After some minor teething problems at the start, the car has run faultlessly since, and we have also done our bit for the environment because LPG – liquefied petroleum gas – is a much cleaner-burning fuel.
Since our car was converted, Prins has launched its cheaper "Silverline" version aimed at the standard car market that has reduced the basic price to £999 plus VAT – £1,370 in total with something called ValveCare, and, if I were embarking on the project now, I'd go for one of those.
Drivers who do higher mileage, and those who run cars that are fuel inefficient (such as a 4x4) will find that the payback period for switching to LPG could be as little as a year.
It is mystifying that more drivers are not going down the LPG route. Sceptics told us that we would never be able to find LPG, fuel consumption would be poor and reliability iffy. But 12 months on, with 88,000 miles now on the clock, our car has performed perfectly.
Best of all, we've become used to paying £32 to fill our car compared with £70 if we were buying petrol. We paid an average of around 74p a litre for LPG, while the price of petrol has been close to £1.36. Each tank (about 9.6 gallons) gives us around 290 miles. Running costs on gas – we still use a little petrol per tank – have been 12p a mile, compared with 17p if running purely on petrol. The conversion was carried out at Prins in Southampton and took around four days at a price of £1,500. ValveCare cost £150, although that's not necessary on German or Swedish cars. Where our spare tyre once sat there is now a gas tank. We carry a tyre repair gas canister instead. Inside, the only sign of the conversion is a control panel mounted on the dash which shows which fuel you are using, and how much gas is in the tank. You wouldn't know that you are driving a gas-powered car. It starts on petrol and after a mile or so, seamlessly switches. The only sign is the lights changing on the control panel. If you run out of gas, the car automatically switches back to petrol, and, again, you wouldn't know except the system alerts you with a short buzz.
Before the car was converted, it was achieving around 38mpg depending on the journey type. Most converters say you will get 15%-20% fewer miles per gallon because gas has less energy than petrol. Over the year we have got around 29mpg, a reduction of 23%. The biggest disparity is on fast motorway runs. On slower roads and around town, the fuel reduction is closer to 15%.
Our car's variable valve engine appears to suffer a bigger loss than most other LPG users, but the savings have still been substantial.
One thing I have not got used to is the huge disparity in LPG prices. On a recent trip to the West Country, in Bristol it was 65p a litre. A few miles down the road they were charging 78p. Our two nearest garages, five miles apart, charge 73.9p and 83p. In Luxembourg this summer we paid 53p.
The key to making LPG work for you is to locate a cheap local source. Website FillLpg.co.uk is the best I've found as it gives the location of filling stations and a recent price. It can be a pain sometime to detour for a fill-up. But hey, £650 is a good saving.
Other running costs have been small. Most insurers don't load premiums for properly-installed LPG systems, and ours – the Co-operative – was no different.
ValveCare fluid has cost £50 over the year. A service of the system every year at our local Prins agent costs £120 plus VAT, although this can be reduced if the car has its standard service at the same time.
The LPG system in this test was installed and paid for jointly by Prins and Autogas, supplier of LPG fuel.