Let's distinguish "fan" noises into two separate categories:
1. climate control blower
2. radiator cooling fan
So, #1 is on whenever the car is running. You can barely hear it, it's quiet. It comes on precisely 50 minutes after the car is shut down to clear the AC evaporator. It runs for a few minutes, which is why, on occasion, you'll hear it.
#2 comes on when the engine temperature exceeds a certain value (no idea what that is) and it comes on when the AC is engaged (which is nearly all the time, as defrost uses the AC to dry the air) so that the AC condenser has air flowing over it. Further, it can remain on after the car is shut down, if the engine temperature is too high (again, no idea what that value is).
As long as #2 stops running a few minutes after shutdown, you're OK.
However, a common failure mode for the fan module (which is integral to the fan, and not separately replaceable) is to get stuck in the "ON" position and it will run until your battery dies. In which case, you'll need a new fan, and maybe a new battery.
Two notes:
1. Your temperature gauge is really an idiot light in disguise. It points to the 12 o'clock position as long as the engine temperature is roughly 180-230 degrees. So the engine temperature can vary considerably, but your gauge shows the same value. You really have no idea if the engine is running a bit warmer than usual on a really hot day. That's intentional and reduces service complaints on the car. All manufacturers do it, and a scan gauge that reads actual engine temperature will reveal this to be the case.
2. If you run the battery flat one day, please charge it all the way up using a good battery charger. A jump start is an emergency procedure, useful for getting you back on the road, but it doesn't help your battery. Getting a dead battery back to a reasonable state of charge takes several hours of running the engine. Better to do that with an electronic charger that will bring it all the way back and taper the charge at the end.
Current Fleet:
2016 Tundra Crewmax 4WD 1794
2005 MB S600 (126K, Michelin AS4, HPL 0W40)
2005 MB SL600 (55K Michelin AS4, Mobil 1 0W40)
2004 V70R (143K, six speed M66, HPL 5W40)
2004 XC90 (235K, HPL 0W30 Euro)
2002 V70-XC (295K, HPL 0W30 Euro)
2002 V70-T5 (225K, IPD bars, Bilsteins)
2001 V70-T5 (125K, IPD downpipe, cat back and other mods)
1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)
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