96 tacoma heat problems

So I've been trying to figure out this heating issue out, the heater will take a long time to get warm and then goes cold for a little bit then back to hot, engine temp gauge goes all the way up to hot and kinda hovers there till I turn the truck off, thought the thermostat was bad but I dunno if it can make the heat go from cold to hot back to cold again

 

Bad head gasket/cracked head. Im assuming youve made sure youre not low on coolant.

 

Water pump? If it's cold while at idle, and hot while going. possibly.

 

Yea I checked the coolant and it was all fine, yea it's cold at idle, but 30 of idling it's right near the hot line

 

Head then. Take off your radiator cap while its running, look for bubbles or lots of turbulence.

 

Yes, it can do that. A sticky thermostat, or one that is bad and opening late will cause this condition. A simple enough test to see if the engine has a blown head gasket, or major damage is simply to remove the thermostat completely. Refill the engine and run it. If the temp is good, and you can drive it around and it never gets above say the half way mark, then your thermostat was bad. If the engine still gets hot, inspect your water pump and check for head gasket problems.

 

Ok I will do that, is the thermostat at the end of the upper hose or the lower hose?

 

Upper

 

The thermostat is at the engine block, behind the alternator. where the lower hose goes.