On Mon, 13 Aug 2012 10:56:47 -0700, "Guv Bob"
wrote:

OK, back to the beast again. On the road, temperature is just slightly above mid-range, where it has always been. When stopped with engine idling, the temp slowly increases. If I set for more than a few minutes, it approaches max full scale. When I drive off, it comes back to normal.

Another symptom - that may or may not be normal or related - is when I start up cold, it takes a good 10 minutes to come up to temperature. Other car takes about 2 minutes.

R/R fan clutch -- no change.

First, analyse the problem. It's a Ford (Found On Road Dead).

OK, lets go a little deeper. The engine temperature is fine at road
(highway?) speeds when the engine is working hard. The temperature
rises when the engine idles. Air flow over the engine will not keep
it cool, that's why they have radiators.

I have never encountered an air lock problem, but will admit that
others may have more experience.

This does not sound like a thermostat problem. With a faulty
thermostat I would expect the engine to run at an elevated temperature
while pulling a load, and cool off when idling. A problem I HAVE
encountered is a defective radiator core - the fins had broken free of
the tubes. Again, it would run cool at idle and overheat under load.

The symptoms sound like the fan is not moving enough air - at driving
speeds sufficient air is forced through the radiator to dissipate the
heat, at idle the air isn't moving fast enough. The three possible
causes are a slipping fan belt, a defective fan clutch (which you have
already replaced), or a fan in backwards. If the fan blades are
curved there is only one 'right' way for it to be installed. A friend
made that mistake once - and got the 'Mr. Badwrench' award.

PlainBill