Temp Guage going up and down 2006 toyota Tacoma 4.0

My 2006 Tacoma 4.0 does fine until I turn the ac on and them after a while it it will overheat then drop and keep doing it. It was dumping Coolant out of the overflow tank. It's not head gasket we've had it checked. Trick has 240k. Thanks

 

For starters, how's the fan clutch - does it get harder to spin the fan when the truck is warmed up? If not, that may be the culprit. Also make sure the serpentine belt is in good condition and has good tension.

 

How did you check the head gasket?

 

Sticky thermostat or low coolant would be other suspect areas aside from a head gasket.

 

I'm thinking thermostat. You are going to have to check your fan clutch for sure though. If all that tests out fine go straight for the head gasket and check that.

 

I agree with the others.

Other than that, I remember 1 person reporting a bad radiator cap causing coolant to over flow from the reservoir.
Apparently it was weak and allowing the coolant in the overflow tank too soon.

Not sure I believe that was the real source of the problem. I never seen the guy post back since. But hopefully for him, it was that simple.

If you are sure it’s not the HG’s. I’d start with the thermostat.