OK, I got 2 fan clutches from the salvage yard, both seem to be in good shape. I have tested both of them with the same results. The tracker runs at the normal temperature (the needle about 3/4 to the mid point) for 10 to 15 miles, then slowly creeps to the mid point and a little beyond. This is not the normal way the tracker ran in the past. Also if I put it under load, going uphill, it goes even higher.
I took temperature readings after my last run, parking the Tracker and letting it idle. Here are the results. Top of thermostat housing, 200F, bottom hose, 195F, top of radiator, 187F, radiator cap, 160F, water pump, 197F. I have no real idea what these numbers mean. I know the thermostat is supposed open @ 180F, so I'm guessing the coolant shouldn't get much hotter.
Some interesting things I noticed, when I slowed down to make a sharp turn then sped up, the temp gauge fell way back (almost to the 1/4 mark) every time I pushed in the clutch and up shifted. When I reached 5th gear, the needle was back at just past the midpoint. This didn't happen if I just pushed in the clutch while driving or when I down shifted. I took a stick and slowly pushed it into the fan, I was able to stop the fan with very little resistance, in fact I think I could have done it with my hand and it probably wouldn't have hurt me.
The overflow tank was filled to about 1/2 inch below the full line when the engine was cold, and about 1/2 inch above the full line when I parked and took the temp readings.
Cruising the internet, I've learned more then I've ever wanted to know about thermally activated fan clutches, they are often under filled, from the factory with the silicone oil that makes them work. You can put more oil in the clutch, but the pictures didn't match mine so I'm not game to try that. You can't bench test them without some sophisticated equipment (the clutches work on both centrifugal force and temperature.
I am hesitant to purchase a new clutch, unless I am absolutely sure the ones I have are bad. I'm wondering if I should replace the temp gauge or sensor, after the strange needle jumping as I up shifted.
I open to any and all suggestions.