Plastic diesel tanks - venting?

You need a system that lets air in and out but blocks fuel. So do I.

I have a 120 litre extra tank under the ute's canopy. The breather outlet is at the top of the front wall of the tank, extended with a hose and a breather fitting to the filler area, maybe 300-400mm above the tank, to the front wall of the tradie canopy. My transfer arrangement is also gravity.

I like to play on the tracks. On steep downhill fuel sloshes forward and up and out the breather, all over the car.

I'll be interested in what people suggest for you.

Russell
You may well have experience in rigging and cranes and CG but a tank mostly full of fuel has inertia which creates forces suddenly uncontrolled when the CG issue becomes reality. That has to be considered. You didn't say what camper or it's height where the tank will be placed. Doing so will enable more accurate responses.
Any breather like you require would need an external sump vent similar to a Landcruiser has so stop fuel expulsion when expansion or sloshing happens. They are in near the filler system. It has a 0.038% size increase from around 0C to 38C . A poly tank GROWS when initially filled as the hydrocarbon fuel impregnates the tank poly. Around 2% growth from new to used so framing must allow for it to grow in all directions. Can you use an under camper tank? I used a metal tank of 60 litres with integral electric pump from a car under my Tvan. It was great to have when towing. Now poly tanks in cars, mostly fairly flat. would have their own tank pump and ARE reliable and allows a simple 12v connection to pump out through a hose. Much cheaper than $500 from wreckers I reckon and helping environment through reuse. Tank therefore lowering CG too.
I would not fit a tank up high as they are unprotected in event of accident, rollover etc and any leak from any source is still a problem..
Not sure what direction you are pointed in but an open mind to practicality is a good move.

The simple solution is an all-metal tank under the 200 series, fitted up where the spare was and the spare up on the top.
After all the extra fuel is what you hope to need long before a spare wheel.

zz

Just thinking out loud.
If there was a separate smaller tank mounted near the "problem" tank and both tanks connected together with a heavy duty fuel hose , the hose end to the small "overflow tank" would connect to a pipe that was fitted through the wall to the inside and bent towards the bottom , but not touching, this tank would need to have a breather cap, maybe a fuel cap from another vehicle, when the fuel began to expand in the larger tank it would overflow through the hose into the small tank and when the temperature lowered the tank would contract and suck the fuel back from the small tank. Simples LOL
Would this work ? I dunno.
Scrubby.

I don’t see the need for a breather, you don’t have a breather on Jerry cans and his is just a big Jerry can isn’t it.

All I would do is crack the filler cap when you are gravity feeding your main tank to allow it to drain
My mate had this setup on some extended trips we did and it worked just fine

Hi Russell,

You are looking at about 85kgs plus the weight of the tank going on top of your camper trailer. How are you going to lift the roof of your camper trailer with this extra weight on it? A 200 Series spare wheel and tyre would weigh less than half that. Does your LC have a roof rack? Would it be better to put the spare wheel on the roof of the LC, then you could fit a long range fuel tank without having to put a rear wheel carrier on the car.

Macca.

Ok people, let me clarify a few things here; My camper is a home made affair. It's on an 8 x 5 base and I have used coolroom panels (35mm thick) to make what is essentially a bed in a box with a small kitchen / storage area at the rear. The box is about 1500 wide and 1200 high above the chassis so overall height is just over 1.8m. I used 76 x 76 x 3 aluminium angle for joining the panels. It is 100% Sikaflexed and riveted every 140 - 150mm. It's basically bomb proof.

I could hold a dance party on the roof because of it's strength. The trailer empty is 550 kg and has a 1200 GVM, so a payload of 650 kg. I've only used about 200 kg of that with the bed and kitchen gear, plus a small box on the drawbar and the spare tyre. Putting around 110 kg of tank and fuel on the roof will not stress it one little bit. It will raise the c of g but I'm clever enough, like a lot of you, to drive appropriately until I can transfer the fuel to the car. I don't do rock crawling or extreme tracks. I mainly do desert trips. The fuel tank would only be filled when needed for tracks such as the southern part of the Canning Stock Route where you need fuel for 1000 kms. I've already done the CSR with this trailer (and a lot of other long and corrugated tracks) and it was the only vehicle in our group not to suffer any issues at all.

So lets get this clear - I have zero concerns about the extra weight on the roof. I will barely notice it. I am towing with a 200 Series so it hardly feels it. I can also put four 20 litre jerrys on it as well in various places. All up, I could carry 318 litres of fuel if necessary, for the longer desert / soft sand trips.

Putting a tank on the camper roof will save me having to spend nearly $5k for a long range tank and rear wheel carrier for the 200. Actually it would be a lot more than that because a 4t GVM upgrade would then be required as well to keep any sort of useful payload in the 200. And being a gravity fed system, there is zero chance of things going wrong with the transfer process.

So, my only remaining problem is to try and stop diesel leaking out of a breather. It needs to be a short breather so it doesn't get knocked off by branches on the narrower tracks. I'm thinking no more than 300mm above the tank. Or, as I originally said, have no breather.

OK then think of something that has a floating valve in it, at rest it will let air past it and when fluid hits it ,it floats up and blocks the vent
Think scuba breather type of system

Selection of breather fittings available at Whitworths Marine. Tried a link twice & it's not working!

www.whitworths.com.au

Bob

I have some experience with petrol long range tanks in a Range Rover.
Older Range Rover as standard have about a 1litre surge tank inside the RH mudguard.
I had a long range tank high up inside under the window. It took me quite a while to work out how to stop fuel exiting the tank.

The key with any breather is to have the outlet above the tank at all angles.

One technique is to have only a small pinhole restrictor in the breather . This minimises overflow and can/should be accompanied by a "surge tank" again above the fuel at all angles. With sloshing on rough tracks a small amount may exit via the pinhole into the surge tank, then run back as the tank levels.

The surge tank should have an entry for fuel in the bottom ( with a pinhole restrictor somewhere )and an exit at the top with a small filter to catch dust on cooling down.
Whether you are prepared to have a structure above the tank is up to you but that way will work.

Another option might be to use a fuel bladder and run the breather into a hose that bleeds to the ground. I looked at doing the same kind of set up myself for the same sort or reasons as you and that was the best solution I could come up with. I havent progressed any further with the idea but look forward to seeing your solution.

How much does diesel expand? A quick google search reveals the following:
For diesel, the volume expansion coefficient is 9.5 x 10-4 °C-1.
So, for a 100L tank, if the temperature changes by 10°C, then the volume change will be just under one litre.
Hope that helps.

https://www.theboatwarehouse.com.au/motors-parts-inboard-outboard/fuel-breathers/fuel-breather-with-p-trap-fuel-surge-protector/

These are readily available

Option one
A balloon
Not sure there is UV stabilised ones available

Option 2 would be a camel back bladder setup
Where you made a canvas bag up and only have the flex tubing in the sun

Option 3 could be a tyre tube
But would take some fittings to rig something up

There are a few companies the have portable polly diesel tanks that fit in the back of a ute etc find out what they use for a breather would be the easiest solution.

Also as you detest advice fitting it under the camper would be safer because as you mention you can hardly notice you are towing so what's stopping you from tipping it over you may hardly notice till it's to late. It's not the smartest place to put a heavy item especially with your extensive knowledge of raised centre of gravity effects that your not putting into use. Could be a good time to stop venting and maybe listen to others advice as they express their concerns because maybe they actually care .