i have taken the car back to wear i had it converted to LPG, they have informed me that the head-gasket had blown (as it had white smoke coming out of the exhaust). According to them, they have said that the LPG conversion has not caused this. Has anyone else had the same problems?
As TD says, not a conclusive diagnosis for a start. Does the car misfire on both fuels? What other symptoms are present? Water loss? Poor compression? Fumes in expansion tank? They should have checked these...
I think it would be unlikely for them to admit to the possibility that the LPG conversion caused it because they'd know what's coming next.
However, they will have had to re-route parts of the cooling system to heat the evaporator. It's a possibility that they could have caused uneven coolant flow around the head or insufficient bypass flow during warmup. It's possible they didn't bleed the system properly when it was put back together. In addition, if it's running seriously lean on gas this might have contributed.
Problem is, proving any of the above is going to be a challenge. Head gasket failures are not uncommon on the 4 cylinder engines so it may well just be an unfortunate coincidence that it chose now to fail. :-/
.. assuming it has failed..
Kevin