Fuel tank musings-LPG NL

[disco stu]

So, I've got NL on LPG, stock petrol tank has been removed and LPG tank is in that gap, with 45l auxiliary petrol tank mounted on passenger side forward of the diff.

I bought a twin LPG tank set up that I was going to try and make fit in the old petrol tank spot, but I'm rethinking things. I'm not sure how long fuel prices will stay at the point they currently are, but when petrol is cheaper than LPG.... My focus is really on increasing range.

I'm thinking that filling the fairly large gap I have with petrol tank would give me a lot more range than the extra 40l LPG tank and be fair bit easier to do.

My questions relate to the best way to do this, and legality in NSW.
Based on VSI 6 I gather fuel tank is considered modification if it doesn't use the original mounting points. Mine would use some of the original mounting points and the others just mount to the floor like the LPG tank is. Anyone know who has to do the inspection on this sort of thing?

I can't seem to see details on construction or other requirements for fuel tanks, anyone know?

For use, I thought using the current tank as the main tank would work best, and just transfer fuel from new to the old when that tank gets low. Anyone got any better ideas?

As a much simpler idea, a few 20l jerry cans meets my requirements nicely and is a lot simpler than faffing around with everything above. but, mounting them somewhere is the issue there. I gather you can't legally mount them on the back of the car. I'm not real keen on them being inside the cabin especially while i'm away. On the roof is an idea also, but I'm keen to avoid having roof cage on the car unless absolutely necessary. Kind of leaves me with little other option, apart from mounting them under the car in the gap there. Don't really like the idea of pulling them out from under there to fill or transfer to the main tank, bringing me back to the permanent mounted tank idea.......

Has anyone any experience with any of this? I guess even experience with inspections on auxiliary fuel tanks would answer some of the questions. Keen to hear other ideas around this also

[erad]

The easiest thing to do would be to dump the LPG bottle and go to a wrecker and get a petrol tank from them. There should be plenty around - who wants them? Plumbing up a return feed from the auxiliary tank should be relatively easy - as part of the petrol tank purchase from the wrecker, you could get a fuel pump and bracket at the same time. Then you would have around 125 L at least of petrol. As for the LPG, sadly I cannot see prices ever coming down again and the number outlets is always going down - soon it will be hard to find an LPG outlet.

[disco stu]

Cheers erad. That's longer term option if lpg is close to petrol prices. Im expecting fuel prices to go back up eventually, and if lpg stays the same I'm thinking it's still worth running. I not long installed lpg injection, before any of this covid issues started, and it should be a lot more efficient than mixer set up from what I've read. With lpg at 90c/l I'm guessing the equivalent cost of petrol at 100-110c/l. Not worth it at the moment

Still haven't got the thing registered. Been slow going with how I've been feeling, but it's pretty much there. No point at the moment though, looks like at least another month or more till I'll be able to go anywhere in it. State forests are closed and I bought this for hunting state forests.

With the second tank though like you're talking about, I'm thinking I would be able to run a relay and just switch between the two tanks pumps and level senders, assuming it comes with those

Anyone know if the diesel tank would suit petrol installation? Local guy is wrecking a diesel, but I wasn't sure if they had the same fuel pump

[erad]

If you have 2 petrol tanks, you really should have a fuel gauge for each tank.Reason is that they should not be allowed to run dry or the petrol pump will burn out (petrol cools the motor). On my NL, I isolated the petrol pump as soon as LPG was selected. This allowed me to go into remote places where LPG was not available and leave the LPG bottle full as a reserve, and then run the petrol tank to empty without worrying about the petrol pump. If this mod was not done, the petrol pump runs all the time. It was a simple mod - I found the power supply to the petrol pump and put a relay in which opened the contacts when LPG was selected.

[disco stu]

I've never liked or understood the fuel pump running while on lpg, for the reason you mention.

Although for my idea, the relay would be open contacts for one tank, and closed contacts for the other. The issue I thought of was plumbing the line to engine-would need to run one way valve in each I figure so it doesn't flow fuel back into the other tank

[erad]

That would work I am sure. It makes me wonder though - the fuel lines are under pressure all the time, even with the engine stopped. There must be a non-return valve somewhere in the system, otherwise the fuel would drain back through the pump when the engine was not running.

Regarding the two fuel gauges etc, I think it would be simpler to have the auxiliary tank as a reserve tank (with a pump) and to pump the petrol back into the main tank manually. You would still need the OEM fuel pump and its mounting bracket, otherwise there is going to be a whopping big hole in the aux tank. If you went with the diesel tank, I am sure that they would be totally different to the petrol tank. For starters, there will be less vent piping etc.

[disco stu]

That's a good point on the fuel lines holding pressure, forgot about that

I've found a few potential options of add in tanks of various dimensions, but unsure of regulations around this. Need to call rms on Monday, but an original tank is much simpler in all aspects.

Might keep an eye out for a tank and just wait and see what fuel prices do

[erad]

Stu:
I don't know where the NRV is on the fuel lines, but there must be one somewhere. I don't think it is in the pump though - maybe it is the fuel pressure regulator?

[disco stu]

I do recall pressure being along the lines in the fuel filter also. I guess depends on the type of pump used for fuel, it could stop back flow due to design. I'll do a bit of a search, distract me from work for even longer!