Either the water pump is unable to pump the warmed water into the heater core, or as you suspect, the thermostat may be sticking open. Do you have a temperature gauge or is it just a light that tells you when you're overheated? If it's a gauge, you should be able to tell when the engine is warm. If the temperature is much over 100 degrees F, you should be able to get heat out of the heater core. I'd be real suspicious of the water pump or possibly low coolant level.
If you have a 3.5L most likely the timing belt broke..need more information....
time to get a watch! :)
Coolant level low? Check when cold Cooling fan not working? Thermostat not opening? Dirty or clogged radiator? Bad radiator Cap? Water pump bad?
you have to remove the drl module that located in the fuse box...
Check behind the power steering pump, you will find a plastic housing with the lower rad hose hooked to it as well as the steel tube running to the back of the engine feeding the heater. I think there is 3 10mm bolts holding this housing on.
For a 2.4 litre engine, where the pressure cap is that is the thermostat housing..if you try to remove the pressure cap (in cold temperature only) you will see the thermostat..A damaged thermostat can be diagnosed when an engine running is at above normal temperature by squeezing the radiator hose connected to the thermostat housing..if there is no coolant running in it the thermostat is close then replace it.
check your thermostat and if its opening up then you have a blown head gasket
Could be your thermostat isn't satisfied, caused by where is your thermostat located. It should be away from doors windows in the main room of your house.
The thermostat is located inside the housing on the right side of the engine. There is about as big as a woman's wrist running from the radiator to the engine on the right. It connects to the housing in question. There is generally a bolt on the top and nut on the bottom of this housing that will needs to be removed. Inside lies the thermostat.
have you checked the fan
on a 1993 4.9 it is just to the left of the thermostat where the radiator hose and heater core hoses go into the thermostat it has a couple of wires running into it.
That depends on the thermostat. If it's a 185 thermostat, the engine should run at 185. If it's running too hot, check the thermostat, radiator and water pump. If it's running too cold, replace the thermostat.