Heater problems

Hi,

The sensor doesn't actually control the heat. Its job is to tell the computer how hot or cold the coolant is.

Are you certain the coolant is full and there is no air in the system?

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Lets try this. Here are the directions for filling and bleeding the cooling system. Try it and see if it makes a difference. The attached pics correlate with the directions.

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2002 Mercury Grand Marquis V8-4.6L VIN W
Draining, Filling and Bleeding
Vehicle Engine, Cooling and Exhaust Cooling System Service and Repair Procedures Draining, Filling and Bleeding
DRAINING, FILLING AND BLEEDING
Cooling System Draining, Filling And Bleeding

Draining

WARNING: Never remove the pressure relief cap under any conditions while the engine is operating. Failure to follow these instructions could result in damage to the cooling system or engine and/or personal injury. To avoid having scalding hot coolant or steam blow out of the cooling system or reservoir, use extreme care when removing the pressure relief cap from a hot cooling system or reservoir. Wait until the engine has cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly until pressure begins to release. Step back while the pressure is released from the cooling system. When certain all pressure has been released, remove the pressure cap (still with a cloth).

CAUTION: The coolant must be recovered in a suitable, dean container for reuse. If the coolant is contaminated it must be recycled or disposed of correctly and replaced.

CAUTION: Some vehicle cooling systems are filled with Motorcraft Premium Engine Coolant VC-4-A (in Oregon VC-5, in Canada CXC-10) or equivalent meeting Ford specification ESE-M97B44-A (green color). Others are filled with Motorcraft Premium Gold Engine Coolant VC-7-A or equivalent meeting Ford specification WSS-M97BS1-A1 (yellow color). Always fill the cooling system with the same coolant that is present in the system. Do not mix coolant types.

NOTE: Less than 80% of coolant capacity can be recovered with the engine in the vehicle. Dirty, rusty or contaminated coolant requires the system flush and replacement

1. Release the pressure in the cooling system by slowly turning the pressure relief cap one-half turn counterclockwise. When the pressure is released, remove the pressure relief cap.
2. Place a suitable container below the radiator draincock and drain the radiator
3. Close the radiator drain cock.

Filling-Bleeding

CAUTION: Engine coolant provides freeze protection, boil protection, cooling efficiency and corrosion protection to the engine and cooling components. In order to obtain these protections, the engine coolant must be maintained at the correct concentration and fluid level in the degas bottle.
When adding engine coolant, use a 50/50 mixture of clean, drinkable water and engine coolant.
To maintain the integrity of the coolant and the cooling system:
- Add Motorcraft Engine Coolant VC-4-A (in Oregon VC-5, in Canada CXC-10) or equivalent meeting Ford specification ESE-M97B44A (green color), or Motorcraft Premium Gold Engine Coolant VC-7-A or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Always fill the cooling system with the same type of coolant that was drained from the system. Do not mix coolant types.
- Do not add orange-colored Motorcraft Specialty Orange Engine Coolant VC-2 or equivalent meeting Ford specification WSS-M97B44D. Mixing coolants may degrade the coolant's corrosion protection.
- Do not add alcohol, methanol or brine, or any engine coolants mixed with alcohol or methanol antifreeze. These can cause engine damage from overheating or freezing.
- Do not mix with recycled coolant unless it meets the requirements of Ford specification ESE-M97B44-A or WSS-M97B51-A1. Not all coolant recycling processes meet these Ford specifications. Use of such a coolants may harm the engine and cooling system components.

1. Remove the thermostat.
2. Disconnect the heater core coolant supply hose from the fitting at the rear of the manifold.

Pic 1

3. Add the coolant/water mixture through the thermostat opening until coolant appears at the heater core coolant supply outlet fitting at the rear of the manifold.
4. Install the heater hose, using an appropriately sized worm style damp in place of the constant tension clamp.
5. Reinstall the thermostat gasket (O-ring) and the thermostat.
6. Add the correct engine coolant mixture to the degas bottle until the coolant level is between the "COOLANT FILL LEVEL" marks and replace the pressure cap.
7. Select the maximum heater temperature and blower motor speed settings. Position the control to discharge air at the A/C vents in the instrument panel.
8. Run the engine until it reaches operating temperature.

9. CAUTION: If air discharge remains cool and the engine coolant temperature gauge does not move, the engine coolant level is low in the engine and must be fired. Stop the engine, allow it to cool and fill the cooling system.

Add the correct engine coolant mixture to the degas bottle until the coolant level is between the "COOLANT FILL LEVEL" marks.
10. Repeat the two previous steps until the engine coolant mixture is between the "COOLANT FILL LEVEL" marks on the degas bottle. Turn off the engine and allow it to cool.
11. Check the freeze protection of the engine coolant mixture with the Battery/Anti-Freeze Tester 014-R1060 or equivalent. Adjust freezing point range if necessary.

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Based on your description, I suspect you have an air pocket in the cooling system. Let me know if this helps.

Take care,
Joe