That will be a sure sign that the Thermostat is either missing or stuck open, allowing water through to the radiator when it shouldnt be.
This is located in the housing at the end of the top hose that comes out of the top corner of the main radiator. It MUST be fitted the correct way round (ie the spring side of it goes INTO the engine block side of housing.
You will need to drain the system partially before changing it and it will cost between £8 - £20 for the thermostat and seal depending where you buy it - Halfords would be a good bet.
Refilling system should be done slowly to avoid introducing airlocks which will lead to overheating.
Steve J
August 2007