Temperature Gauge Query

Hi alll, I recently bought a second-hand '00 Freelander - 1.8 petrol. It appears to have been well looked after and is running well except for two things I've noticed which are troubling me. Firstly, the temperature gauge shoots up to nearly red, stays there for a while, and then drops back to half-way but this only happens intermittently (not every time I drive). I've managed to scare myself silly by looking this up on the net - terrible stories of HGF and blown engines... Secondly, there is sometimes a thump when changing gears. Any ideas on what it could be?

I bought the car from a dealer, who had it fully serviced before I picked it up. I questioned him about the HG before buying it, and asked him if it had ever been replaced, and he claimed that everything was working perfectly.