Long-range fuel and water tanks: what they really cost you
The question people arrive with is how much extra range a long range tank buys them. The better question, and the one that decides whether it's a good idea, is what it costs. Fuel and water are among the heaviest things you'll ever put on a touring vehicle, and unlike a bar or drawers they're a weight you're choosing to carry because it's useful somewhere else.
Do the sum before you shop. Water is one kilogram per litre, near enough. Diesel is a bit over eight tenths of a kilogram per litre depending on temperature and blend, so call it four fifths for planning. A hundred litres of extra fuel and a hundred litres of water is roughly 180 kg of payload, plus the empty weight of the tanks and hardware, before you've packed a swag. On a dual cab already carrying a canopy, drawers and a bar, that's often what tips a build over its GVM.
Extra range is only useful if you can carry it
Additional capacity is a trip weight, not a permanent one — you fill it for the desert crossing and run it near empty the rest of the year. That's a legitimate way to use payload, but your suspension has to cope with both states, and the weighbridge ticket that matters is the one taken with the tanks full.
More range past a point also stops paying. If your longest fuel leg is settled by one particular stretch of road, size the tank for that leg with a sensible reserve and stop. Buying the biggest tank in the catalogue because it was only a little more money is how people carry dead weight for years.
Work out your worst-case leg in kilometres, apply your genuine loaded and towing consumption rather than the brochure figure, and add a reserve for detours, headwinds, soft sand and a closed roadhouse. Then check that capacity against the payload you have left.
Replacement versus auxiliary
A replacement tank takes the factory tank out and puts a larger one in its place. One tank, one filler, one gauge, nothing to switch. It keeps the weight roughly where the vehicle was designed to carry it, which is the best thing about it. The trade-off is that more capacity in the same space usually means a deeper or wider tank, which can cost ground clearance. Ask about fitted depth relative to standard, and whether underbody protection is available or required.
An auxiliary tank adds capacity elsewhere — commonly where a spare wheel or chassis void sits — and leaves the factory tank alone. You keep the original as a known quantity, and you can travel without the extra tank filled. The costs are complexity and location: you need either a transfer pump feeding the main tank or a valve arrangement drawing from one tank at a time, and both can fail a long way from a workshop. Spare wheel relocation is a common consequence, and a spare on a rear bar adds weight of its own.
A replacement tank is simpler and generally better if it fits. An auxiliary suits a vehicle whose layout won't take a bigger main tank. If you go auxiliary, understand the plumbing first: gravity or pump, manual or automatic switching, what happens if it runs when the main tank is full, and how you'd get home if the pump died.
Fitment here is about as series-specific as it gets
A fuel tank has to live around the chassis rails, the crossmembers, the exhaust and its heat shielding, the handbrake and brake lines, the driveshaft, the spare wheel carrier, and — on modern diesels — the emissions hardware, including the diesel exhaust fluid tank and the particulate filter. All of that moves between series, and some of it between cab configurations and wheelbases within one series.
That's why long range tanks are catalogued in more detail than most accessories: series, build date, cab configuration, wheelbase, sometimes drivetrain and emissions specification. A tank listed for one generation frequently has nothing in common with the next.
Check the retailer lists the tank for your series, build date and body configuration, and quote your VIN. A phone call before ordering is worth ten minutes, because freight on a returned tank is not cheap.
The fuel gauge will probably lie to you
The factory sender was calibrated for the shape of the factory tank. Put a differently shaped tank underneath it — and long range tanks are shaped around obstacles, so they're rarely simple boxes — and the relationship between float position and litres remaining changes.
In practice that means a gauge that sits on full for an unreasonably long time then falls quickly through the bottom half, or the reverse. Some tanks come with a matched sender, some use the original, and some auxiliary setups add a second gauge or a light. Ask which you're getting.
The answer is to stop navigating by the gauge. Use the trip meter and a known litres-per-hundred figure, fill to the brim a few times early and record what went in. Do that on a trip where being wrong is inconvenient rather than serious.
Where the weight sits
Fuel and water low and between the axles is the best case — the least disruptive place for a large mass. Weight behind the rear axle behaves like ball weight: it loads the rear, lightens the front, and makes the vehicle less settled on corrugations. Two more points:
- Baffles matter. A partly full tank without internal baffling lets a large mass slosh, which you feel most on side slopes and under braking. Ask whether the tank is baffled.
- A water tank under the tray or chassis is exposed. It picks up heat, road grime and stone strike, and it's the hardest place to inspect. A tank inside a canopy is easier to look after but sits higher and further back.
If you're already close to your limits, more capacity is not the upgrade. Weighing the vehicle is.
Water tanks and the hygiene problem
Water that's sat in a warm tank for three weeks is not the same as water from a tap, and this is the part people ignore until they're unwell in a remote place.
- Use food-grade tanks and potable-rated hose and fittings. Not every plastic tank or clear hose suits drinking water, and non-potable hose taints it badly.
- Light grows algae. Translucent tanks in daylight eventually grow something. Opaque tanks and shaded mounting are better.
- Design so it can be drained and cleaned. A tank with no low drain point and no inspection access accumulates sediment you can't remove. Ask about both before you buy, and sanitise periodically per the manufacturer's instructions.
- Filter at the tap, not just the fill. An inline filter on the outlet is cheap insurance. Carry a way to treat water too, because you'll eventually fill from somewhere questionable.
- Keep drinking water separate from washing water if you carry a lot. You get to be relaxed about one and careful about the other.
- Don't leave it part full for months. Keep it full and turned over, or drain it dry.
Jerry cans, and when they're the better answer
For occasional extra range, jerry cans are cheap, need no fitting, and come off when you don't need them. That flexibility is genuinely valuable.
The catches are that a full can plus its holder is a substantial weight, and it usually ends up somewhere bad — on the roof, the worst possible place, or on a rear bar behind the axle. Cans have to be properly restrained, carrying fuel inside an occupied cabin is a poor idea, and the can needs to be suitable for fuel and in good condition.
If you carry cans more than a couple of times a year, a tank is the better answer. If it's once, cans are fine.
Before you buy
- Work out your remaining payload first, and weigh the vehicle at a public weighbridge as it sits.
- Size the tank for your worst-case leg plus a reserve, not the biggest number available.
- Budget the weight of a full tank — fuel at roughly four fifths of a kilogram per litre, water at one.
- Confirm the retailer lists the tank for your series, build date, cab configuration and wheelbase, and quote your VIN.
- Ask about ground clearance relative to standard, and whether protection is available.
- Ask what happens to your fuel gauge, and whether a matched sender is included.
- For an auxiliary tank, understand the transfer arrangement and what happens when it fails.
- Ask whether the tank is baffled, and where a water tank drains and can be inspected.
- Have fuel system work done by a competent fitter, and ask your state road authority whether the modification has approval or inspection implications.
- Re-weigh the vehicle after fitting, with the tanks full.
This guide is general information, not fitting or engineering advice. Fitment, compliance and safety depend on your specific vehicle — confirm with the retailer and a qualified fitter before you buy.