LPG 3.9 disco overheating

Hi recently bought a 3.9 lpg disco have run it for about 1000 miles uses a bit of water but never overheated although smell of gas when topping up water, last night did a bit of gentle off roading and we had a boil over, temperature gauge was only showing normal but lots of steam! Don`t think it is the head gasket as no sludge in oil or water.....could it be thermostat and sender or the vaporiser for the gas or any one with any other ideas?

Presume it boiled while running on gas?
Slow running, not much air through rad, they do get warm; should have had two warnings though; first temp guage should have risen, then coolant warning lamp on dash should have started flashing.
Few things off the top of my head would be;
Has the LPG been set up 'lean'...
LPG set up often set up very badly, and that isn't going to help.
Next; if temp warnings didn't occur, sounds like localised boiling; which suggests that the water pump isn't shifting water, which in turn suggests either the waterpump is siezed, lazy of firred up, and or, the thermostat isn't opening.
I'd checl the thermostat first, then look at the water-pump.
Did the electric fans infront of the rad 'kick in'?
If they didn't, again, suggests that the rad itself wasn't hot, so water was boiling in the block without getting there.
Lazy water-pumps and stuck thermostats are common problems....
Dont start fearing the worst.

Thanks for your reply Teflon, have ordered new thermostat so will start there

Whatever you do, don't set the LPG lean. Combustion chamber temperatures are already higher than running on petrol as it is & if the thing overheats you could be looking at a cracked block/slipped liner. Been there, got the T-shirt!

when my HG failed the temp guage stayed exactly at the normal driving position until the hose across the head popped and released the pressure at which point it shot straight into the red within a couple of seconds. The other thing is if the water gets low enough to not be covering the temp sensor then the temp reading on the guage will be lower than the real temp of the water so it might not show the temp rising until it is too late.

A smell of gas in the coolant is pretty conclusive that either gas or burnt gas is being passed into the coolant somewhere.. so check your vaporiser.. they are about 60-80 quid and reasonably easy to change.. the heads are a little more..