No heat and fluctuating engine temp

I am having a problem with a 1996 Ford Taurus station wagon. Basically
the 2 problems are #1 I am getting no heat and #2 the engine temperature gauge is fluctuating.
In my reading people have suggested a number of things which I was going to try including filling the coolant, replacing the thermostat and potentially replacing the radiator cap. Do these fixes sounds reasonable, where is a good place to buy the thermostat and radiator cap (local auto store), and are there any other good possibilities that
might be leading to these problems?
Additionally, if you can point me to how to replace the thermostat or about how much I should be paying for it that would be great.
Thanks in advance!
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snipped-for-privacy@gmail.com wrote:

The thermostat and radiator cap are a good place to start. They are wear items that "should" have been replaced at least once since this car was new. They can be had at any auto parts store and will cost ~$30 US including new coolant. Even if this is not the main cause of the problem, these parts need to be in known proper working order before proceeding. The thermostat is located on the engine, under the housing that the upper radiator hose connects to. 2-3 small bolts and 1 gasket, just drain the coolant first.
Keep in mind that many Tauri of this vintage were subject to corrosion in the cooling system that caused the water pump impeller to erode away. Brown, muddy looking coolant is a good indicator of this problem. If the thermostat, cap, and new coolant doesn't solve the problem, this will be your next suspect.
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