I assume you meant XJ8 VDP.
If you are blowing the hose off the black thermostat cover at the center of the engine, you need to stop driving that car and have it investigated. That is overheating, pretty severely if that is happening over and over. The thermostat must be replaced at a minimum, and you should have the water pump removed to inspect the impeller for damage. The cooling fans should also be checked out to verify they are operating correctly, both high and low speeds. If nothing turns up at that point, possible headgasket damage should be investigated.
Good luck!