I have a 2008 Ford Fiesta 1.6i. The car heats up and builds pressure in the water bottle that causes the cap to pop open and boiling water to come out. I have taken it to Rord where they have done a pressure test on the block and there's no problems. They have checked the thermostat and no problem there.
So what could be the cause of the water bottle cap popping off?
Please give me some insight on what to do.