so tyesterday it's 37 degrees. i'm driving down the road truck is warm at 200. pull up to a stop light and the temp gauge drops and cold air starts cmoing out of the vents. get a green light take off temp gauge jumps back up and hot air starts blowing again. today it's 50 degrees out and i'm driving down the road coming home. temp guage soars to about 210 degrees and stays. i turn on the heater and it holds at 210 till i get home about a half a mile and shut the truck off. 2 questions. does this sound like a bad thermostat to everyone and would this be covered under the engine warranty. any info appreciated.

 

could be

t stat

or

low coolant level


if not sure, replace the stat and drain all the coolant - replace with new.

last thingsI would wonder is:

clogged heater core

malfunctioning water pump

 

checked coolant it is good. will have to think aboug the water pump and heater core. it's only a year old so i hadn't thought about those things.