it is normal to have a bit of pressure but if it blows water out when cold you have a problem i have had loads of issues with the lpg kit and with the coolant and engine i have had to replace the engine as it went 12 months ago to the day check to see if it is the lpg system that is putting pressure in there by turning the gas off at the tank there should be a small valve to it or pull off the connections to the solenoid valve and tape the wires up then run it on gas till it dies so as to run out all the lpg in the system then see if it has pressure once cooled as before hope this helps ya
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p.s i thought you might like to put your own punctuation in. that way you can understand what i was on about in that paragraph!!!!