1995 Mercury Tracer

Heater problem
1995 Mercury Tracer 4 cyl Two Wheel Drive Automatic 104000 miles

I've thermostat replaced on my 1995 Mercury Tracer (104000 mi) about 2 months ago, now the heater is blowing mild warm air not hot enough, even at the hottest setting. Also noticed that engine temp indicator needle is not at the center, it is alweays staying close the " C" side. Any suggestion?
January 5, 2010.

Heater Core " Plugged

WARNING: The heater core inlet hose will become too hot to handle if the system is working correctly.

Check to see that the engine coolant is at the correct level.
Start the engine and turn on the heater.
When the engine coolant reaches operating temperature, feel the heater core inlet and outlet hose to see if they are hot.
If the inlet hose is not hot: the thermostat is not working correctly.
If the outlet hose is not hot: the heater core may have an air pocket.
The heater core may be restricted or plugged.
If both are hot, the temperature blend door in the heater plenum may be broken or stuck.

Jan 5, 2010.