Should You Replace Your Car’s Serpentine Belt When Replacing The Alternator?

The short answer here is that yes — in most cases — you should replace your car’s serpentine belt when replacing the alternator. The issue isn’t so much that the two components are part of the same system, although they are. There’s a well-known wrenching principle at work here. 

Consider a situation where you need to replace a worn or broken part, but the only way to access that component is by removing another part that’s still operational. Many times, it makes sense to go ahead and replace the first part, since you’ve already gone to the effort to remove it. That’s exactly what’s going on under the hood of most internal-combustion cars, which do, in fact, require you to remove the serpentine belt to remove the alternator. 

There are exceptions, of course. The basic job of an alternator and serpentine belt is to change the mechanical power of the engine into electricity, which is then used to run the vehicle’s electric systems and keep the battery charged. So-called mild hybrids rely on a different setup, with an integrated starter generator, to do the same thing. However, while you don’t have to worry about having an alternator go bad or snapping a belt with a mild hybrid, they can be a lot more expensive to repair. Just replacing a new mild hybrid battery can cost $1,500 or more.

The only electricity an internal combustion engine really needs is the spark from the spark plugs. They can even be started by hand, and they were when people had to crank them to get them moving — the electrical starter didn’t first appear until the 1912 Cadillac Model 30, also was the first car with electric headlights. As cars began adding electrical accessories, automakers developed generator systems to meet their needs, but these tended to be unreliable, inefficient, and not very good at making electricity at low engine speeds.

That all changed with Chrysler’s 1960 Valiant. It was the first car with a modern alternator as standard equipment — and also the first car with the Slant 6 motor, an oddly tilted engine that refused to die. As for the alternator, it had two key parts: a rotor that’s basically in a doughnut shape and spun by engine power, and a stator that’s wrapped in wire and remains stationary in the center of the doughnut. As the doughnut spins, the magic of electromagnetism creates electricity, which is then used for the car’s accessories and helps keep the battery topped up.

What directly spins the alternator’s rotor in the first place? That would be the serpentine belt, which is driven by a pulley connected to the crankshaft. The belt then snakes around a variety of other pulleys to provide power not only to the alternator, but also things like the power steering system, air-conditioning compressor, and water pump.

Let’s review for a sec: A serpentine belt plays a huge role when you’re driving, not only helping with comfort features like the AC, but also by running the water pump to prevent your engine from overheating. If that happens, you could be looking at permanent engine damage. Nor is it safe to drive if your power steering — also run by the serpentine belt — suddenly goes out. At that point, you’re trying to wrestle with thousands of pounds of metal — no easy task.

Yet all that and more hinges on a piece of reinforced rubber that can cost under $10 and will usually last only 60,000 to 100,000 miles. When you consider that the typical car today can stay on the road for up to 200,000 miles, and some have broken the seven-figure mark, simple wear and tear is likely to lead to at least one serpentine-belt change in a vehicle’s lifetime.

You can recognize the signs of that wear and tear by listening for squealing/squeaking sounds coming from the engine bay. (But remember, there’s a long list of horrible things you should never use to quiet a noisy engine belt.) In addition, you should be alert to signs of inconsistent electricity production from the alternator, like flickering lights when you first start your car. Don’t forget routine visual inspections, either, to check the belt for cracks, fraying rubber, worn edges, worn grooves on the bottom of the belt, and a shiny look to the top.