Where is the thermostat in a 2004 Chevy Impala?

Answer 1

If you follow the upper radiator hose to the engine, you will see it is clamped on to the thermostat housing that is held on with two bolt to the intake manifold. When you take out the two bolt for the thermostat housing the thermostat sits under the housing.

You might think it should only take minutes to replace the thermostat. But due to the minimal amount of clearance between the thermostat housing and exhaust cross over pipe, it took me hours (and my wife's small fingers). Some suggest that the cross over pipe be removed first. In Hind site I believe that might be true. However, anyone who has disassembled exhaust components knows the nightmares waiting there; rusted fasteners are always difficult to remove and often break.

I settled for disconnecting the three hoses from the coolant manifold tube and removing the one nut which stabilizes it on the thermostat end of the intake manifold. The coolant manifold tube can then be moved enough to gain some room without completely removing it. Leave the other end connected. Also disconnect the sensor wires from the air cleaner boot and remove it too.

One of the two capscrews which hold the thermostat housing in place can be removed easily with the right size socket, six inch extension, and ratchet. It is the second, "demon" capscrew, which will demand hours of your life before surrender.

I purchased one of those ratchet type, boxed end wrenches with a swivel head to access the second capscrew. A word of warning; do not loosen this capscrew with the ratchet end of the wrench to the point that the wrench can not be taken off the head of the capscrew. As you back the capscrew out, you lose clearance between the head of the capscrew and cross over pipe to the point that you can't get your wrench off the capscrew. Due to the nature of the wrench and its ratchet feature, it will only turn the capscrew in one direction. You can't tighten the capscrew to get your wrench back!

Once the two capscrews are removed, a bit of twisting and turning of the thermostat housing and poking with a screw driver to separate the thermostat will allow both parts to come free. Be sure to retrieve the rubber gasket washer from the old thermostat. Inspect the thermostat housing and capscrews for damage and replace, as required. You will now notice that the housing has one hole and one slot. There is no doubt that both capscrews have to be removed completely to free the housing for this method, despite the slotted hole. For the effort so far definitely get a new thermostat before assembling even if you determine the "old" one is still good.

Position the new thermostat in the intake manifold, spring side first. Delicately place the thermostat housing over the thermostat and hopefully it will remain in place. More than likely it will be knocked loose while trying to position the thermostat housing. Use a screw driver carefully to put the thermostat back in place. I tried to start the demon capscrew first before positioning housing but it only got in the way. With that slot in the housing I thought it might be the way to go; didn't work.

Once the housing is in position, install the "easy" capscrew finger tight to keep the parts in place. I then used a magnetic wand to help position the second capscrew in its threaded hole, but it took my wife's small hand to start the capscrew. Once the second capscrew was started, the rest all seemed easy; ten minutes it was all back together. One major footnote as far as I'm concerned. We used a slightly shorter capscrew (M8 1.25 x 20) in place of the demon capscrew. It was easier to "find" the hole, hold in place, and start threading into the hole.

Check the coolant level in the radiator. Make sure after you fill the radiator with coolant, you bleed the air out of the system. On the top of the thermostat housing you will see a bleeder screw. Open it up after the car is at operating temperature and bleed of the air. Let the coolant flow out till you have a steady stream of coolant.