Fellow Disco 1 owners. I have a similar problem with coolant being pushed out of the reservoir cap. I have the upgraded white reservoir. It only does it occasionally when the engine is turned off and only about 250 ml. As soon as you start the engine again it stops pushing coolant out of the cap. The engine runs very smoothly and never over heats and temp is always at normal. There is no white smoke out of the exhaust and no gas bubbles or dirt in the reservoir. Please advise. Thanks.