I believe my 8A-10884 sending unit has gone wonky.

Key off, the unit reads H (as designed) I then put the key on and it drops to C (as designed). I start the engine - it will stay at C for a bit, then hover just over half for a bit, and then max out at H. It will do this will idling in the driveway over the course of 15-20 minutes. No signs of overheating. The last occurrence was with an ambient air temperature of under 40F.

I've done some research and it appears the aftermarket units available today are generally seen as garbage. I've gone though my hoard of parts and also found and won a lot of used units on an online auction site.

Am I on the right track replacing the sending unit? Is there a way to test the non-aftermarket KS sending units to select one from the hoard to use as a replacement?

 

I've seen this behaviour with no/little water in the system. I'd check that first.

 

This is the schematic for the temperature gauge. There are TWO devices to be concerned with, the sensor (temperature sending unit) and a switch (excess heat unit). Try running from the sensor (single-terminal unit) to the dash gauge, without the switch in the circuit.

 

^ Added the Ford part numbers.

8A-10884 / Obsolete ~ 203 available NOS

8A-10990 / Obsolete ~ 272 available NOS

 

Woke truck up from winter hibernation and ensured the antifreeze was topped off. A short 15 minute drive had the temp very high with 70 degree weather. Stock fan operating as expected. I really want to get this licked...

 

Just to be clear, was the engine temperature actually overheating, or is it just the gauge mis-reading?

 

The engine isn't drastically overheating (emitting steam or looking cherry red), but reads warm and previously has maxed out.

 

Your thread title 8A-10884 is a different sending unit than the above.

8A-10884 is the temperature sending unit, 8A-10990 is the excessive heat indicator sending unit.

 

I believe it is the 8A-10884 - the temp sending unit, not the excessive heat cut out.