Finally had a nice day that wasn't really cold and windy and was able to change the thermostat and temperature sensor today. The thermostat cover was in the way of access to the sensor, so since it had to be removed, I changed the thermostat too. The replacement thermostat was Motorcraft (as was the one removed), and the sensor was NAPA (replacing a Motorcraft sensor).
To get to both requires removing the cover that says "4.0 SOHC", the duct between the air-filter housing, and the throttle body. Then I removed the throttle body after disconnecting the cruise-control and throttle cables. That was as good as I was going to get for access. The flange on the intake manifold was still above the work area, but there was enough room to work.
Of course, the coolant had to be drained. It was in excellent condition, as I expected, because it had been in the truck only about 16,000 miles (26,000 km), so it was reused.
A 3–pound maul with a block of wood was necessary to break loose the thermostat cover (Simmons aftermarket) and the old thermostat. The old one was closed when I removed it, which surprised me, because I thought it might have been stuck open. The sensor was definitely the culprit with the gauge indicating colder than normal, but I suspect the thermostat was opening too soon as well since the heater was warming the cabin, but not as hot as usual. The new one was checked in a pot of boiling water and opened as it was supposed to.
The sensor was a pain to replace, but I got it installed and the retaining clip in place. You will need some of the long heavy needle-nose pliers for this, and lubricating the sensor O-ring with coolant is a great idea. Fortunately, this truck is not like most of the older ones with the V-6 with two sensors, one of which requires removing the intake manifold for access.
About 2+ gallons of coolant had come out. With the thermostat still out after installing the sensor, I used a funnel and filled the engine block with coolant at the housing. After the coolant level reached the housing from inside, I finished installing the new thermostat and put everything back together. I ran the truck for about 45 minutes, and all but about a quart of coolant went back in. That last quart went into the overflow tank.
The temperature gauge is back where it should read, steady on halfway between H and C instead of about a quarter of the way.
By the way, as we've discussed before about other types of work, the Haynes manual is useless for this procedure. That manual indicates that the sensor should screw in. It doesn't on the later trucks, and contrary to the manual, removing the throttle body and the thermostat cover is necessary to get to the one sensor.
While everything was apart, I wiped clean the throttle body and plate with a shop towel soaked with cleaner.
The truck really seems to run a bit better. After finishing, I treated it to a good car wash to get the salt off from previous winter storms before the latest arrives on Sunday evening. Getting the engine running at the proper temperature was also necessary because of extreme (for this area) cold forecast for Monday–Wednesday.
This is a long post, but some of you might find the info useful, I hope.
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