How to Replace a Thermostat Housing – 2007 Ford Mustang

Friday night is fast approaching, but your sweet Mustang is out there leaking radiator fluid everywhere!

Your night out is not necessarily doomed; Ford Mustangs are notorious for their thermostat housing leaking. This would be the first place I would recommend you check if you are seeing radiator fluid leaking from your engine. It’s a fairly simple fix for anyone with a 5/16 socket wrench (or 8 mm), and the know-how I’m going to provide for you in the following paragraphs! So, let’s get to it!

Consider this for a minute: When you’re going to cook something that requires boiling water, do you use a metal pot, or do you grab a pot made of plastic to boil the water in? You choose a metal pot to boil the water in, right! Well, the Ford designers decided to choose a plastic pot to contain water that reaches boiling temperatures in their engines.

The thermostat housing, AKA: inlet housing, located at the top, front, on the Ford Mustang is made of plastic. For the reason pointed out above, this plastic housing is notorious for developing cracks and leaks which allow coolant to escape the system. If your engine is leaking coolant this would be the very first thing I would recommend you check.

Crack inside the bowl of thermostat housing.

Have a flashlight handy when you go to check the thermostat housing. It can be dark under the air intake and a flashlight will help illuminate the area. Leave the engine OFF and the key OUT of the ignition so there is no accidental start.

Refer to the photo for the location of the thermostat housing. Guide your flashlight beam around the top of the housing and below the housing. You’re looking for fluid pooled on top of it, or below it. You may even see drips off of it on the underside. If you see any of these telltale signs, then it is time to replace the thermostat housing.

Replacing the thermostat housing is one of the easy repairs a home mechanic to do.

First, you’re going to want to head over to your local auto parts store. Have the make, model and year of your Mustang with you, and the engine size IE: V6, Shelby, etc. available so the counter person can get you the correct replacement housing.

The replacement thermostat housing is going to be, again, plastic. That is the standard replacement, but you can find an aluminum replacement if you so choose. I found this little sweetheart on Amazon!

You are looking at paying twice as much for the aluminum, but it will far outlive the plastic replacement, but it’s up to you. The plastic will suffice as it has already.

Remove the Old Thermostat

  • A 8mm, or 5/16″ (8mm = 5/16″), socket wrench with an extension.
  • The new thermostat housing.
  • A dab of Vaseline, or some spit for the “O” rings.
  • Pliers for the hose clamps.
  • A little bit of patience for your own piece of mind.
  1. Remove the negative battery connection at the terminal post on the battery to avoid any accidents.
  2. Place a catch basin under the radiator and open the petcock to drain the radiator fluid (remember to keep this fluid away from your pets!). If your radiator is leaking, you may be able to skip this step due to the fluid already leaking out!
  3. Using your 5/16″, or 8mm, socket loosen the hose clamp on the air intake and pull the hose off. Bend it back and out of the way, or remove the air filter lid (which this hose is connected to) (un-clip wire connector) and remove it out of the way.

Now you have the metal piece the air hose was connected to. The thermostat housing is right underneath it. Using your 5/16″, or 8 mm, unscrew the four bolts holding the metal intake on. Set the metal piece up to the side without disconnecting it.

Remove the wire connector next to the air inlet.

Remove the retaining bolts.

  1. Unscrew the three bolts holding the thermostat retainer on. Move this piece out of the way by tucking it behind something. Remove the thermostat and put somewhere safe for re-installation. This might be a good time to test the thermostat.
  2. Using your pliers to squeeze the hose clamp, of the smaller hose, on top of the thermostat housing and pull the hose off.
  3. Disconnect the wire connection attached to the temperature probe installed on top of the thermostat housing.
  4. Take your 5/16″, 8mm, and remove the screws on top of the thermostat housing. Set them somewhere safe so you won’t lose them.
  5. Squeeze the hose clamp on the large hose located at the front of the housing, then grab the housing and maneuver it up and out.

Pay attention to the position these two sensors are connected to on the housing top.

Install the New Housing

  1. Remove the temperature sensor from the old housing (the one you just took off the engine) and put it into the new housing.
  2. There should be three new o rings in the box. The small o ring goes on the temperature sensor with a bit of Vaseline, or spit. The second, larger, flat, o ring goes underneath the housing. There is a machine groove it sets into. Again, use a bit of Vaseline, or spit, to ensure they seat properly. The third goes on top of the thermostat itself.
  3. Put the screws back in the top of the thermostat housing and torque to specification.
  4. Attach the temperature probe wire connection.
  5. Re-connect the water hoses and line up the hose clamps in their previous position.
  6. Place the thermostat into the new thermostat housing. Place the new large o ring on top of it, then secure the top with the screws. Torque to specification.
  7. Re-attach wire connections, air inlet with four screws and torque.
  8. Push air hose back on and tighten hose clamp. Re-attach lid of air filter if necessary.
  9. Check radiator petcock, is it closed snug?
  10. Fill system with coolant. Watch for leaking where you just installed the thermostat housing.
  11. Re-connect negative battery cable.

Start the car watching for leaks. Check radiator fluid level to make sure its filled to the minimum line.

YOU’RE DONE! Wasn’t that a piece of cake?! Good job! Now go enjoy your weekend!

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