My MY21 Defender has about 1300 miles on it, and I manage to get about 19mpg (mostly highway) with light touch on the accelerator as I break the engine in. This is even with a bunch of accessories installed on the vehicle – the factory winch, bull bar, Lucky8 rock sliders, rooftop tent, awning etc. Basically, even with all the extra weight, I'm getting decent mpg for this vehicle.

However, I like to take long road trips around the US, and the Defender is going to get a workout this summer, with some days potentially driving in excess of 600 miles. I used to do these trips in my MINI Cooper, which not only gets 35mpg, but has a surprisingly large tank (13 gallon) for its size. In the Defender my range between fill-ups is noticeably shorter, and this is making me curious about installing a larger long-range fuel tank or secondary fuel tank.

Does anyone know of such a tank that can fit the Defender? Any chance that JLR will make one? My friend in Australia says that long-range tanks are a common option for SUVs, so I wonder if JLR already made something for the Australian market that could be imported?

 

I’m putting one or two 4 gallon rotopax’s on the roof just to buy me a safety margin on long trips with the trailer. Even in the western US, this should be plenty to get just about anywhere between gas stations.

 

P300 or p400? I have a p300 and when I starting installing an aux battery, etc. under the rear floor, my first thought was that a large aux fuel tank could be put in that space. Also on the p300 there is a blank hole just beside the fuel filler cap. I assume that is for DEF or PHEV plug? But when I saw that and the space under the rear floor I did consider trying an aux tank install. But the limited cargo space in the back meant I needed that under floor area for other things.

 

So what is the typical range you get on a tank full and what is the tank capacity for that matter?

 

@Tartan I had a similar thought regarding Rotopax. I already picked up a 3-gallon to go on the driver side of the car in the opposite spot from the JLR gear carrier (AKA lunch box). Waiting for either powerfuluk or Lucky8 to release their mounts for it. Can't mount on the roof because I already have a rooftop tent and shovel fully occupying the roof rack, and don't want any more weight up high either.

Rotopax is definitely a solution for an emergency, however, I was thinking more about convenience (less frequent fill-ups), and being able to go out for longer on more remote trails before having to backtrack to a gas station. Just to be clear, I plan to use my Defender a lot off-road and in the backcountry out in the western US. You also get much worse mpg when off-road in low-range traveling at low speeds. Ultimately I'd love to have a bigger fuel tank and a range of 500+ miles.

 

@zac431 I have a P400 SE, 5 seater. I also have a large space under the rear floor. I agree that could be used for a fuel tank, but I currently store all my recovery gear and tools in there, which is very convenient. I suppose something will have to give. I'm interested to know if anyone has already put in a larger fuel tank, or secondary tank, and if it was custom or an official JLR option in another market.

Regarding the blank hole beside the fuel filler cap - I don't believe my vehicle has that.

 

@TheMoke I believe a full tank on the P400 has 23.8 usable gallons according to JLR. I rarely go below 20% left in the tank before filling up again.

As for how far that gets me (range), it really depends. With light use of the accelerator, and coasting on the highway, I get about 10-12mpg city, 22mpg highway. My average mpg on the vehicle so far (1300 miles on the odometer) is 19.8mpg. So realistically, if I drove similar to how I have the first 1300 miles, a full tank could probably last me 450 miles until I was running on fumes. However, I just completed some off-road training classes and plan to take the vehicle off-road this summer on trails and camping for an extended period in the western US. In my (admittedly limited) experience off-road with the Defender, I noticed that the vehicle gets closer to 3-5mpg when in low-range traveling at low speed on uneven ground. So a 24 gallon tank won't get you nearly as far as if you were on blacktop. Perhaps 70 mile range in the worst case.

My point is that I can already see scenarios for me where more fuel would be useful to avoid having to exit the backcountry to get to a gas station. If you're always driving on the road in the US, I don't think there's any problem with the standard fuel tank - you're never very far from a gas station. However, my usage of the vehicle is going to be quite atypical and I expect to be off-the-grid for up to 7 days at a time.

 

I think it would be the rare trail out West where you’ll be doing 70 miles or more in lo range at rock crawling speeds, but if you do that, more power to you. Rim Rocker for instance is mostly done in hi range, and is well within range of a normal tank. I would go crazy rock crawling for 70 miles anyway. Not fun after that long. Most trails I’ve scoped out or done involve long stretches of dirt road where you’d be running hi-range, with occasional rock crawling over relatively short distances. Australian Outback would be a different story, but even there it’s lots of dirt roads in Hi from what I can tell.

 

The Golden Spike trail at Moab is the longest trail and I think it's only 13 miles. Driving from St. George Utah up i-70 to Moab is 60-80 miles of no services but that is in normal transmission usage. Death Valley has some long stretches as well that Rotopaxes would do well with. Steven Firth in Canada is on YouTube and Facebook defender groups and has done the crazy long lonely Yukon Alaska highway thing I forgot the actual name of. Rotopax is our safest option for now. You could probably get 5-8 Rotopax on the roof no problems.

 

@Tartan you make some good points. Maybe I'll never need that extra capacity. However, I'm still interested in finding out if a long range fuel tank is a possibility.