my 1998 chevy silverado engine is not getting hot enough. It started reading about 200 when completely warm and would suddenly drop down to about 150, then climb back up and drop. Now it will not get past 150. I have replaced the thermastat and some of the heater hoses. The heater of course will not work. It does have plenty of antifreeze, and all other fluids are good.

 

sounds like trapped air in the system. no heat from the hvac system can be caused by low coolant levels.