*Have you maybe shut off the big tank by mistake & are only using & filling the small tail tank?*
Geoff,
the original tank takes in (or used to) 72-75 litres & the inside tank from 125-130 litres.
it is a 175 litre tank supposed to be,
but i think maybe only actually 150, or the stop is set wrong.
(slightly over the 80% that a LPG tank should take seemed to be what they took, but i never had the big tank empty after it got fitted,
before it was fitted the 90 litre tank with 72 litres did not run dry after a 220 run but i was panicing.)
More will go in on a cold day, (winter time)
& you can run it for say 100 miles from a morning fill
& on a hot afternoon when the Liquid Petroleum has warmed a little & the gas has expanded & find you still can not get more in if you wanted to top it up..
so with 195 litres minimum on board & 2 miles to the litres =390 miles range min.
2.5 miles to the litres = 480 min.
3 miles to the litre = 585 min.
I have done 650 miles on gas without it hicupping.
george
PS Asda credit card at Asda stations gives 1 pence a litre off what is already probably the cheapest LPG other than Kilmarknock BP's LPG (if a regular user). 150 litres saving an extra ?1.50 seems good to me.
www.petrolprices.com