Below is how I replaced the thermostat on a 2004 Chevy Monte Carlo 3.4L OHV engine 'with out" removing the exhaust cross over pipe which every manual says you have to remove. This may work on other years and models. It took about 3 hours but could be done in less time if you decide not to clean the throttle body.

Removing the throttle body provided good access to remove the thermostat housing, bolts and thermostat. A shorter 13MM box end wrench will make it easier to remove the thermostat housing bolts.

Buy the following-
Throttle body gasket
Thermostat with rubber seal (should come with the thermostat).
Optional- NAPA heater hose part number 10030 (quantity of 1) which can be cut to replace the small 2 hoses going into the lower side of the throttle body. Will also need 4 new small hose clamps since the outside diameter of this hose is slightly larger than the stock hose.

Disconnect all electrical connectors on the throttle body and air intake hose and pull the harness out of the way.
Remove the air intake hose, cover for air filter housing and air filter.
Remove the three bolts holding the accelerator cable support bracket to the throttle body (one bolt is hidden under the throttle body). Disconnect the throttle cable and cruise control cable from the throttle and set the entire assembly out of the way. You do not need to remove the cables from the bracket.
Drain the cooling system.
Remove the nut holding the steel heater pipe assembly to the bottom of the throttle body.
Remove the clamps on the two small coolant hoses which attach to the bottom of the throttle body. These two hoses can be replaced using NAPA part if you want.
I pulled the pipe down to access the lower throttle body bolt with a 13mm deep socket. You may want to remove the bolt which holds this pipe into the water pump housing which will allow you to move the pipe out of the way and make it easier to get at the lower throttle body bolt.

Remove the upper throttle body bolt and the throttle body.

Remove the upper radiator hose from the thermostat housing, 2 bolts on the housing and remove the housing. If the thermostat sticks to the housing, insert a putty knife between the housing and the thermostat gasket to separate it. This will make it easier to remove the housing.

Clean everything and reassemble in reverse order. I use lithium grease on the hose fittings to make it easier to install the hoses.

It is a good idea to clean the throttle plate and inside the throttle bore removing the gunk but be careful not to get carburetor cleaner through the throttle shaft into the throttle position sensor because it will cause it to fail almost immediately. A small wire brush will help remove stubborn deposits.

When you go to put the thermostat housing back on, put some grease into the pocket in the intake manifold where the thermostat goes and place the thermostat into it to hold it in place. The hole in the thermostat housing for the lower screw is slotted. If you start this screw about 1 to 2 turns into the manifold then slide the housing over it, will be much easier to put the lower screw in.

Hope this helps someone.

 

fixed wording

 

**BUMP**

this is a nice write up

one of the modorators should move it into the "how to" section for a referance so that it does not get lost over here.

just my $0.02

 

What is the screw/bolt that is right in the middle of the thermostat housing, right after you connect the radiator hose?

 

I believe that is a coupling for one of the heater hoses. If you follow it through, , it probably goes up to the firewall.

 

Maniac,

That's not it, it's right in the middle of the goose neck going back towards the housing. It looks like it might be copper, it's just sitting right in the middle of the part.

 

If this is a 3400, you are not talking the t-stat housing (that's on the driver side of the engine). You are talking the heater tube that comes straight up from the water pump housing (it's above the radiator hose that connects with the pump). The tube runs the length of the valve cover and coils around the back.
That bolt/screw is brass, on the passenger/right side of the engine. It's a air bleeder valve. When you drain the system, it's to assist with bleeding air out of the car.

The 3800 has a bleeder valve similiar to that above the T-stat housing.

 

It's the t-stat housing, it's coming from the top hose of the radiator into the engine, on the driver's side. It has some screw/bolt in it. But, as you said, it could be a bleeder valve.

 

Ok, in the middle of tightening things up from changing t-stat. Can someone tell me if I need to bleed the system?

Also, is there a way of looking at it to see if it is bad?

Please someone answer quick so I can finish.....Thanks

 

I just joined to post on this method of installing the thermostat on the 3400 engines. I did this on my 2003 impala and had great success with removing the throttle body. I spent about an hour trying to figure out how to loosen that lower bolt on the thermostat housing and found this thread after giving up. I had reassembled everything, well an hour later have my thermostat installed and my car is running better than ever. My transmission is also running a lot better. I was getting a P028 code (low coolant temp) and this was just the ticket. Just want to say thanks to the original poster.

I didn't replace the throttle body gasket, I will probably just pick one up really soon and replace it anyway. Everything looked good and appeared to have a good seal, but don't really want to risk having issues down the road over an easy to replace gasket.