On a 2002 Siennia Toyota my fan belt keeps squeaking... how tight can I tighten it?
It is often the pulley(s) squeaking. I'm thinking there is a tensioner on that vehicle that automatically adjusts the belt tension.
Scotty has a YouTube video that might help: "The Secret to Fix a Squeaky Belt in Your Car".
If you spray some water and the squeaky noise goes away, it is time to change the belt.
If not, then the pulleys need to be fixed.