If I remember, when we did the MacMillan 4x4 challenge I topped off gas and fuel tanks where we started in Hereford.

We then did just short of 1000 miles in two days. I emptied the gas tank, then ran on petrol. I remember filling the petrol tank again in the middle of South Wales somewhere then finding gas on the way up to Warrington for the finish. I then topped off on gas again before the short run back home to Macclesfield.

Didn't think that was too bad considering that a lot of those miles were spent blasting around Welsh forests in a blizzard!

I've brimmed mine a couple of times before - when Tesco did their 'clubcard fuel save' or whatever they called it, and I had a couple of 10p/L off discounts to use...

In theory, it's about a 20 gallon tank... assuming an average of say 15mpg (I did get mine up to 22mpg on the dash, on petrol, on the motorway, with the new engine!) then that should give about 300 miles. If you could actually achieve say 20mpg (non stop motorway run maybe?) then that would put 400miles from a 20 gallon tank... so I'd conservatively say that you would be wanting to fill up from about 300-320 if it was brimmed and you weren't doing a solid motorway cruise!

My last LPG fill was 68L and I managed about 180/190 miles from it - giving me about 13.3mpg on gas (think it's tuned a bit rich at the moment!) and I was sitting in London traffic stop/start for about 2 hours, which won't have helped matters!

My trip computer says 19.4mpg (long term average over at least 7 tanks) and when I've manually calculated it it has been accurate to about 0.5mpg.

That's on a daily 26 mile commute (mix of 60 and 70mph roads) each way with a couple of short distance local trips each day.

So on a 20 gallon tank, you should be able to squeeze just 388 miles out of it... not that I'd want to run it dry! 350 is probably a good maximum to go with!

On the blue one, when I was having problems with the gas fill, I did around 700 combined miles mixed, biased towards motorways, driving to empty on LPG and red light on petrol.