I've been reading up on this a bit having bought an LPG car, & I'm none\nthe wiser. Some say you should always fit an automatic additive adder\nwith LPG even if it's a modern car designed for lead-free petrol, as\nLPG burns much drier & has none of the additives used in unleaded.\n\nOthers say any additives designed to protect valve seats are pure snake\noil, & were just invented to fleece the gullible when leaded petrol\nstarted to disappear.\n\nThe system usually used with LPG is called Flashlube, & is basically a\nScottoiler that dribbles in 1ml of their special fluid for every 1\nlitre of petrol. Needless to say the fluid is hiddeously expensive -\naround 20 quid / litre with postage.\n\nThere's lots of dodgy terms around like 'lubricating the valve seats',\nwhich has led to some people recommending 2-stroke oil or ATF instead.\nThe mind boggles. What there doesn't seem to be are any tests comparing\nidentical cars with & without Flashlube. There are however stories of\npeople stripping their heads after a few hundred miles of Flashlube use\n& finding the valve stems badly coked up.\n\nOn balance, I'm tending towards the snake oil camp, especially as none\nof the manufacturers who offer a bi-fuel option fit Flashlube kits to\nthem afaik.\n\nSo I guess the question is, what are the chances of an aftermarket\nadditive doing anything to protect valve seats, & would it even be\nneeded on a modern engine with hardened seats?