The mechanical workings of my long distance / sub fuel tank.

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fransvd
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The mechanical workings of my long distance / sub fuel tank.

Post by fransvd » 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

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Peter Connan
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by Peter Connan » 30 Jun 2018 13:52

Firstly, this is obviously not the factory installation. Is your car a Y60? If it is a Y61, it should have room for a second filler inside the cap door. If so, i would change to have seperate fillers, as this does give you more control.

In the Y60, there is only room for one filler cap. This system sounds very similar to my own.
In my car, the hose between the two tanks exits the main tank about half-way up the tank. I would recommend getting under your car and seeing if where the feed comes from on yours, as this is kind-of crucial to understanding how the system will behave, and how to manage it properly.

Assuming it does come from about half-way up, then that means that a sizeable amount of fuel won't drain back to the sub-tank. But it also means that you can only start filling the sub-tank once the main tank has reached that level.

The pump you describe is probably a Facet. They are good quality and are designed as the main pump on many US vehicles. Running it for long periods should be fine, but it must not run dry for more than a few minutes at a time, as petrol is it's lubricant. You will hear it get noisier when it is running dry.
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fransvd
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by fransvd » 30 Jun 2018 16:56

Hi Peter,
Thanks for the reply. It makes perfect sense if the take-off to the sub tank comes from "higher" up in the main tank. I will get under the vehicle and check.
And no, my vehicle is still an old GQ of 1995 which is accident free and still in very good condition, but it has a specially manufactured bell-housing with all Patrol internals, that bolts onto a small block Chevy motor. The extra tank was an after market fitment, to address my high fuel consumption.
I initially had a 383 stroker in it, which I later had replaced with a newly imported Goodwrench "longblock" stock standard Chevy 350 motor. It gives me excellent torque for my heavy towing and beach-work (which I have't gotten around to for years) and works very well. My speedo overreads by close on 20% but if I cruise at true GPS speed of 120 km's per hour (indicated close on 150) my motor runs at 3000 rpm. I then unfortunately get around my towing consumption of just under 5km/l.
Not under load and driving slowish at 100 / 110 true speed, my consumption has been better than 6km/l.
With the above mentioned kind of fuel consumption and planning to now take on longer distance trips at a time, the issues around the long range second tank became something that I just had to get my head around- and I will now fully understand it if the take-off is positioned higher.
Thanks again for your valuable input and kind regards,
Frans.

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Peter Connan
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by Peter Connan » 30 Jun 2018 17:42

Pleasure Frans

You get better consumption than I do. But I'm never putting anything with a Chev badge in my car.

Not even an old T-shirt-convert3d-to-oily-rag...
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fransvd
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by fransvd » 30 Jun 2018 18:06

Lol.
To speak the truth, in general I am very anti-modifications and hybrid "do it yourself" type of vehicles- but I bought this one already converted, quite a few years ago.
I needed the weight and the power for the beach-work and it was already equipped with all the extras which were needed.
I was allowed to test it extensively before I bought it- and it then ticked all the right boxes.
In hindsight, I should have stuck to a stock standard Patrol, like with my other vehicles- and later it just became to expensive to replace it.
I am now going to do some extensive testing of my kit and if I find that everything is too big and heavy, I might downsize to a smaller / lighter ski-boat, that I can tow with a normal double cab like my Isuzu, and take it from there.
As a hoarder, I would not like to get rid of my stuff but maybe it is time to down-size and get equipment that is easier to handle.
The (hopefully near) future will tell.
Kind regards,
Frans.

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Peter Connan
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by Peter Connan » 30 Jun 2018 22:53

Frans, not nocking your choices, but I come from a Ford family...

I have owned several modified cars, and modified several myself, but i must be honest, they have never been more reliable than factory. They may have had other advantages, but improved reliability was never one. And for the stated use, that is perhaps the most important attribute of all.

Having said that, assuming the cooling system is adequate, i can't see how it could be significantly less reliable either.
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fransvd
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by fransvd » 01 Jul 2018 18:06

Hi Peter,
Thanks for your further reply and yes, I concur.
I have an over-sized tropical radiator in, with both a thermal switch as well as an override (to prep for beach or serious up-hill's) and it has served me well.
I had my fare share of irritations like the in-tank pump not working properly or blowing fuses and the vehicle then just dying. I have converted to an external Holly Red pump with an Anderson as back-up and I have not since had any drama. I also had filters blocking (possibly dirt in fuel taken in while in Moz) and I have since removed all inline filters and replaced it with a huge filter, similar to what is used at fuel stations on their petrol pumps. (Tucked away high up on the one chassis beam / leg.)
My electricals started acting up at one stage and I then had new harnesses installed from front to back, which also now seem to function well.
A recent problem encountered, was the light / flicker stalk and the internal "fingers" not having been set correctly. I purchased a new unit every time it packed up and I now already have 3 such units. A clever auto electrician then showed me how he adjusts this, so that problem is now also sorted. (While driving, my lights would sometimes just come on- or some of them- and I thought I had a short. While parked in the garage and opening the roll-up door, the vibration sometimes also set the lights on.)
What I try to do with every challenge or problem encountered, is to do an overkill or repair and then install a sub / replacement unit, added to whatever failed. I.e. I now have the two fuel pumps and I can switch over between the two, by just connecting the fuel line and one power cable which ran to the unit which failed. If the second unit also fails, I will tie a 25 liter container to the roof rack with gravity feed to the carb, just to get home. (I once had to tow my massive Ford F350 double cab 4X4 back from Moz for 1050 km, so I've been there and done that, without any desire to repeat it.)
In the coming weeks I will be testing extensively (after the dyno-tune booked for coming Wednesday to set my peak performance between 2500 and 3000rpm) and I will let you know of my progress.
Kind regards,
Frans.

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Re: The mechanical workings of my long distance / sub fuel tank.

Post by offroadbiker » 02 Jul 2018 09:01

If you need someone to have a look at your fuel system drop me a PM.

Ben from BG auto is used by a couple of people on this forum and he recently installed a second fuel tank to my GQ, works like a charm.

He is in Krugersdorp so should be easy for you to get him to have a look.
Dirk
1996 Nissan Patrol 4.2 ST

fransvd
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Re: The mechanical workings of my long distance / sub fuel tank.

Post by fransvd » 02 Jul 2018 16:55

Thanks Dirk, I'll drop you a PM

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