my car gets hot really fast it goes up to about 250 and almost 260 sometimes when i put the heat on it goes back down to 220. And sometimes it doesn't. I had a mechanic take a look at it and he said he thinks its the temp sensor or the gauge is reading wrong. Is the temp sensor gauge the one in the cylinder head on the drivers side ?? How much are they ??

 

does this happen during the highway or traffic?

is your air dam intact?
what coolant mixture are you running? all air out of the system?
fan(s) working?
what t-stat u running?

yes the temp guage sender is in the drivers side head, around the 1 and 3 cyclinders.