Rallye possible cooling h/g problem?

[Mitch]

Treated myself to a black rallye yesterday! 82k on the clock, has had a cam belt/water pump at 63k 2 years ago, Drove it 150 miles back no issues what so ever, couldn't run any better, sits at about 75-80 degrees? Is this right for one of these? Bit low? Anyway after driving the coolant reservoir hisses, there's a slight bit of pressurising but nothing I would say that was serious..no where near as much as my xud makes when it's hot but that's probably on its way to going pop but it works and that's that. Coolant and oil both very clean, there's probably nothing wrong with it, just me worrying! Sorry for any stupid questions etc but I've only ever owned 1 petrol car, so new to them really! Thanks, Mitch.