Coolant issue

[Lynx O'Grady]

Hello, so i'm having an issue with the cooling on my ranger. (2.3L four banger) I never noticed this when I drove it before buying it, but now that i've had it for a few weeks, i've noticed the temp gauge drop to completely cold.

What'll happen is, I'll be out driving around and the gauge registers that the engine's warm (need is mid-way between hot n' cold) Now when i come to a stop, the gauge will drop to cold, or completely drop to the bottom and stay there until i accelerate from the stop.

Immediately after buying it, i replaced the thermostat housing (it was shot....) the thermostat itself and the sensor thats on the housing. I also replaced the water pump shortly after. After doing all of this, the gauge will still drop at low engine speeds and come back up at high engine speeds. The coolant isnt going anywhere (my oil isnt mocha surprise) and the pump is new, so it should be working fine. Im also concerned since the heat in the cab will blow cold once the gauge drops off to cold too. Im a little bit stumped unless the 2nd coolant sensor is also bad and giving bad readings.

Is there something im overlooking? plugged heater core maybe?

 

[bjurke]

sounds like you are low on antifreeze or you have a air pocket in cooling system. if levels seem fine disconnect heater hose by heater core and add all antifreeze you can there untill full. this assumes rad and overflow reservoir are already full