Thermastat replacement how to replace thermastat on a 2004 christler 300m engine runs cold

MAKE SURE THE TRUCK IS COLD FOLLOW THE RADIATOR HOSE ON THE RIGHT TO THE THERMOSTAT REMOVE THE HOUSING REMOVE OLD ONE CLEAN OLD GASKET AND REPLACE WITH NEW ONE

Depending on Your vehicle engine model, Vin #'s K, M, with a 3.5 ltr engine, the torque spec are 109 in lbs.

If the engine Vin # is a V, then the torque 113 in lbs

Yes, change out the thermostat. It's probably stuck all the way open because in Arizona it rarely gets cold enough for it to need to close down allowing the engine to warm up. It's easy to do. Try this link for instructions.

The first step is to determine whether the engine is actually running cold or if the engine computer just "thinks" it is. Your temperature gauge is controlled by the engine computer. I use an infrared thermometer directed at the base of the Engine Coolant Temp (ECT) sensor while watching the ECT sensor data on the computer to see if they match. This should be done before replacing ANY parts. You need to make sure that the ECT is not "lying" to your engine computer. Your vehicle is also equipped with a Cylinder Head Temperature (CHT) sensor to measure the the temperature at the cylinder head. (The ECT is located in the intake manifold.) These should read within 5 or 6 degrees from each other at all times. If it is determined that the sensors are all functioning properly, and the engine actually is running cold, then I would recommend getting a thermostat from the dealer. (I have had a few problems with aftermarket thermostats.)

check and make shure the fan is cuming on when it should, the coolant could simply be evaperating from the engin getting to hot

you do not give enough info. is the temp gauge showing the engine temperature is normal, about in the middle or a little less. if it reds colder probably the thermastat.either way make sure the radiator itself is full. engine cold remove.remove the cap and fill wait until it settles and refill start the engine and it should go down a little morer ,fillagain put the cap back on and fill the resevoir only to its full mark.see what happens.if this is all ok and the heater hoses are both hot you will have to probably replace the temperature blend door actuator.

Run engine untill warmed up, put your hand on the top radiator hose, is it hot, can you squeeze it ?
If not then change your thermastat.
If that does not help, you may have a bad head gasket.
Please let me know.

Did you run engine from cold, WITH HEATER ON, and fill cap off when re-filling system? If not, try that and see what happens. Let the engine get up to operating temperature and rad fan come on to cool 2 or 3 times before putting cap back on.

Yes the water pump does run of the timing belt system.
Directly from the service manual:

The 3.5L water pump has a die cast aluminum
housing and a plastic swept vane impeller. It bolts
directly to the right rear timing belt cover using an
O-ring for sealing. The water pump is
driven by the engine timing belt.

REMOVAL
The water pump on all models can be replaced
without discharging the air conditioning system.
WARNING: DO NOT REMOVE PRESSURE CAP
WITH THE SYSTEM HOT AND UNDER PRESSURE
BECAUSE SERIOUS BURNS FROM COOLANT CAN
OCCUR.

NOTE: It is normal for the water pump to weep a
small amount of coolant from the weep hole (black
stain on water pump body). Do not replace the
water pump if this condition exists. Replace the
water pump if a heavy deposit or a steady flow of
engine coolant is evident on water pump body from
the weep hole (shaft seal failure). Be sure to perform
a thorough analysis before replacing water
pump.

(1) Drain cooling system (Refer to 7 - COOLING -
STANDARD PROCEDURE).

(2) Remove accessory drive belts (Refer to 7 -
COOLING/ACCESSORY DRIVE/DRIVE BELTS -
REMOVAL).

NOTE: The water pump is driven by the timing belt.

(3) Remove engine timing belt (Refer to 9 -
ENGINE/VALVE TIMING/TIMING BELT AND
SPROCKETS - REMOVAL).

(4) Remove water pump mounting bolts (Fig. 31).
Note position of longer bolt for proper re-installation.

(5) Remove water pump body from engine

Here is link to get a factory service manual relatively cheap.
2004 Chrysler 300M Service Manual Covers every serviceable part.

Have you Checked the Fan Clutch?