I have started flushing the cooling system/radiator on my 79 eldorado, and after the first drain I filled up the radiator with tap water and turned on the car and noticed that the fan was on, and it has been cool here and I haven't had the car on since yesterday evening.

I'm wondering if the fan should come on right away, or wait until the engine reaches a certain temperature?

Maybe there is a bad thermostat?

 

just an update - flush done, followed this site and procedure except added an extra flush of tap water:

http://www.techguys.ca/howto/coolant_flush.html

felt good to get it done, now I will gradually start trouble shooting things lol not sure where to start, might work on adjusting the drum brakes in the back first then get to the climate control not working/fan running thing.