Had to change the radiator on a 2004 standardk series 1.8. I am a total imbecile when it comes to engines, but I thought it would be relatively straightforward. So changed the radiator fine, put in more coolant - althoughit would only take 2-2.5 litres - and started the engine. The top of the radiator got hot very quickly but the bottom stayed cold with the needle going right up to close to the red. I then revved the engine, the needle started going down and the bottom of the radiator got hot. Took it out for a run and the needle stayed half way until I gave it some welly when the needle went back up to just below red. It then floated between there and half. Left it idling when I got back and the fan started, but the temperature stayed just below the red. I am assuming there's a sticking valve somewhere, but any advice gratefully appreciated. Thanks Phil