So hadn’t ever really worked it out but was with a friend just now and he sat and worked out my mpg on lpg (don’t know why) and I found it very low - I’m not talking what the dash says I’m talking facts. We drove 170 mile 164 of it motorway the rest town and used 61litres of gas which translates to 12.7 mpg... is that normal? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

No direct experience but given LPG provides substantially lower MPG than petrol this figure does not surprise me at all since with petrol you’d probably only get 15 or 16 MPG?

Well the trip computer sits on 17.8 so maybe you are right I was wonder if it’s normal or not or if I have an issue Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

I normally get 220 miles from 80 litres with motorway driving

LPG has a 20% lower calorific value so you will use more for the same power output. So to go from 15 /16 mpg down to 12/13 mpg is about right. 2007 Vogue TDV8 in Zermatt Silver with Charcoal

My motorway mpg on lpg is about 16mpg so yes yours is a little low. 2004 Range Rover Vogue 4.4 v8 LPG, Java Black, 22' Hawke Alloys, Black Beast