First, I've now changed the thermostat again. Different brand than the first one, but they were/are both 198 degree F units.
Your observations and deductions make perfect sense. I have seen the fan stationary even for a good clutch. It always spins. May be not as fast but it spins. Mine certainly does. But as you said you get huge air flow when you start driving anyway. Does it warm up just idling?
It really doesn't warm up much when idling. It always used to. I could fire it up on a cold day, just let it sit and warm up, and the temp gauge would be at the middle fairly fast.
As things are now, if I just start it and let it idle, the gauge comes up to right around the line at the "C". Then, when I drive it, it warms up a bit more, and with this latest (put in today) thermostat, the highest I ever saw the gauge go was maybe a hair over what is shown in that photo we've been plagiarizing in this thread.
The fan will always appear to be spinning. The clutch allows it to slip when the engine is cold and increases engagement when the clutch spring gets warm/hot based on the air temp flowing through the radiator. The fan's job is to help cool the radiator when your not moving. It doesn't really cool the engine block.
It's clear to me that your thermostat is the problem. Overheating can be caused by a multitude of factors. Under-heating is pretty much always your thermostat. Period.
I appreciate both of you guys' information about the fan. I suspect mine is working just fine, then. The fan moves fairly easily when pushed by hand when the engine is cold. It probably just spins somewhat when I first start the car because of the bit of drag it does have at that temperature.
I've had to replace the thermostats in every car I've ever owned (Well, OK, not the VW Bug, but...)
And the symptoms were usually a lot like what I'm seeing with this vehicle. And putting in a new thermostat has always fixed the problem immediately, and positively. So that's why I changed this one right off.
But now, I've put in the 2nd thermostat in as many weeks, and neither one seems to be making any significant difference.
But I need to let this one run for a while, make sure the system is properly burped and fully topped off, etc., but so far, today, it seems just like it was at first, and after putting in the first new thermostat a few weeks ago.
So I bought a new temperature sensor/sender for the thermostat housing. I'll put it on if things continue to act strange. Maybe the thermostats have all been just fine, but the sensor is lying to me. And I'll check the wiring and connectors for the temperature sensor, too, in case it's just a broken (intermittent) wire or a crummy connector.
It was almost up to freezing today, and the sun was shining, so I took that opportunity to swap in the new new thermostat. But it's supposed to snow and get colder in the next couple of days, so I'll have more opportunity to observe the cold weather behavior.
I did, indeed, have the first thermostat installed correctly (wax pellet in, pointy end out - and bleeder valve thing at 12 O'Clock) for what that's worth.
I'll let you all know what happens, and if I swap in the new temperature sensor, too.
Thanks again, everyone.