Is it necessary to remove the thermostat housing in order to replace a water pump bypass hose? Mechanic advises that my 2000 Mountaineer's small by-pass hose is leaking. In order to replace it, either the water pump or thermostat must be removed. I am not replacing upper or lower radiator hoses.

Removal & Installation

1. Before servicing the vehicle, refer to the Precautions section.
2. Drain the coolant.
3. Remove or disconnect the following:
   
   Negative battery cable

Upper fill panel, if equipped
AIR injection control valve, if equipped
Air cleaner
Oil level indicator tube nut, if necessary
Water pump belt cover
Water pump drive beltLower radiator hose
Thermostat bypass hose from the coolant inlet housing
Water pump cover

Remove the water pump by rotating it clockwise using special Tool J 38816-1A (water pump remover/installer).
To install:
Install the water pump with a new O-ring, by turning it counterclockwise using the special tool, until it stops. Torque the water pump to 73 ft. lbs. (100 Nm).

Install or connect the following:

Water pump cover. Torque the bolts to 89 inch lbs. (10 Nm).
Lower radiator hose
Thermostat bypass hose to the coolant inlet housing
Water pump drive belt
Water pump belt cover
Oil level indicator tube nut, if necessary
Air cleaner
AIR injection control valve, if equipped
Upper fill panel, if equipped
Negative battery cable

• Refill and bleed the cooling system.

Run the engine and check for leaks.

That is called the bypass hose. It could be leaking but I'd take a closer look at the thermostat housing. If you replaced only the thermostat and not the housing, the housing may be leaking. It's a common source of coolant leaks.

2001 Cadillac Deville 4.6L SFI DOHC 8cyl Removal & Installation procedure...

1. Before servicing the vehicle, refer to the Precautions section.
2. Drain the coolant.
3. Remove or disconnect the following:
Negative battery cable
Upper fill panel, if equipped
AIR injection control valve, if equipped
Air cleaner
Oil level indicator tube nut, if necessary
Water pump belt cover
Water pump drive belt
Lower radiator hose
Thermostat bypass hose from the coolant inlet housing
Water pump cover

4. Remove the water pump by rotating it clockwise using special Tool J 38816-1A (water pump remover/installer).

To install:

1. Install the water pump with a new O-ring, by turning it counterclockwise using the special tool, until it stops. Torque the water pump to 73 ft. lbs. (100 Nm).

1. 
   
   

Fig. To ensure proper operation, be sure to install a new O-ring (click for zoom)

2. Install or connect the following:
Water pump cover. Torque the bolts to 89 inch lbs. (10 Nm).
Lower radiator hose
Thermostat bypass hose to the coolant inlet housing
Water pump drive belt
Water pump belt cover
Oil level indicator tube nut, if necessary
Air cleaner
AIR injection control valve, if equipped
Upper fill panel, if equipped
Negative battery cable

3. Refill and bleed the cooling system.
4. Run the engine and check for leaks.


Hope this helps (remember to rate this comments)

Follow your upper radiator hose to the thermostat housing there should be 2 nuts holding it on.Remove the 2 nuts and gently pry it away from the intake manifold.lift the housing and remove the thermostat. When putting it back together be sure you clean both surfaces and use a water pump sealer on the thermostat housing and bolt back in place and attach any hoses or accessories that you might have removed in order to make it easier to remove.

4.8L, 5.3L and 6.0L Engines To Remove:
CAUTION
The thermostat is not serviceable separately. The thermostat housing (water pump inlet) and thermostat must be replaced as an assembly.

1. Remove the radiator outlet hose.
   
   
2. Remove the bolts from water pump inlet.
3. Remove the water pump inlet from the water pump.

To Install:

1. Install the water pump inlet to the water pump.
2. Install the water pump inlet bolts.
   • Torque to: 11 ft-lbs. (15 Nm)
3. Install the radiator outlet hose.

