Thermastat

If the thermostat's not working properly your engine may tend to run hot or even overheat or may tend to seem like it takes a long time to warm up. Either way it's not good to have a faulty thermostat.

Thermostat's are usually replaced as common maintenance items whenver any work is being done to the cooling system.

If you don't recall replacing it before then it'd probably be good idea while you're thinking about it.