I bought my daughter a 99 monte carlo, I don't know much about cars, but she called me last night and said car stalled on her, then started it back up, (no problem) but then oil was low (no oil light) she put oil in it, we flushed radiator due to it being nasty. ( black ), Now we have the problem there is a loud knocking coming from the motor.. help what could this be. she loves her monte.. and its a very nice car

 

Is the check engine light on? If so, go to Autozone and get them to read the codes.

Loud knocking is typically something bad, like a bent rod, damaged valve, or spun bearing. If it's just kind of a tick, it's probably just the fuel rail.

 

^Click on pic to see video ^

does it sound like this? if so it's likly a rod knock

This was my sisters buick rendezvous with a 3.4(same family as 3.1) that had a prun bearing in the #4 rod,

 

How low on oil was it? If you added three or more quarts then it is probably a rod knock and that means an engine rebuild or replacement. I wish for you the best of luck with your Monte. Welcome to the MCF.

 

Welcome to the site. It looks like a nice car.