6.6L Engine To Remove:

1. Before servicing the vehicle refer to the precautions at the beginning of this section.
2. Drain the engine coolant.
3. Remove or disconnect the following:
   • Water outlet 6.6L Thermostat housing removal
     
     
   • Bolt for the fuel line bracket
   • Thermostat housing cover bolts
   • Thermostats and seals

To Install:
6.6L Thermostats and seals

1. Install or connect the following:
   • Thermostats and seals to the thermostat housing NOTE: The rear thermostat (D) has 2 vent valves. Install with the vent valves towards the rear of engine.
     
   • Thermostat housing cover with a NEW gasket
   • Thermostat housing cover bolts and tighten the bolts
     1. Torque to: 15 ft. lbs. (21 Nm)
   • Fuel line bracket bolt and tighten the bolt
     1. Torque to: 15 ft. lbs. (21 Nm)
   • Water outlet
2. Fill the engine with coolant.
3. Test drive the vehicle to confirm the repairs.

8.1L Engine To Remove:

1. Before servicing the vehicle refer to the precautions at the beginning of this section.
2. Drain the cooling system.
3. Remove or disconnect the following:
   • Inlet hose from the water outlet Water outlet and thermostat removal
     
     
   • Water outlet bolts (B)
   • Water outlet (A)
   • Thermostat (C)

To Install:

1. Install or connect the following:
   • Thermostat
   • Water outlet
   • Water outlet bolts and tighten the bolts.
     1. Torque to: 22 ft-lbs (30 Nm)
   • Inlet hose to the water outlet
2. Fill the cooling system.
3. Test drive the vehicle to confirm the repairs.

WARNING: SCALDING HOT COOLANT, WATER OR STEAM
NEVER remove the pressure relief cap under any conditions while the engine is operating. Failure to follow these instruction 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.

1. Wait until the engine has cooled.
2. Wrap a thick cloth around the pressure relief cap and turn it slowly (until the pressure begins to release.
3. Step back while the pressure is released from the cooling system.
4. When you are certain all the pressure has been released, (still with a cloth) turn and remove pressure relief cap .

REMOVAL

1. Drain the engine cooling system so that the engine coolant level is below the water thermostat (8575).
2. Raise vehicle on hoist. See General Information.
3. Disconnect the lower radiator hose (8286) and degas bottle hose from the water inlet connection.
4. Remove the two water inlet connection retaining bolts. Remove the water inlet connection.
5. Remove the O-ring seal and water thermostat from the water thermostat housing. Inspect O-ring for damage and replace if necessary.
6. If required, remove water bypass hose from water thermostat housing and remove water thermostat housing retaining bolts, water thermostat housing and O-ring from oil filter adapter (6881). Inspect O-ring for damage and replace if necessary.

INSTALLATION

1. Install the water thermostat, O-rings, water thermostat housing (if removed) and water inlet connection as illustrated.
2. Install and alternately tighten the retaining bolts. Tighten bolts to 20-30 Nm (15-22 ft. lbs.).
3. If removed, connect the water bypass hose to the water thermostat housing.
4. Connect the lower radiator hose and degas bottle hose to the water inlet connection.
5. Lower vehicle.
6. Fill the coolant with Ford Premium Cooling System Fluid E2FZ-19549-AA or-B (in Oregon, F5FZ-19549-CC, in Canada, Motorcraft CXC-8-B) or equivalent that meets Ford specification ESE-M97B44-A in a 50/50 mixture with water.
7. Start the engine and check all hoses and connections for leaks. Allow the engine to warm up so that the water thermostat opens.
8. Stop the engine. Top off degas bottle as required to maintain minimum cold fill level.

Please see my tip at http://www.fixya.com/cars/r5929960-s_thermostat .

Specific instructions for your car are as follows. Let me know if you get stuck or have more questions.

Removal & Installation

4.2L Engine

1. Remove the necessary coolant from the radiator.
2. Remove the alternator, as outlined in the Engine Electrical Section.
3. Loosen the outlet hose clamp at the thermostat housing. Remove the outlet hose from the thermostat housing.
4. Remove the thermostat housing bolts.
5. Remove the thermostat housing from the engine block.
6. Clean all of the surfaces of the thermostat housing.
7. Clean the sealing surface of the engine block.
   

