How to you replace the thermostat in a 3.1l gm engine

3.1 Thermostat replace
You'll want some pretty good lighting. If you were thinking of investing in some shop lights for your garage,now would be a good time.

Tools required from memory:
1. 13 MM, 12 point, box end wrench for lowerthermostat housing bolt 2. 3/8 rachet 3. 3/8 drive 13 MM wobble socketor 13 MM short socket with universal joint for upper thermostat housing bolt. 4. 3/8 drive 6" extension 5. 9/32" socket or endwrench for bleeder screws
6. Channel Lock to release hose clamps. Also a normal pliers for the small clamps ifyou use Method 1.
7. Siphon tube
8. Container to capture antifreeze
9. Latex gloves

Procedures:
1. Let the car cool down. 2. Siphon about a gallon ofantifreeze from the radiator. 3. Follow the top radiatorhose on the driver's side to the engine and remove the hose from the thermostathousing. The thermostat is under thethermostat housing. There is no gasketbecause the thermostat has a rubber ring built onto it. 4. Remove the rigid PCVintake hose from air inlet duct
5. Loosen the air inlet duct clamps onthe air cleaner and throttle body, and move the duct aside. This is a perfect time to check the aircleaner element and clean the housing of debris. 6. There are couple of methodsyou can use to remove the thermostat housing. Method 1. Remove the throttle body. You will need a new throttle body gasket butit makes getting at the lower thermostat housing bolt easier. You will also need to remove the littlecoolant hoses that feed the throttle body. It does give you the opportunity to clean the throttle body withcarburetor cleaner if you wish. Thismethod requires no more explanation since the thermostat housing lower boltwill be fairly accessible. Method 2. Do not remove the throttle body. You will not need any parts other than thethermostat, but you have very little room to move your wrench on the bottom thermostathousing bolt, which makes it slow going. It generally requires you to remove one coolant line from the heatercore where it connects to the steel tube by the throttle body in order to getthe lower bolt back in, depending on the length of your fingers. a. Optionally, remove the heater hose that runsto the metal tube near the throttle body. You can get the lower bolt out without this step. The problem I have without this step isgetting the lower bolt back in.
b. Remove the lower bolt first. Youwill need to maneuver your hands both under the exhaust manifold on the frontside and from behind the exhaust manifold on the back side to move the 13 MM boxend wrench 30 degrees at a time. This iswhy you need a 12 point box end. Youcould try the ratcheting box end wrench, but when it starts to get loose, it'stough to put enough friction on it for the ratchet to work. You will hear people talk about how thehosing is slotted so you don't need to remove it all the way. That is false. That only works on old 3.1s that have a longstud and nut. You cannot remove thethermostat housing without removing the bolt because the thermostat extendsinto the thermostat housing for longer than the bolt. (Been there, tried that.)
7. Remove the upper bolt with the 13 MMsocket, universal joint, extension, and ratchet. 8. Clean the face of thethermostat housing and recess there the thermostat fits into the inlet manifoldin the thermostat rubber seal contact area.
9. Insert the new thermostat goes intothe inlet manifold, spring end first. Make sure it is in all the way so the rubber ring does not get pinchedwhen you tighten the thermostat housing down on top of it.
10. Replace the thermostat housing.11. Usingthe 9/32" wrench or socket, open the bleeders on the thermostat housing andwater pump. The water pump is located onthe passenger side on the front of the engine on the steel water manifold.
12. Pour as much antifreeze as will fitinto the radiator.
13. Start the engine to bring it up totemperature, and turn on the heater.
14. While it's running, watch the bleeders. When antifreeze starts to come out of ableeder, close that bleeder.
15. When the thermostat opens, the levelin the radiator will drop and you will be able to pour in most of the the remainderof the anti-freeze. Then replace the cap. Pour the little remaining into the reservoir.