How to replace thermostat on 4.0L OHV V6

[Charlie]

Well, after replacing my thermostat I decided to do a write up on it. If you are needing to replace your thermostat, I highly recommend doing it yourself. It is easy to do, and very cheap.

Note: This is for the 4.0 OHV, not SOHC

First, a general disclaimer: I am not a Ford engineer, and do not work for Ford. Anything that you do, you do at your own risk.

Now to start. It should take about an hour to complete this, but giving yourself plenty of time is the first step. The tools I used are very common, and can be found just about anywhere.

Before you start, drain all of your coolant out of the car. This will make your life a lot easier down the road.


Tools used:
3/8" Drive ratchet
3/8" 2" drive extender
3/8" to 1/4" drive reducer
1/4" drive ratchet
10mm socket
8mm socket
Flathead screwdriver (not pictured)

Parts needed: Thermostat
New coolant

Now, where is the thermostat located?


It is on the end of the hose going to both the engine block and the radiator. It is where the hose bolts onto the block.

First off: The intake needs to go. Take off the latch for the filter, unplug the 2 plugs in the intake, and pull the vacuum line out. Now, unscrew the hose clamp with the flathead screwdriver, and remove intake.

Now there is that throttle cable cover there. That needs to be removed. Take you 8mm socket, and remove the 2 bolts holding that on.

After that is removed, remove the 3 bolts holding the hose on. These use the 10mm socket. It will take some experimentation with the different extenders/ratchets I have listed, but it can be done with just that. When you are loosening up the bolts and removing the hose, be prepared for coolant to leak from there. Have something underneath the front of the truck to catch it, Either an oil change pan or just some old towels.
Once removed, you will see this:


Please note that the thermostat shown in this picture is actually the new one, yours will not look that nice. It will also be wedged in there solid, and take some wiggling to remove.

When you place in the new one, be sure it is aligned the same way, and rotated the same way as the last one.

Now, put the hose back, and tighten in the 3 bolts. Then re-attach the throttle cable cover. Now put the intake back on. Be sure to re-attach both sensor plugs, and also the vacuum line.

Now, refill the coolant and burp the system.

You have now successfully changed your thermostat. Take it for a drive, then check for any leaks.


This is the old thermostat. Note how the gasket around it is worn and chipping.
Just remember, replacing your thermostat is easy to do yourself, and a lot cheaper too. Just take your time, and everything should go fine! If I have left anything out that you think should be added, be sure to add it or let me know!

[Charlie]

Quick addition: Information on burping the system.

Here is the official procedure from the Ford manual. If you have 4.0L OHV engine be sure to follow this procedure to get out all the air. It is also in your owners manual!

WARNING: NEVER REMOVE THE RADIATOR CAP UNDER ANY CONDITIONS WHILE THE ENGINE IS OPERATING. FAILURE TO FOLLOW THIS INSTRUCTION COULD RESULT IN DAMAGE TO THE COOLING SYSTEM OR ENGINE AND/OR PERSONAL INJURY. USE EXTREME CARE WHEN REMOVING THE RADIATOR CAP FROM A HOT RADIATOR. IF POSSIBLE, WAIT UNTIL ENGINE HAS COOLED, THEN WRAP A THICK CLOTH AROUND THE RADIATOR CAP AND TURN IT SLOWLY TO THE FIRST STOP. STEP BACK WHILE THE PRESSURE IS RELEASED FROM THE COOLING SYSTEM. WHEN YOU ARE SURE ALL THE PRESSURE HAS BEEN RELEASED, PRESS DOWN ON THE RADIATOR CAP (STILL USING A CLOTH), TURN AND REMOVE IT.

Draining

Shut off engine (6007) and allow to cool.

Remove the radiator cap (8100). Refer to above warning.

Attach a 9.5mm (3/8-inch) inside diameter hose on the radiator draincock (8115) to minimize loss of coolant when draining. (look under your radiator - passenger side)

Open radiator draincock and permit coolant to drain into a clean container. (spray a bit of PB on it, then unscrew it)

Remove drain plug on cylinder block (6010) to allow coolant to drain from engine, if necessary. (not needed)

Dispose of old coolant properly. Promptly clean up any spilled coolant.


At this point you may want to flush the system, there are many ways. You can use a kit.

I like disconnecting the heater hose at the heater control valve, and inserting a push connect garden fitting into both hoses with the clamp(one is a drain or can be blocked off and another part open (e.g. rad cap)). Make sure the hose isn't on full blast(1/4-1/2 is fine since the heater core is fragile). You can flush a variety of ways (heater core, block, radiator) depending on the hose configuration.


Filling

WARNING: USE CAUTION WHEN ADDING COOLANT MIXTURE TO RADIATOR TO AVOID HOT COOLANT OR STEAM BLOW OUT FROM THE RADIATOR.

NOTE: Use the following steps to remove air from the cooling system and to make sure fill is complete. (VERY IMPORTANT FOR THE 4.0L)



NOTE: When filling a crossflow radiator (8005), allow time for the coolant to flow through the radiator tubes to fill both tanks.


Close radiator draincock and install cylinder block drain plug.

Fill the cooling system with a 50/50 ethylene glycol and water mixture. Allow several minutes for trapped air to escape (bubble out) and for coolant mixture to flow through the radiator.

Install radiator cap to pressure relief position by installing radiator cap to fully installed position and then backing off to first stop. This will allow any air to escape, and minimize spillage.


Slide heater temperature and mode selection levers to maximum heat position.

Start engine and run at fast idle (approximately 2000 rpm) for three to four minutes. Shut engine off.

With engine off, wrap radiator cap with a thick cloth, carefully remove radiator cap and add coolant to bring coolant level up to filler neck seat.

Replace radiator cap to fully installed position. Then, back off to first stop. Operate engine at fast idle until the upper radiator hose (8260) is warm (water thermostat (8575) opens). To check radiator, shut engine off, wrap radiator cap with thick cloth and carefully remove radiator cap. Add coolant if necessary. Replace radiator cap to fully installed position.

Open the small cap on the top of the radiator coolant recovery reservoir. The large cap is for the windshield washer reservoir. NEVER put coolant mixture in windshield washer bottle.

Using a suitable suction gun, remove all coolant from radiator coolant recovery reservoir.

Add 1 liter (1.1 quarts) of 50/50 mixture of ethylene glycol and water to the radiator coolant recovery reservoir. Close the small cap. (or fill between the hot and cold marks - suction gun is optional)


Also, check the level after a few trips. The OHV may need a bit extra coolant because of air issues.

[mark v]

Excellent job. This can also work for the 4.0 SOHC Engine, the Thermostat is almost in the same spot but it uses a plastic housing and an O-Ring to seal instead of a gasket.

I made it a Sticky for all to see and use.

Any questions start a new thread.