What you are after is called Flashlube (several alternatives available now, i've just looked), you can buy the flashlube oil from the usual online sources for around £60 for 5 litres IIRC, average mileage 5 litres should last you over 2 years.

The oil is dispensed directly into the air intake via small pipes just upstream of the gas injectors, you buy a Flashlube kit which comprises of a mounting kit plus bottle with adjustable flow screw and (probably best to get an LPG specialist to do this) drill into the air intake and pipe it up.

2 types of kit, one is vacuum fed, the other electronic obviously slightly more expensive.

I have both, a vacuum system on the MB and an electronic one on the Subaru, the fitter suggested going electronic on the Scooby as being Japanese more susceptible to valve seat recession VSR and to get even flows to all cylinders being boxer design, i suspect a good fitter will suggest electronic for you too.

OK, back to your BMW, your engine is pretty well bombproof, and VSR is not a big problem on LPG, nor is it on MB engines (well those that are MB engines and not some Mitsi thing they bought in that need regular timing chain renewals), but good LPG converters like the belt and braces approach leading to long life and happy customers, and some good few years later my old MB runs probably sweeter on gas than it does petrol.

Costs?, maybe £100 will get a standard vacuum kit fitted and £150/£180 an electronic system.

Just out of interest, where is your tank fitted and what sort of mileage to you get please?

further reading www.lpgforum.co.uk/index.php

Edited by gordonbennet on 03/05/2015 at 10:59