truck wont heat up!

[pbnj22]

My 00 explorer xlt 5.0 AWD will not heat up. The heat in the vehicle works okay but not as great as it used to and even after driving for 20 + minutes the engine temp gauge has barely moved. Is this bad for the truck or is there anything i should check?
the coolant is full and not frozen, could the thermostat be stuck open or broken open?

 

[gonenuke]

Sounds like the thermostat is stuck open. Has this just started or has it been going on for a while?

 

[pbnj22]

Just started, just since it got super cold out like 10 degrees... I just replaced fuel filter, air filter, plugs, and plug wires and cleaned the injectors recently but i couldnt imagine any of these things causing this problem since to me they are unrelated, i will check thermostat tonight after work.

 

[marragtop]

Keep in mind that if the Tstat is sticking open, it can also stick closed which could result in an overheat and signifcant problems. Don't ignore a questionable Tstat.