overheating galaxy?

i have just bought an n reg 2 litre petrol galaxy, i have noticed the engine is getting burning hot though the temperature reading on the dash is normal, and the water in the expansion tank is not as hot as the top of the engine. is this normal, i have seen 1 garage and they have said yes. also when u take cap of expansion tank when hot the water does not push out, my other car did is this normal aswell , any replies would be gratefull,ta