LPG convertor freezing

Take it to someone who knows what they are doing with plumbing. The usual cause is that the water flow is not sufficient. Installers usually cut into the heater hose and then route back to the sam hose. problem is one heater hose has more pressure than the other. you should identify the high line by momentarily starting the car with the hoses off, one will pump more than the other Put a "Y" piece in the high line to the in of the converter and route the out from the converter to the heater low line joining it with a "T" piece. Some converters also have an adjustment on the top to increase water flow and you should also check for a drain plug on the converter as over time condesation can build up around the diaphram and because it is stagnant it can freeze and cause similar. Just some things for you to check but I had a heavily worked 351 and the converter never froze with these things done.

no - but I don't get out of bed if it's less than 25 degrees :)

It should run better on gas than petrol when cold.
To test water flow (and/or remove air pockets trapped in heater) do the following:
Turn on heater
Remove higher supply hose at convertor
Use garden hose to "backflush" and test if good volume of water is exiting convertor at fitting
Air bubbles coming out of convertor fitting suggest air trapped inside (usually In heater)
Low volume of water exiting convertor usually is a result of restriction in side convertor (rare) or, more than likely, the cheap hose that the gas fitter used in the conversion has swollen on the inside, restricting the flow, or it could have "kinked", thereby retricting flow.
On rare occasions it is the result of a dirty throttle body. (spray pack of cleaner from Repco)

it's not the heater flow, my mechanic checked all that. it's not a cheap gas conversion, about $5k in total. it worked fine today.

what i've noticed is that i got the radiator cleaned out (was 70% blocked) and now it takes a bit longer for the heater to warm up - probably not helping the converter warm up either.

Sorry I can' t give you any technical advice, but I usually start on petrol and run it until the temp guage move up, then switch to LPG

Hycraft auto on snook st Redcliffe / Brisbane the ducks g-ts when it comes to dual fuel systems,