Where is the thermostat on a Chevy Lumina 3100 engine?

Answer 1

The thermostat is at the left (driver) side of the engine under the air intake tube. To replace, drain the coolant, take off the engine air intake tube connected to the intake manifold on top of the engine and take off the air cleaner housing at the left side of the engine. Then take off the large coolant hose going to the engine on the left side. The thermostat is inside the cast aluminum flanged nipple housing that the large coolant tube is connected to. The bottom of the two bolts that connect the housing looks impossible to get at, but you can access 1/12 of a turn at a time with a standard open end wrench from under the exhaust. You do not need to remove the exhaust manifold, but getting behind and under it is tight. You do not need to completely remove both bolts that hold the flange on because the flange has an open slot. If you take out the bottom bolt, getting it started would be hard because it is quite hidden.