If the bottom hose isnt warm mate, then the system still has air in it. I found the MB6 is a pig to bleed. I think I posted up a how to on it, or posted instructions somewhere recently. Took me ages to get the air out of mine. Spudley, deffo change the thermostat first mate, and as above, make sure you really get all the air out the system or the problem will persist. If you get all the air definitely out of it and it still persists, then your mechanic is right, could be the water pump is one the way out. Check your hoses every so often to see if they do the same as vtismill. PS: fill your profiles in guys so we can use names instead of usernames! lol Ta!