Chrysler Repair: thermostat location, domestic water supply, heater hoses

Question
Hello,
I have a 1999 300m with a 3.5L HO engine. I believe the thermostat is stuck closed (no heat)
Where is the stat located on the engine? and could you give a brief replacement explanation.
Thanks
Mike "COLD IN CANADA"


Answer
I am not sure that the HO version is different from the other 3.5L engines, but if it is the same the thermostat will be found under the hemspherical manifold that is on the top of the intake manifold at the front of the engine and has the fat top radiator hose running into it at a nipple on the side of manifold. A couple of bolts hold the manifold in place and if you remove those the manifold will be detached so you can lift it off and retrieve the thermostat for replacement. The issue of no heat though may not be due to the thermostat unless you also observe that the temperature of the engine runs cool as shown on the gauge at the dash. Also I would suggest that you touch the in- and out-going heater hoses where they pass thruough the center of the firewall behind the engine. If one hose is hot and the other is noticeably cooler that would imply a plugged heater core that you might be able to clear by removing the heater hoses and flushing water in both directions with a domestic water supply-connected garden hose. If the temp of the engine is normal, and the hoses feel warm and about equally hot, then the problem may be with the temp door in the heater/ac unit in the cabin. The temp of the outlet air is controlled by changing the air distribution between the heater core and the ac evaporator core. If that door is jammed or out of adjustment you could have a source of heat that is adquate but the air would not pass through it.
By the way, if thermostat is making for too cool coolant situation, the thermostat is actually stuck open and preventing the temp of the engine from rising to around 200F by allowing the water pump to move it through the radiator to too a great a degree. It usually should begin to open around 195F, but if it were stuck open then the temp of the coolant could be much lower. The thermostat doesn't really control the coolant flow to the heater (there is a by pass) so it all depends on the thermostat not opening too soon to prevent the engine from warming up the coolant.
So I would look a the temp gauge, check the radiator hoses and then consider whether or not it is the thermostat. You can check the old one by putting it in a pot of hot water on the stove and with a thermometer see at what temp it begins to open. If you find it stuck open then you don't even have to test it, just get a new one. Inspect the o-ring or gasket and consider getting a replacement for that too; it may come with the thermostat if you replace it.
You will want to drain the system via the radiator drain cock, down a few quarts, into a pan so that when you open the manifold you don't have coolant flowing over the intake manifold and onto the floor of the garage.
Roland