Replacing Ford Explorer / Ranger 4.0L V-6 Thermostat

Tools

1. 1/4in Drive Ratchet
2. 10mm Socket
3. Wobble Drive (or swivel adapter)
4. Socket Extension (possibly two)

Parts

1. Antifreeze and Flush (if desired)
2. Thermostat - Stant #29959 (195 deg) or a UAP/NAPA #33199
3. Rubber o-ring type gasket (no sealant required

   The Procedure

   Drain the coolant down below the thermostat level into a bucket.
   
   To make this job as easy as possible requires removing a few things. Also, watch out for the sharp rear edge of the fan shroud. First, the air duct from the MAF sensor to the throttle body must come out.
   Then get the accessory drive belt out of your way. This is very simple. Put a wrench on the spring-loaded tensioner and torque it to loosen the belt, then slip it off. The belt tensioner needs to be held in the tensioned position for access to the thermostat housing bolts, or it can be removed entirely. Removing the tensioner allows lots of room for you to put the thermostat housing back on.
   
   Next, there's a small wire harness running right through the area where ideally you'd like to stick your fingers to work that third bolt once you've loosened it. You can loosen the plastic clip holding this harness to the alternator bracket and move it out of the way (from the original position on the left of the housing to the right).
   
   
   
   Using a 1/4 drive ratchet with an extension connected to a swivel connected to an extension connected to a 10mm socket for getting the 3rd bolt in and out has been known to work. Beware of dropping the 10mm socket in that "next to impossible hole to get the socket out of area". Perhaps you should keep a magnetic retriever handy just in case.
   
   Pull the housing off with the hose still attached and then replace the thermostat. Then those famous words -- "Assembly is the reverse of disassembly." If you are having a little problem holding it all together, put a little 3M 8001 weather-strip adhesive on, just enough to keep it from falling out, no more.
   
   If your belt is more than maybe 40k old now's a good time to put a new one on. The old one should go in a Ziploc in the rear storage compartment for those road emergencies.
   
   Once you have installed the new thermostat you will need to burp the air out of the system. A simple procedure to do this is to add coolant and distilled water to the cold system until the fluid level is at the top of the radiator neck. Start the truck and let it warm up. When the thermostat opens and water begins to circulate, the traped air in the system should make its way to the filler neck. Keep adding distilled water to maintain the level at the top of the neck. After a while the coolant will warm up enough to start to expand, causing the coolant to start to rise in the neck on its own. When it does that, go ahead and put the cap back on, and top up the overflow bottle with coolant and distilled water to about two inches above the "cold fill" line.
   
   After driving the car for a day or two, check the level in the bottle and add as necessary. It's also a good idea to get the car up to full operating temp and check for leaks when the system pressure is highest.