Hi, some cooling system designs have a single outlet from the expansion tank and on these the tank takes a while to get warm because there isn't any flow of warm coolant through it. Other designs have more than one pipe connected to the tank. For example some have a small pipe from near the top of the radiator that connects to the expansion tank so that any air in the radiator will bleed out automatically. So just check how many pipes are connected to the tank - if there's only one connection the tank will tend to stay cool, although it will get warm eventually due to conduction. Regards Clive