Where is the thermostat located on a 1994 Pontiac Transport V6?

If you have the 3800 series engine (3.8L), then the thermostat can be found under the alternator. Do not attempt to replace it if the engine has been run within the past hour and a half, as the coolant may still be hot enough to burn you. Remove the positive cable from the battery. Look for the tensioner pulley along the serpentine belt route and pry it towards the radiator with a 3/8" or 1/2" ratchet while you or a helper carefully slip the loosened belt over the alternator pulley; you may need someone to point this pulley out to you. Next, remove the front and rear bolts that hold the alternator. Wiggle the alternator forward and backward until it's free. Place it aside and take care not to damage the wires going to it. Now you should be able to see a large black hose under where the alternator was. The following steps will involve spilling anti-freeze, so I suggest spreading cat litter under the engine or laying down old towels or using a large drainpan to contain the leakage. Loosen the hose clamp and pull that end of the hose off of the thermostat housing. Romove the two bolts holding this housing down, and carefully tap the housing with a hammer handle or screwdriver handle if you can't simply pull it off. You will find the old thermostat in the housing or still on the block. If the thermostat has dirt or debris on it and appears to have been blocked or stopped up by this, you will need to flush the radiator and cooling system. Now you will need to lightly scrape all of the old gasket material off of the housing and mating location on the engine block. Follow directions with the thermostat to ensure proper installation of the new gasket. Insert the spring side of the thermostat into the engine block and place the housing on top, carefully alligning the bolt holes. Start the bolts by hand and rotate them at least three complete turns to prevent cross-threading the bolts. Snug these bolts down but do not over-tighten. Finish the job by reversing these directions, but make sure the serpentine belt is centered on ALL of the pulleys before starting the engine. After engine start, refill coolant tank and watch for leaks around the repair area. Check your coolant over the next few days and weeks to ensure you aren't leaking.