why does my 97 chevy silverado keep saying that its overheating?

[shut up and train!]

ok itll be fine for like 10 minutes
then itll say check gages
so i do its overheating
a few minutes later it goes back to normal and itll keep doing it randomly
i turn on the heat, and its ice cold air when it says thats its overheating
i bought this truck last week for about 4 grand 77k miles and it seemed fine till now lol
and the service engine soon light is on i also checked the coolant and it was fine...idk what else to do i just build cars and shit i dont know how to troubleshoot em...the book doesnt help
it says to get out the car or itll start on fire. and to check the coolant...did both

 

[atomicrockerdude]

It could be an intermittent problem with a sensor.

Check out any sensors that could be faulty.

If all else fails, smack it around a bit and show it whose boss