How do i remove rhe thermostat from the housing in a 2004 GMC Envoy

It pretty much boils down to removing the thermostat housing and removing the theremostat and reversing this procedure to install. How you must actually go about this can vary depending on which engine your Envoy is equipped with. On some of the newer engines, the entire thermostat housing must be replaced.

The thermostat is located on the driver's side of the engine. It is difficult to see, but it is behind the alternator. The lower radiator hose goes to a metal tube, that is part of the thermostat housing. Below is a picture of thermostat and temp sensor location (alternator removed).

The thermostat on this vehicle's In-line 6 cylinder engine is on the driver's side of the engine, below & behind the alternator. You have to remove the alternator to gain access to the thermostat housing. You also need to disconnect the battery before you remove the alternator to avoid sparks and shorts.

Most directions outline removal of the alternator to gain easy access to the hose clamps, bolts and housing of the thermostat. I have located a site that after free registration, has detailed instructions on how to do this job, and the link below that describes an easier method with photos. Check out:

http://forums.trailvoy.com/showthread.php?t=54225&highlight=replace+thermostat

at the front of the engine, right behind the alternator, you have to remove the alternator to change the thermostat.

The thermostat is located inside the thermostat housing. To find it follow the upper radiator hose to the engine block.
Depending what size of engine you have the location is different.
The thermostat on this vehicle's (the Envoy & Trailblazer are essentially the same vehicle) In-line 6 cylinder engine is on the driver's side of the engine, below & behind the alternator.
If you have a V8 cylinder engine is in front of engine see the picture. Item 303 thermostat housing, 305 thermostat, and 304 thermostat gasket.

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.

It's actually very simple. Follow the upper radiator hose to the top of the engine block. You will see a housing which the hose is attached to. Remove the hose from the housing. The housing will have 2 or 3 bolts holding it down. Remove the bolts and lift the housing off. The thermostat will be sitting there and you simply need to remove it.

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:


Thermostat mounting—4.2L engine

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.
   

The thermostat on this vehicle's (the Envoy & Trailblazer are essentially the same vehicle) In-line 6 cylinder engine is on the driver's side of the engine, below & behind the alternator. It is not found in the typical location (which may be for the 8 cylinder engine), in an answer above.

Most directions outline removal of the alternator to gain easy access to the hose clamps, bolts and housing of the thermostat. I have located a site that after free registration, has detailed instructions on how to do this job, and the link below that describes an easier method with photos. Check out:

http://forums.trailvoy.com/showthread.php?t=54225&highlight=replace+thermostat

4.2L Engine the thermostat and the neck where the hose goes on is one unit $25 at autozone

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