The mechanical workings of my long distance / sub fuel tank.
Posted: 30 Jun 2018 12:29
Hi Guys,
I hope this message / inquiry will find you well.
I did a search on the forum to see if my question has not been asked and answered before, but I couldn't find anything. I hope I am not repeating a subject already covered elsewhere. If I am, apologies- and please just refer me to the right post.
I have a question around the "mechanical workings" of the second tank on my Patrol, that is confusing me- and I hope that someone can explain it to me better.
I have a (top) main tank with the fuel gauge, connected to the filler cap, as with a standard car. This tank also has it's own fuel pump. Capacity equals 80 liters.
I then have a second tank further forward, mounted between the two chassis beams, also with a capacity of 80 liters- and this tank is connected to the main tank, on "gravity feed" I presume. I only have one filler cap, through which both tanks are filled. The second tank sits "lower" than my main tank- and is not equipped with a gauge. It has a small "tick-tick" pump behind the side upholstery panel in the luggage area of the Patrol (right rear panel) activated by a dash mounted switch. When this pump is activated, it sends a stream of petrol to the main tank filler pipe just centimeters below the fuel cap- and this petrol then feeds into the main tank.
There is no "direct feed" from this sub tank to the engine, so the idea I presume, is that the petrol is in effect "pumped over" to the main tank for use, where the fuel availability is then supposed to be "read" again, by the single fuel gauge in the main tank.
My question is now this: A smallish stream of petrol is fed into the main tank for use, while the engine is consuming some of it while driving and the surplus should for all intent and purposes, also be "draining" back to the sub tank again via gravity feed, which can cause the vehicle to "run out of fuel" while still having 60 or 70 liters on board, or does it not work like this?
I presume that, if the little tick-tick pump can pump more fuel per minute than what is draining back to the sub tank as well as what the vehicle is "consuming", that a positive balance of fuel will then be present in the main tank- but is this "achievable"?
Also, for how long can I let the little tick-tick pump run- and won't it burn out if operated say for a period of 4 to 5 hours, while constantly pumping the fuel in a circle?
To me, everything is about reliability while being "out in the sticks" with my family and two grand daughters and I cannot afford to get stuck while on a trip.
For many years now, I have only let the Patrol basically run on the main tank only- and I refill before empty. I do however sometimes let the tick-tick pump run for a while, just to try to circulate some of the "old petrol" in the sub tank but because the Patrol is not used very often, the petrol would of course drain back to the sub tank.
While having just retired,it is now my plan to use the Patrol much more frequent for the purpose I have had it for all these years (towing my ski boat to the coast and Mozambique and my freshwater boat to the Vaal river) and I want to get everything in ship-shape and reliable condition.
Would it be advisable to install a second fuel pump or another tick-tick pump (unconnected- but for easy switch-over when needed) such as what I did with my external main fuel pump- or do these units not usually easily fail?
I will really appreciate some guidance and advice- as well as some further information about the mechanical workings of the system as described.
Thanks and kind regards,
Frans
I hope this message / inquiry will find you well.
I did a search on the forum to see if my question has not been asked and answered before, but I couldn't find anything. I hope I am not repeating a subject already covered elsewhere. If I am, apologies- and please just refer me to the right post.
I have a question around the "mechanical workings" of the second tank on my Patrol, that is confusing me- and I hope that someone can explain it to me better.
I have a (top) main tank with the fuel gauge, connected to the filler cap, as with a standard car. This tank also has it's own fuel pump. Capacity equals 80 liters.
I then have a second tank further forward, mounted between the two chassis beams, also with a capacity of 80 liters- and this tank is connected to the main tank, on "gravity feed" I presume. I only have one filler cap, through which both tanks are filled. The second tank sits "lower" than my main tank- and is not equipped with a gauge. It has a small "tick-tick" pump behind the side upholstery panel in the luggage area of the Patrol (right rear panel) activated by a dash mounted switch. When this pump is activated, it sends a stream of petrol to the main tank filler pipe just centimeters below the fuel cap- and this petrol then feeds into the main tank.
There is no "direct feed" from this sub tank to the engine, so the idea I presume, is that the petrol is in effect "pumped over" to the main tank for use, where the fuel availability is then supposed to be "read" again, by the single fuel gauge in the main tank.
My question is now this: A smallish stream of petrol is fed into the main tank for use, while the engine is consuming some of it while driving and the surplus should for all intent and purposes, also be "draining" back to the sub tank again via gravity feed, which can cause the vehicle to "run out of fuel" while still having 60 or 70 liters on board, or does it not work like this?
I presume that, if the little tick-tick pump can pump more fuel per minute than what is draining back to the sub tank as well as what the vehicle is "consuming", that a positive balance of fuel will then be present in the main tank- but is this "achievable"?
Also, for how long can I let the little tick-tick pump run- and won't it burn out if operated say for a period of 4 to 5 hours, while constantly pumping the fuel in a circle?
To me, everything is about reliability while being "out in the sticks" with my family and two grand daughters and I cannot afford to get stuck while on a trip.
For many years now, I have only let the Patrol basically run on the main tank only- and I refill before empty. I do however sometimes let the tick-tick pump run for a while, just to try to circulate some of the "old petrol" in the sub tank but because the Patrol is not used very often, the petrol would of course drain back to the sub tank.
While having just retired,it is now my plan to use the Patrol much more frequent for the purpose I have had it for all these years (towing my ski boat to the coast and Mozambique and my freshwater boat to the Vaal river) and I want to get everything in ship-shape and reliable condition.
Would it be advisable to install a second fuel pump or another tick-tick pump (unconnected- but for easy switch-over when needed) such as what I did with my external main fuel pump- or do these units not usually easily fail?
I will really appreciate some guidance and advice- as well as some further information about the mechanical workings of the system as described.
Thanks and kind regards,
Frans