fan runs continuously

Sometimes you need to reset the SMC more than once for it to take effect.

1. Shut down the computer.
2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
4. Release all the keys and the power button at the same time.
5. Press the power button to turn on the computer.
   Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.

Reset the PRAM

1. Shut down your Mac.
2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.

Run the Apple Hardware Test to see if it reports any errors Using Apple Hardware Test

Maybe dust bunnies set up shop within the confines of the MacBook's

ventilation passageways, & if so, that may affect the air cooling ability.

If you decide to look into it more directly, use caution if you choose to

go there and follow those online guides or videos, as they are not exact

and may omit tedious small wire connections that can be easily broken

yet difficult to repair, as part of the overall access situation in MacBooks.

Good luck & happy computing! 🙂