Coolant temperature

First and foremost, check your coolant level. Next, when the temperature gets to about 3/4 of the way to maximum, does the coolant fan come on? If it does, it could be that the thermostat is bad and needs replaced.

One is the coolant could be low, another is that the thermostat is failing. Sometimes the thermostat will stick and not open in a timely fashion. Ensure that the vehicle is not losing coolant. If it is, you need to hunt down the source of the loss. A faulty radiator cap can also play havoc with the temp and a system that is corroded will have problems allowing the coolant to flow through the radiator and thus not cool as efficiently as it should.