Next time you work with a drive belt, Car Pulley Belt timing belt, or timing chain, you’ll likely have to loosen a tensioner pulley to eliminate it. Following these general recommendations and specific instructions from your own owners manual or repair manual, your belt or chain will function for the life of your car.

Toyota and various other timing belt tensioners are loosened by simply removing them from the engine. You need to slowly compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are nearly always located in the timing case, mostly on vehicles with timing chains, while some are used in combination with timing belts. Hydraulic tensioners are powered by oil pressure from the engine essential oil pump and may press on a tensioner pulley (timing belts) or pressure slipper (timing chain). You will likely need the entire year, make, and model details, and you may have to use special tools for this type of tensioner pulley.
Typically, a hydraulic tensioner must be “reset” and locked after removing it from the engine. Take away the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are set up and aligned.

The spring maintains tension, as the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping teeth and maintains drive belts from slipping and producing noise. To loosen a drive belt springtime tensioner pulley, refer 1st to the restoration manual or owners manual’s specific season, make, and model information.
You may need a special tool, but many spring tensioners have a square hole, for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the correct tool, release pressure on the belt. You will have to hold some spring tensioners while slipping on a fresh belt. Others may have a locking mechanism, like a hole for a locking pin or hex important.

To loosen an NAI tensioner, loosen the locking nut or bolt, after that cool off the tensioner screw. Push the pulley toward the various other pulleys or add-ons, loosening the belt.
Spring tensioner pulleys, since the name implies, use a spring to hold tension upon the belt. Most, if not absolutely all, springtime tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and expensive but don’t require adjustments and are less prone to user error.