QuestionThe car runs well, but the temperature indicator never moves off the C mark. I believe this is the reason the car only blows cold air. The fan and heat power head was replaced a year or so ago, but I do not believe it to be the cause of this problem. It has a 2.7 liter motor.
AnswerHi Tom,
I wonder if you have a thermostat mounted in the thermostat housing of the engine, or if so it might be stuck open. Could someone have removed it? Do the heater hoses feel equally quite hot after you have been driving for a while? They are behind the engine and pass through the firewall. The thermostat housing is found by tracing the lower radiator hose back to the engine where it is mounted.
Another possibility is that the temp sensor is inaccurate so the temp gauge is also inaccurate. Nearby to the thermostat housing is the coolant temp sensor which has two wires: black/light blue and tan/black. The tan/black wire is connected to pin 26 of the engine control module. If you want to verify its accuracy you could measure the resistance across its terminal which should be 700-1000 ohms when the engine is at operating temp (but of course without a thermostat you won't get the coolant hot enough to bring the resistance down to that level). However an inaccurate gauge/sensor would not cause a too cool operating temp of the engine. So see whether you think the engine is really heating up the coolant or not by touch.
There are several steps to removing the thermostat housing to check the thermostat presence and that it if there that it opens only when if placed in hot water when it reaches 190F or so:
Disconnect negative cable from remote jumper terminal.
WARNING: DO NOT REMOVE PRESSURE CAP OR ANY HOSE WITH THE SYSTEM HOT AND UNDER PRESSURE BECAUSE SERIOUS BURNS FROM COOLANT CAN OCCUR.
Drain cooling system (Refer to 7 - COOLING/ENGINE - STANDARD PROCEDURE).
Raise vehicle on hoist.
Remove right front wheel and belt splash shield.
Remove accessory drive belts (Refer to 7 - COOLING/ACCESSORY DRIVE/DRIVE BELTS - REMOVAL).
Remove lower generator mounting bolt.
Lower vehicle.
Disconnect generator electrical connectors.
Disconnect AC clutch and AC pressure sensor electrical connectors. Reposition wiring harness.
Remove oil dipstick and tube. Plug hole in oil pan where dipstick tube mounts with water tight stopper.
WARNING: IF HOLE FOR DIPSTICK TUBE IN OIL PAN IS NOT PLUGGED, COOLANT WILL ENTER OIL PAN. SERIOUS ENGINE DAMAGE CAN OCCUR.
Remove remaining generator mounting bolts. Remove generator.
Disconnect hoses at thermostat housing.
Remove thermostat housing bolts (Thermostat and Housing - 2.7L Engine).
Remove thermostat and housing.
Those are some ideas to check out.
Roland
PS Use the 'thank/rate' tab to get back to me with results, without having to wait for me to be available to take a question. There is a section for comments. While you are there, if you believe this answer merites my being nominated as 'espert of the month' I would appreciate that as I hope to be so in November!
