What you need to know about engine belts

Virtually every engine uses rubber belts to rotate accessories and critical engine parts. The most obvious one is the accessory belt. It usually is a serpentine belt that slithers around the pulleys that drive the alternator, air conditioning compressor, power steering pump and water pump. Sometimes this serpentine belt is mounted in the front of the engine, sometimes it is on the side. Serpentine belts need to be replaced when they show wear, such as cracks, fraying or stretching.

Some engines also have a timing belt buried inside. It accomplishes the critical task of connecting the crankshaft on the bottom of the engine to the cylinder head on the top. Many engines have a timing chain instead of a belt. A key difference is a timing chain is usually considered a lifetime part that doesn’t require periodic replacement. A timing belt does require replacement because they wear out.  Generally speaking replacing a timing belt is relatively expensive because of the work it takes just to get to it.

engine belt

Serpentine accessory belts

If either the serpentine belt or timing belt breaks, your vehicle is going to eventually come to a halt. Let’s start with the serpentine accessory belt.  If it breaks, your engine will run for a few minutes but it may start to overheat and the battery may quickly go dead. Though serpentine belts can last more than 100,000 miles, they should be inspected by a mechanic periodically to see if it is worn or has cracks. Consult your owner’s manual or service schedule to find out how frequently it should be inspected. Mullahey Chrysler in Paso Robles, CA, a full service Chrysler, Dodge, Jeep, Ram dealer, says that car manuals usually suggest a certain mileage point at which the belt should be replaced.

Replacement costs for serpentine belts also vary and we’ve seen estimates from less than $75 to more than $150. The best approach is to have it inspected before the recommended interval, and if you decide to have it replaced you will have time to shop around.

Timing belts

Now let’s look at the real critical belt: your timing belt. Timing belts are usually inside your engine and they perform a critical task; they keep the crankshaft and camshafts rotating together in proper sync. Replacing a timing belt is a more involved process and costly procedure, typically running from at least $500 to more than $1,000. Even worse, on some engines if the timing belt breaks, the pistons may continue to move and in the process bend the engine valves that have lost their timing sync. That can add up to real money if it happens, possibly $3,000 or more.

That makes timing belt replacement more critical, but because it is not visible, you can’t easily check it. That is why you should pay close attention to the manufacturer’s recommended replacement schedule for your timing belt. Here, too, recommendations vary. Some Honda V-6 engines call for timing belt replacement at 60,000 miles, for example, but the 1.8-liter four-cylinder used in some Chevrolets lists it at 100,000 miles.


So the best offense is a good defense. Be sure to change your engine’s belts according to the schedule that the manufacture recommends.  If you do, you will avoid any surprise expensive repairs as your car ages.

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