The 75 and ZT Owners Club Forums - View Single Post

StewartIngram · 27th September 2019, 20:19

Most of the time, when I fill up with lpg, I do a quick mental calculation to check everything is ok. Every so often I do a more accurate one with the calculator. Lpg is always a full tank (till the pump switches off). From this I get the mpg or pence per mile calculation. The car starts on petrol but automatically switches to gas within 1/2 mile max (cold engine). Having got the mpg figure for gas, I am able to compare the same journey on petrol if I wish - rarely. Again full tank to brim. I have a fairly frequent 220 mile return journey which is good for these calculations.
The speedo is known to be 10% high. I have over the years (over a total of 4 cars) been able to have a pretty accurate calibration, originally done in comparison to calibrated police cars and marked measured distances.
The figures I have quoted are pretty accurate, but in all honesty I'm not trying to score points - just keeping my costs down so these calculations most of the time are as I said mental calculations at the pump, backed up by more accurate ones occasionally.
Basically my calculation is how much fuel to fill the gas tank; with the trip mileage set to zero at each fill (I use that as the fuel gauge) I can see the mileage done on that fill (not forgetting the % error for the calibration).
As far as petrol/lpg comparison, the industry says multi point lpg injectors (ie 6 of them just like on petrol) are as efficient as petrol running. The earlier single point injection had about 15% difference. I converted my 827 Sterling(s) with the earlier type, and agreed with the 15% difference there. When I got the first 75, I put a new multipoint kit on it, about 12 years ago. I agree that there is no noticeable difference with the new one, with the same mpg on either fuel. Having done 20k miles p.a. (until I retired last year) I've certainly seen the savings, and been well aware of my running costs!
But I still maintain the biggest factor is driving habits, that vacuum gauge on the A30 taught me well.

Edit to add:
When I got my latest 75 last December (petrol only then) I thought, what a well presented and looked after car - and it really turned out to be so. But the journey home from Rochester proved expensive, returning something like 25mpg. (Same spec as the old car, same driver & driving habits....). Over the next few weeks I tinkered with it and fitted the lpg. Best I got in that time was 31mpg. Now I've checked it all out - and I repeat it was a good 'un - it have improved to the sort of figures I usually get.
Now explain that to me?

27th September 2019, 20:19	#34
StewartIngram Gets stuck in Rover 75 Connoisseur 2.5 V6 auto Join Date: Jan 2008 Location: Chatteris, Cambridgeshire Posts: 903 Thanks: 320 Thanked 159 Times in 127 Posts	Most of the time, when I fill up with lpg, I do a quick mental calculation to check everything is ok. Every so often I do a more accurate one with the calculator. Lpg is always a full tank (till the pump switches off). From this I get the mpg or pence per mile calculation. The car starts on petrol but automatically switches to gas within 1/2 mile max (cold engine). Having got the mpg figure for gas, I am able to compare the same journey on petrol if I wish - rarely. Again full tank to brim. I have a fairly frequent 220 mile return journey which is good for these calculations. The speedo is known to be 10% high. I have over the years (over a total of 4 cars) been able to have a pretty accurate calibration, originally done in comparison to calibrated police cars and marked measured distances. The figures I have quoted are pretty accurate, but in all honesty I'm not trying to score points - just keeping my costs down so these calculations most of the time are as I said mental calculations at the pump, backed up by more accurate ones occasionally. Basically my calculation is how much fuel to fill the gas tank; with the trip mileage set to zero at each fill (I use that as the fuel gauge) I can see the mileage done on that fill (not forgetting the % error for the calibration). As far as petrol/lpg comparison, the industry says multi point lpg injectors (ie 6 of them just like on petrol) are as efficient as petrol running. The earlier single point injection had about 15% difference. I converted my 827 Sterling(s) with the earlier type, and agreed with the 15% difference there. When I got the first 75, I put a new multipoint kit on it, about 12 years ago. I agree that there is no noticeable difference with the new one, with the same mpg on either fuel. Having done 20k miles p.a. (until I retired last year) I've certainly seen the savings, and been well aware of my running costs! But I still maintain the biggest factor is driving habits, that vacuum gauge on the A30 taught me well. Edit to add: When I got my latest 75 last December (petrol only then) I thought, what a well presented and looked after car - and it really turned out to be so. But the journey home from Rochester proved expensive, returning something like 25mpg. (Same spec as the old car, same driver & driving habits....). Over the next few weeks I tinkered with it and fitted the lpg. Best I got in that time was 31mpg. Now I've checked it all out - and I repeat it was a good 'un - it have improved to the sort of figures I usually get. Now explain that to me? Last edited by StewartIngram; 27th September 2019 at 20:27..