95 f150. Is overheating at times t(temp gage often fluctuates) and heat is blowing out cold air.

What I did.

Flushed coolant
Replaced thermostat

What is happening.
Now water is not leaving reserve tank.
Truck temp fluctuates.
Not sure thermostat is opening.
Blows cold air when heat is on.

I'm new to trucks please excuse my ignorance if there is any I'm just learning how coolant system works.

Thank you all

 

heater core clogged

 

Thanks. Would it be more beneficial to replace or clean out?

 

It would be better to replace the heater core rather than try to flush it.

 

Okay great. Thank you.

 

Access panel behind the glove box