Think i have an air lock in my system, but anyway at the weekend I'm going to try and blast my heater matrix clean with the garden hose pipe and then top the system up and bleed. I had a little go last night, not sure if i done it correct though. I took the cap off the cooling water tank, reved car to 3k, next thing eruptions out the water tank, **** myself and turned engine off, then the tank sucked its self clean nearly. Also noticed a screw on the solid pipe that runs accros the top of the engine, i unscrewed this slighlty and water was bubbling out, didnt want to take the screw out incase it was under pressure and blew off everywhere. So, how do i do it?