Replacing Ford Explorer / Ranger
4.0L V-6 Thermostat

This section is a compilation of suggestions and advice from many authors. I believe the entire list to be: Dr. Bob, Bill Spikes, James Hammond, Dan Ciarlette, Steve Offiler, Dick O'Keefe, Mike Iglesias, and myself. Also, if your temperature gauge read consistently low the temperature sender might be the culprit. See below for how to fix that problem.

The Raw Materials


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


  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. And don't let your dog or cat drink from the 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).

The suggestion to stick the bolt to the socket with a bit of duct tape for re-assembly is a very good one. You should also stick the socket to the extension you'll be using (about 6" I think) else you'll leave the socket neatly stuck to the bolt when you try to pull it off.


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 ubiquitous 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 car and let it warm up. When the thermostat opens and water begins to circulate, the entrained 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.

Replacing the Temperature Sender

The temperature sender is just upstream of the thermostat. You can change this on a cold motor without draining any coolant. There's a trick to using a piece of rubber hose to guide the new sender into the threads down amongst the wires and heater hoses, too. The time to change is less than ten minutes, of which six will be head scratching. The sender itself is less than $10 at most parts stores. You'll want a deep socket to loosen the old one.




Updated November 22, 1998

All contents of this site Copyright 1997, 1998, 1999 Jeff Singleton. ALL RIGHTS RESERVED.