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Belt smoking please help

I have a 2004 ford mustang. The alternator went out on my car a week ago and has since been replaced but yesterday when I pulled in my driveway, after exiting my car, I noticed that smoke had followed me up the road and was coming out of the hood. It was coming from a belt on the far left. My car has been knocking when it turns on and my boyfriend and I both diagnosed it as a loose belt bc it wasn’t happening before my alternator was changed but I want to make sure before I buy anything. It has no problem turning on or driving anywhere other than its a bit slower. It’s been suggested that I check my oil to make sure I haven’t been running low but my check engine light hasn’t come on and wouldn’t it if I need oil?

If your check engine light cam on with low oil, the light would flash telling you your engine is now destroyed. There is no “low oil” sensor on the car. Low pressure, yes. That is not your problem.

A belt smoking usually means SOMEthing underhood that should be turning is not turning when the engine is running. That takes little more than a look while the engine is running. The smoke should be coming from a pulley that is no longer turning. Are there NO lights lit up on the dash? If the new alternator failed, and that happens sometimes, there should be a yellow alternator light on if that is the problem.

You didn’t say which engine the car has but both have the power steering pump mounted on that side. A failing pump may smoke the belt. A very loose belt may also smoke but steering would get much heavier in both cases. An idler pulley may have failed and locked up also causing smoke. Start it up and look for smoke from a pulley. Remove the belt, turn every pulley above the crank pulley by hand to check to see IF it turns and if it is rough when it turns. You should find a problem if that is the issue. In any event, you need a new belt.

Agreed with Mustangman and I will add that your first step should be checking the engine oil level. This is something you should do every other week at least. When it comes to motor oil you NEVER wait until a light comes on.

Running “a bit slower” could mean an idler or tensioner pulley is seizing up and knocking or it could be the engine is trying to seize from lack of oil.

You’ve gotten two great suggestions from two very knowledgeable guys. All I can add is not to continue driving the car until you get the problem(s) resolved. If you’re too low on oil or you have a component seizing/seized, continuing to drive the vehicle can only create more damage.