dcm0123

Decided to post in this forum as well since same engine is used in Impala's

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 most manuals say 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.

capucine

One way or the other it is a pain in the neck to change the thermostat on the 3.4 when you consider that it is a matter of 15 minutes with other engines like the 3.9 from GM. Manufacturers should consider this item when they build their vehicles because this part does not last a lifetime.

billharmon2

I have to remove the throttle body on my 3.4 impala to clean out the egr port. My thermostat is going so I will replace it at the same time. Your post could not have come at a better time.

DieselOne

I am about to tackle the thermostat on my 3.4L Impala and was sure pleased to hear/see that it can be done without removing the exhaust crossover pipe. Thanks for the articles here on this forum.

Jonathan Bourland

Same here.. this guide will be invaluable. Many thanks!

crawdad

I came across this post researching another repair. Just want to add - and I know it's an old post - that it can be done without removing the TB using common wrenches, although I may have used a half moon wrench at some point; it was a few years ago. There's also a youtube video with a similar procedure.

Mike1013

Very good information here. I have the shop manuals for my 2001 Pontiac Grand AM 3.4 l V6 and it said to remove the crossover pipe in order to remove and replace the thermostat. Ended up I bought a u-shaped wrench from Napa that fit under the crossover pipe, 13 mm 12 point, and there was barely enough clearance to get on the lower bolt. I can only turn the ranch about 15° at a time but finally got the boat loose enough where I could wiggle my hand into the very tight spaces and unscrew the bolt. I was able to get the top bolt out using an extension with my ratchet. On reassembly, from my experience, put the bottom bolt in first then you can line up the top bolt otherwise you will be trying 25 times like I did. There is roughly 2 in to work with and you can only see the lower bolts with a flashlight in one small area. I am 75 years old with lung cancer so I could only work about 5 minutes then rest 10 minutes so it took me 6 hours. I should have taken it to a garage but I still like to do things myself if I can. I suppose it would be easier to remove the throttle body but I did not do that. You can search for the u-shaped tool on Google by looking for GM thermostat wrench for 3.4 l engine. It cost about $20.