Coolant sender unites do fail from time to time but before taking it out make sure you have enough coolant in the system for the sender to work . Often people will think there car has fixed itself when its running hot and then the temperature gauge goes down to nothing . this just means theres no fluid in the system at the sender . without the fluid there the sender cannot send a temp so it goes to zero. So before replacing the sender make sure your fluid level is up to proper levels. Hope this helps