I have bought a used 2000 Nissan Altima. Sometimes when I drive the car for a long time (more than 30 minutes), I notice that the cooling fan under the hood runs even after switching off the engine.
It always takes an extra 1-2 minutes after which the fan turns itself off. I checked the engine temperature and it's not getting very hot. Is there any problem with the car?
Probably not...your Altima's 2.4-liter engine uses two electric coolant fans mounted in front of the radiator. The fans are controlled by the powertrain control module (PCM). The PCM turns the fans on & off based on several data inputs. One is the coolant temperature reading from a sensor mounted on the engine. But it also looks at the air conditioning being on or off, a high pressure signal from the air conditioning compressor, engine speed, vehicle speed, and whether the ignition is turned on or off.
If the engine's coolant temperature is above 205 degrees F (96 degrees C) when the engine is shutdown, the coolant fans will continue to run for a maximum of 120 seconds. Typically the coolant fans come on in traffic when there's minimal airflow through the radiator. They're not needed as much on the highway because of the air rushing through the grill at higher vehicle speeds.
Here's a quick test you can perform yourself. Always be sure the coolant system is full, and next time you park the car with the engine fully warmed up and the air conditioning off, let the engine idle and listen to the coolant fan operation. It should come on when the coolant temperature reaches a certain point, and go off after a minute or two of operation as the temperature drops. This tells us that the fans and the coolant system, in conjunction, are able to effectively reduce coolant temperature to a safe level.
If the fans do not shut off, there may be a problem with coolant system operation. If you still have doubts, have it checked out at a qualified repair shop.