When I turn off the engine, radiator blower stays on forever and never stop

check ,remove and replace the coolant fan relay

This is a 2 speed system that utilizes 3 different relays. Remove them one at a time until the fan shuts off.

This is an electric fan that is turned on by a temerature sensor and relay. It is an eleven year old car so the relay or sensor is most likely not working. the right answer is to replace them. The cheap and dirty answer is find the wire that is powering the fan and put a switch on it so you can shut it off and on. Run it up to under the dash somewhere. Use a larger wire than the one you are cutting into because of the distance to the dash. This would destroy your resale value but get you through till the old car finally dies.

No, this is an electric fan controlled by the Engine Control Module that relies on inputs from the engine coolant temp sensor and A/C controls. They are only controlled with the key on so the sensor theory would not apply. These fans are getting power from a full time source in the relay.