Possible head gasket replacement

Help!!! I had to leave my son's 2005 Tacoma DC LB Sport at the dealership. The needle is registering hot then cold. How is that possible!!! We have taken very good care of this truck every 5k miles. Is there anyone else with this possible problem. They have not diagnosed it yet.

 

I am doing a head gasket on my cousin's 05 4 runner 1gr right now... very slow coolant leak, engine runs rough when 1st started after sitting overnight, and block tester tested positive for exhaust gas in coolant..

I ran out of time today, but hope to have the heads off Monday, if I have time to work on it again...

 

You failed to mention the mileage or year of the truck. Those would be needed for us to make an opinion on the possibility of it. I just replaced the head gasket on my sons 94 Toyota 4x4 with the 22RE. expensive repair. In his case the truck would overheat as soon as the thermostat opened and the coolant would come out of the fill cap opening like old faithful. I have never seen a needle go hot to cold though.