The insider’s guide to engine belts


Virtually every automotive engine uses rubber belts to power various accessories outside the engine block and critical engine parts inside. The belt that is external to the block is usually called the accessory belt or fan belt. They used to be a single V-shaped belt but today they are serpentine belts that slither around several pulleys. These pulleys typically drive the alternator, AC compressor, power steering pump and water pump. Sometimes this serpentine belt is mounted in the front of the engine but in transverse engines, it’s usually 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 crucial task of connecting the crankshaft at the bottom of the engine to the cam shaft in the cylinder head on top. You should note that many engines have timing chains instead of belts. A key difference between the two is that a timing chain is usually considered a lifetime part that doesn’t require periodic replacement.

Serpentine accessory belts

If your serpentine belt breaks, your vehicle is going to eventually come to a halt. 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. Mopar Genuine Parts, a major Mopar on-line parts site, says that car manuals usually suggest a certain mileage point at which the belt should be replaced.

Replacement costs for serpentine belts also vary but are typically they range from $75 to $150 or so.

Engine timing belts

Now let’s look at the real critical belt: your timing belt. Timing belts are inside your engine and they perform a critical task; they keep the crankshaft and camshafts rotating together in proper timing. On some engines if the timing belt breaks, the pistons may continue to move and in the process. That can add up to real money if it happens, possibly $3,000 or more. Replacing a timing belt is far cheaper, typically running from at least $500 to more than $1,000.

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.


Its best to head off problems before they occur. Be sure to change your engine’s belts according to the schedule that the manufacturer recommends. If you do, you will avoid any surprise expensive repairs as your car ages.


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