Hi, I wonder if anyone out there has encountered a similar problem to mine with a 1000cc Hi-Jet.As I am driving the water temperature suddenly goes very high although the water does not boil,then the fan cuts in and the gauge shows a running normal situation.After a few minutes,the same thing happens and I find when I stop and check the water level the system has pumped water into the overflow container. I have had a new radiator fitted and a new thermostat but the problem is still there.Can anyone please help with an answer.A mechanic has told me that it cant be the cylinder head because there are no leaks and no oil in the water or water in the oil and although the vehicle is pulling quite a bit of weight with a large electric wheelchair plus my Wife and myself,the litle engine performs quite well regarding pulling power.