How do you loosen the tensioner to replace the serpentine belt in a 1998 Grand Prix?

. I bought the pay-the-deposit-for-the free-tool-for-these-sidewise-engine-tensioners from Advanced auto. It WORKS. It's skinny enough to fit in there. Cost is under $30.00 and it prevents a lot of air from turning blue. You can get a full refund, or, as I did, keep the tool for the next time. BTW, thanks from me to the prior poster who settled the question in my mind about lifting the engine. And just wait until you have to replace the timing gear cover gasket... That's a RIOT.

-TRP3141592

Use a big socket wrench/breaker bar and the correct socket/bit. Some tensioner pulleys use sockets, others torx bits, and some just use a 3/8 square hole.

The other answer is correct as well, but on my 3.1 litre the tensioner pulley is attached to an arm and the bolt comes through from the back side which makes it impossible to reach with a socket. What I use on mine is a crescent wrench and adjust it to fit the width of the arm the pulley is attached to. This arm is square and the wrench slides on perfectly and then I just pull the wrench up. You can also use an appropriately sized wrench but I don't know exactly what size it is.

Tom

On my 3.8, I used a breaker bar and socket to release the tension and then fit the belt on.