I have a LPG conversion on my V6 2.5 156.
So far its done 120K miles with the conversion and saved me loads of fuel money. Regadsless of what some others may say, if you are cruising the motorway then who cares what the fuel is, especially if its half the price!
When you want some more fun then press the button and its petrol again
Some good things about LPG:
1) Cheap - excluding the installation cost its works out between half and 2/3 the cost of running on petrol (you get less MPG on LPG as its got a lower calorific value).
2) you can drive with a lead right foot with no concerns
3) Kinder to the engine - no carbon deposits silting up your oil and absolutely no 'pinking' ever. (very high octane)
1) If you don`t get a big enough tank you are for ever filling up
2) power is slightly down on petrol but the latest LPG systems make that minimal
1) get the biggest tank you can fit. A 55 litre tank will only actually hold 45 litres. That is good for 200 miles only so you end up filling up a lot. Handy if you have a weak bladder.
2) Shop around for fitters but make sure you get a good kit fitted proffessionaly. Multi-point injection ONLY - I have a 2nd generation kit but you should be getting a 3rd generation as they are much better. Apparently you can hardly notice the difference. Its the single point injection systems that will blow out your air intake system (as MikeM, above)
3) You can`t use the chunnel (yes, really, they think its a bomb)
4) expect to pay up to £2,000 depending on the make of the kit. The Italien and french stuff is best.
You have to do serious miles to make it pay. It took me nearly 2 years to pay of the installation in savings but now I`m rolling in cheap driving and I love not worrying about the fuel bills. My accelerator is either on or off, nothing in between, so I get to hear that lovely V6 acceleration sound all of the time