To install:

1. Install the thermostat housing to the engine block.
2. Install the thermostat housing bolts and tighten to 89 inch lbs. (10 Nm).
3. Lubricate the inner diameter of the radiator hose with engine coolant.
4. Install the outlet hose to the thermostat housing. Secure the hose with the clamp.
5. Install the alternator.
6. Fill the cooling system with specified coolant and concentration.
7. Inspect all sealing surfaces for leaks after starting the engine.

5.3L Engine
NOTE The thermostat is not serviceable separately. The water pump inlet and thermostat must be replaced as an assembly.

1. Drain the cooling system to a level below the thermostat.
2. Remove the radiator outlet hose.
3. Remove the water pump inlet bolts.
4. Remove the water pump inlet and thermostat from the water pump.

To install:

1. Install the thermostat and thermostat housing to the water pump.
2. Install the thermostat housing bolts. Tighten the bolts to 11 ft. lbs. (15 Nm).
3. Install the radiator outlet hose.
4. Properly fill the engine cooling system and check for leaks.

It Depends on which engine you have, this is how it goes for both. I use a little RTV with a new ring as well.

THERMOSTAT REPLACEMENT (4.2L ENGINE)
Removal Procedure
1. Remove the necessary coolant from the radiator.
2. Remove the generator.
3. Loosen the outlet hose clamp at the thermostat housing. Remove the outlet hose from the thermostat housing.
4. Remove the thermostat housing bolts.
5. Remove the thermostat housing from the engine block.
6. Clean all of the surfaces of the thermostat housing.
7. Clean the sealing surface of the engine block.
Installation Procedure
1. Install the thermostat housing to the engine block.
2. Install the thermostat housing bolts.
Tighten: Tighten the bolts to 10 N.m (89 lb in).
3. Lubricate the inner diameter of the radiator hose with engine coolant.
4. Install the outlet hose to the thermostat housing. Secure the hose with the clamp.
5. Install the generator.
6. Fill the cooling system with specified coolant and concentration. Follow the correct cooling systen bleed procedure for your engine.
7. Inspect all sealing surfaces for leaks after starting the engine.
THERMOSTAT REPLACEMENT (5.3L ENGINE)
1. Drain Radiator and remove the radiator outlet hose.
2. Remove the water pump inlet bolts.
3. Remove the water pump inlet and thermostat from the water pump.
Installation Procedure
IMPORTANT: The thermostat is not serviceable separately. The water pump inlet and thermostat must be replaced as an assembly.
1. Install the thermostat and thermostat housing to the water pump.
2. Install the thermostat housing bolts.15 N.m
3. Install the radiator outlet hose.
4. Fill the cooling system with specified coolant and concentration. Follow the correct cooling systen bleed procedure for your engine.
5. Inspect all sealing surfaces for leaks after starting the engine.

passenger side (rt) of engine, middle. Be ery careful tightening the bolts so you don't break the pipe. Locate thermostat with jiggle valve facing up.

It is very hard to bleed air from system when refilling. see files if you don't have heat when done.

go here too

http://groups.yahoo.com/group/villagerquest/

Housing Removal

1. Drain the cooling system; refer to Cooling System Draining, Filling And Bleeding .

1. Remove the upper radiator hose.
   1. Remove the hose clamp bolt.
   1. Remove the hose clamps.
   1. Remove the upper radiator hose.

1. Remove the water bypass hose.
   1. Remove the clamps.
   1. Remove the bypass hose.

1. Remove the thermostat housing.
   1. Remove the bolts.
   1. Remove the thermostat housing.

Installation

1. CAUTION: Do not reuse hose clamps. Make sure new hose clamps are seated correctly.
   NOTE: Make sure the thermostat housing and mating surface are clean of dirt and old silicone.
   NOTE: Apply a 2.0-3.0 mm (0.079-0.118 inch) bead of Silicone Gasket and Sealant F7AZ-19554-EA or equivalent meeting Ford specification WSK-M2G343-A4 to the mounting surface of the water pump.