In an engine compartment, loose belts will:
Not turn the water pump and/or fan properly, causing the engine to overheat.
Make the engine run more efficiently.
Make the fan run too much, causing the engine to run too coolly.
Last longer than tight belts.
Be sure to check the tightness of the belts in your engine compartment. Loose belts will not turn the water pump and/or fan properly, which can lead the engine overheating.