pesto
Date: December 27, 2013, 11:26 am
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Thank you for your input!
The tap is a single one and does not work for diesel as I
understand and answeres my question how the return line works. I
think I'm going for a brand new tank and the electric fuel pump
suggestion.
#Post#: 83231--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: abercorn
Date: January 2, 2014, 3:39 pm
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I don't think I have ever seen a diesel 3 way tank switch -
common enough with petrol and I have owned several cars (Series
3 XJ6 etc) with dual tanks. I should imagine that the risk of
getting air into the diesel system makes the switch system
impractical for an oil burner - it doesn't matter with petrol.
The idea of using a Saxo relay to time a leccy pump is an
excellent one.
#Post#: 83235--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: bob86
Date: January 3, 2014, 1:35 am
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Google "Pollack valves" for diesel change over taps.
#Post#: 83241--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: 0jonny0
Date: January 3, 2014, 3:53 am
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I don't know if I am about to sound daft, but I was thinking of
adding a second tank to my diesel under the passenger seat. This
location I assume will be common for most. I was thinking of a
balance pipe??? Is this just daft!
The idea is to link with a suitable diameter pipe so not to get
crudded up. You will fill with one filler, same pipe work, fuel
gauge will work as it will always balance it will just be double
what you previously held.
To stop air locks and ensure flow a breather pipe running across
the top connecting the tanks.
Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
I think a saddle fuel tank on mercs would be similar?
Thoughts welcome.
#Post#: 83242--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: espacekiller
Date: January 3, 2014, 4:03 am
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What if you park facing down a steep hill overnight ??? would it
all drain to the front tank?
#Post#: 83264--------------------------------------------------
Re: Auxiliary fuel tanks
DIR By: abercorn
Date: January 3, 2014, 10:40 am
---------------------------------------------------------
--- Quote from: 0jonny0 link ---
>
> I don't know if I am about to sound daft, but I was thinking
of adding a second tank to my diesel under the passenger seat.
This location I assume will be common for most. I was thinking
of a balance pipe??? Is this just daft!
>
>
> The idea is to link with a suitable diameter pipe so not to
get crudded up. You will fill with one filler, same pipe work,
fuel gauge will work as it will always balance it will just be
double what you previously held.
>
>
> To stop air locks and ensure flow a breather pipe running
across the top connecting the tanks.
>
>
> Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
>
>
> I think a saddle fuel tank on mercs would be similar?
>
>
> Thoughts welcome.
>
--- End Quote ---
--- Quote from: 0jonny0 link ---
>
> I don't know if I am about to sound daft, but I was thinking
of adding a second tank to my diesel under the passenger seat.
This location I assume will be common for most. I was thinking
of a balance pipe??? Is this just daft!
>
>
> The idea is to link with a suitable diameter pipe so not to
get crudded up. You will fill with one filler, same pipe work,
fuel gauge will work as it will always balance it will just be
double what you previously held.
>
>
> To stop air locks and ensure flow a breather pipe running
across the top connecting the tanks.
>
>
> Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
>
>
> I think a saddle fuel tank on mercs would be similar?
>
>
> Thoughts welcome.
>
--- End Quote ---
--- Quote from: 0jonny0 link ---
>
> I don't know if I am about to sound daft, but I was thinking
of adding a second tank to my diesel under the passenger seat.
This location I assume will be common for most. I was thinking
of a balance pipe??? Is this just daft!
>
>
> The idea is to link with a suitable diameter pipe so not to
get crudded up. You will fill with one filler, same pipe work,
fuel gauge will work as it will always balance it will just be
double what you previously held.
>
>
> To stop air locks and ensure flow a breather pipe running
across the top connecting the tanks.
>
>
> Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
>
>
> I think a saddle fuel tank on mercs would be similar?
>
>
> Thoughts welcome.
>
--- End Quote ---
--- Quote from: 0jonny0 link ---
>
> I don't know if I am about to sound daft, but I was thinking
of adding a second tank to my diesel under the passenger seat.
This location I assume will be common for most. I was thinking
of a balance pipe??? Is this just daft!
>
>
> The idea is to link with a suitable diameter pipe so not to
get crudded up. You will fill with one filler, same pipe work,
fuel gauge will work as it will always balance it will just be
double what you previously held.
>
>
> To stop air locks and ensure flow a breather pipe running
across the top connecting the tanks.
>
>
> Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
>
>
> I think a saddle fuel tank on mercs would be similar?
>
>
> Thoughts welcome.
>
--- End Quote ---
--- Quote from: 0jonny0 link ---
>
> I don't know if I am about to sound daft, but I was thinking
of adding a second tank to my diesel under the passenger seat.
This location I assume will be common for most. I was thinking
of a balance pipe??? Is this just daft!
>
>
> The idea is to link with a suitable diameter pipe so not to
get crudded up. You will fill with one filler, same pipe work,
fuel gauge will work as it will always balance it will just be
double what you previously held.
>
>
> To stop air locks and ensure flow a breather pipe running
across the top connecting the tanks.
>
>
> Of course you would have to ensure the pipe cant come off/
damaged but that is no different than damaging the tank.
>
>
> I think a saddle fuel tank on mercs would be similar?
>
>
> Thoughts welcome.
>
--- End Quote ---
I've used a similar solution in the past. The Citroen BX is well
known for it's tiny washer fluid tank. The front washer is
worked from a tank in front of the off side A pillar, the rear
one from a similar sized tank in front of the near side A
pillar. By fitting a balance pipe of a larger diameter than the
pipe that sooks the fluid out you can save many annoying stops
in the rain filling up the front washer bottle.
I can't see any reason why this wouldn't work with gravity fed
tanks provided the balance pipe was of a suitable diameter.
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