Squeaking Serpentine Belt - 90 Buick Century?

Quite Frankly, You need to straighten out this problem.

Let it run idle for 15 minutes. If it continues. Head to the repair shop

or back to the repair shop.

Belt assembly?

Well, usually, a squeaking is either a dry pulley, or more commonly the belt slipping on a pulley. Even my newer vehicle squeaks when its started cold, but goes away very quickly.

I would replace the belt (Goodyear Gatorback is the best in my opinion), or try to figure out which pulley is squeaking. This can usually be accomplished by removing the belt and turning pulleys by hand with the engine off.

90 Buick Century

On most cars, new belts need to be readjusted after a day or two. However, I believe your Century has a belt tensioner. If it is worn out, it doesn't keep the belt as tight as required, and would need to be replaced.

Check your plugs, is there fuel on them? Check your spark at the plugs! Does the engine sound funny when you try to start it? If the timing belt broke, the engine will spin over MUCH faster than normal and will sound like there is no resistance to it …which there is not anymore if the belt broke. I know that the belt that you replaced is not related to the timing belt, but it could be that when the drive belt broke it also broke the timing belt, or caused the chain to jump a tooth on the gear. If the timing if off to much it will not start! Good luck!

Exactly, did you replace the belt tensioner ? If not the belt is way too loose.

You need to look at belt tensioner bearing. Also check new alternator to make sure it aligns with the belt. The pulley could be out of alignment

did you replace the belt and the belt tensioner