I've had my car sitting for quite some time due to an interior overhaul and prep for paint work, so today I decided I would let my car idle for a while just to keep everything fresh. About 10 minutes later I shut off my engine and turn the key onto accessory and the secondary fan starts up and keeps running until I turn the ignition off. Anyone know what could be the culprit?

 

AFAIK, that's normal. The water stops circulating when you turn off the engine, therefore the heat gets transferred into stationary coolant which sticks around the sensor in the head, resulting in your fan starting due to a temperature your gauge does not display.

 

That does sound completely logical, except I went to try it out this morning and turned the key to accessory (without turning on the engine prior to yesterday) the fan still started right up

 

Doesn't it have it's own fan switch in the head?
Maybe it is faulty?