 [ Symptoms ] how to know when cats run fevers [ Disease ] hi if a cat temperature goes up by just 1 degree over its norm its not good for it they can get a bit robotic when walking so with a thermometer do this lubricate the bulb tip with a little petroleum jelly lift the base of the tail and gently slide it into your cat is rectum until half of it is inside keep it in for three minutes withdraw and check the reading you should seek veterinary attention if your cat is temperature is under 99f 37 2c or over 104f 40c hope this helps you good luck