Your car relies on many moving parts working together to run correctly, and while some of those parts are visible underneath the hood, others are not. Two of the most important parts your vehicle relies on are the timing belt and the serpentine belt.
The timing belt is inside your car’s engine and manages your engine intake and exhaust valves by keeping the crankshaft and camshaft in sync. The serpentine belt is visibly outside of the engine and transports manual power to all the engine components, including the alternator and AC compressor.
Want to make sure you fully understand how both belts work? This article will explain the main differences between the belts, what they look like, when you should replace them over time since they both maintain different engine parts, and how much a replacement or a repair could cost if necessary.
Are Timing Belts and Serpentine Belts the Same?
Timing belts and serpentine belts aren’t the same, and the two are completely separate from each other. They are both in different locations under the hood and work for different engine parts.
Here are the primary differences between a timing belt and a serpentine belt:
- Located inside engine
- Opens and closes valves by turning the camshaft
- Short diameter in length
- Has V-shaped teeth
- Lasts between 60,000 to 100,000 miles (96,561 to 160,934 kilometers)
- Located outside engine
- Runs power to engine accessories
- Long length
- Has horizontal teeth
- Lasts between 50,000 to 60,000 miles (80,467 to 96,561 kilometers)
How Does a Timing Belt Work?
The timing belt connects the engine crankshaft to the valves that bring in air and fuel and keeps them in sync with the pistons, so they don’t hit each other.
As each piston in the engine moves down the cylinder, the intake valve controlled by the belt closes, the piston moves up to compress the mixture, which is ignited by a spark plug, pushing the piston back down, and the belt opens the valve again to let out the exhaust.
The timing belt keeps this operation perfectly timed for the engine to run correctly. The belts are made with molded polyurethane or neoprene and must be strong enough to stay intact inside the engine.
Timing Belt vs. Timing Chain
Newer vehicles and engines use lightweight materials to make timing chains instead of belts. Chains don’t require maintenance and usually last the length of the engine itself. Older vehicles, however, still use belts and will still need maintenance and replacement.
How Does a Serpentine Belt Work?
The serpentine belt connects the engine crankshaft to the parts of the engine that maintain the system. It coils itself around the engine accessories and keeps moving to transport power to them all at once.
Serpentine belts constantly rotate when the car is running, using a pulley system with a tensioner to move rotational power when being spun by the engine’s crankshaft.
Serpentine belts are long, black, thin, and made of rubber. They’re called “serpentine” because of how they snake through the engine accessories. They withstand heavy use and very high temperatures most of the time.
Two Belts vs. One Belt
Some older vehicles use multiple serpentine belts instead of one long belt. There’s a higher chance of multiple belts slipping due to lower tension and reduced belt life. The flip side is that if a belt slips or goes bad, it only affects one accessory instead of a single belt affecting all of them.
Most multiple belt systems are older, used on larger vehicles, and consume more space under the hood.
What Happens When the Timing or Serpentine Belts Fail?
When the timing or serpentine belt fails, vital engine components quit working. A failing timing belt can cause the pistons, valves, and cylinder heads to go out of sync and collide. Failing serpentine belts cause all the engine accessories to lose power, which will cause the engine to overheat.
Timing belts are much more expensive because they are inside the engine, and some repair shops wait a whole day for the engine to cool down before opening it for any work, even if to replace a worn belt.
Serpentine belts are far less expensive repairs because the part is easily located on the engine and isn’t costly to buy from a parts store. It also doesn’t require a complete engine cool down for replacement and is considered a faster repair job.
When Should I Replace My Timing Belt?
You should replace your timing belt between 60,000 to 100,000 miles (96,561 to 160,934 kilometers) or when your check engine light comes on due to its damage.
Delaying the repair or replacement of a timing belt can be increasingly costly. It could lead to broken or bent valves, damage to cylinder heads and camshafts, piston-cylinder wall damage, or total engine failure.
Here’s a list of signs that it might be time to replace your timing belt:
- Starter issues
- Squealing and rubbing noises
- Engine ticking noise
- A decrease in engine power
- Shaking or vibrating
- Oil leak
Let’s examine these symptoms closer:
If your engine is having trouble starting, it could indicate that the timing belt is out of sync with the valves and pistons and won’t move properly.
That said, timing belts tend to break when the engine is running, and there are a variety of reasons that your car might not start. If your car isn’t starting, it’s more than likely due to something other than the timing belt.
Squealing and Rubbing Noises
This is a common symptom of worn engine belts. If your timing belt is wearing down, the grooves in the belt could make uncomfortable noises by rubbing against the engine during operation. The sound will usually be high-pitched and quite noticeable.
Engine Ticking Noise
A ticking noise under the hood could signify an out-of-sync piston hitting a valve at the wrong time or something else wrong with the camshaft system. Ticking noises in the engine are closely related to oil pressure as well, so if you hear this sound consistently, it’s best to get it checked out.
A worn belt that’s out of sync can cause the engine to overheat, further damaging the engine and its components. It’s not wise to drive on an engine that is overheating, and you won’t be able to for long. While overheating is not always a timing belt issue, you should always take it very seriously.
A Decrease in Engine Power
If your engine is misfiring or has a sour air/fuel mixture, it could be a sign of an out-of-sync system that will cause your engine to run less efficiently. Newer cars sometimes have a warning system to indicate that your engine is running at a reduced power.
Shaking or Vibrating
If your engine is shaking or vibrating the car, it could result from the timing belt wearing down or coming off its tracks. If you notice any abnormal vibrations in the vehicle, it’s best to get it checked out immediately before the timing belt slips off or breaks completely.
An oil leak can cause a timing belt to slip off its track if the oil gets in between the teeth of the belt.
Oil leaks can also reduce oil pressure, and oil pressure is essential for keeping tension on the timing belt. A severe oil leak could ultimately cause the timing belt to come loose.
When Should I Replace My Serpentine Belt?
You should replace your serpentine belt between 60,000 to 100,000 miles (96,561 to 160,934 kilometers). Due to the simplicity and low cost of the repairs, serpentine belts are often replaced during routine maintenance before it becomes urgent.
It’s best to replace your serpentine belt as part of your car’s scheduled maintenance, even if it doesn’t look damaged. Timely replacement will avoid the belt breaking while on the road, which could leave you stranded otherwise and become a much more costly situation.
Here’s a list of signs it might be time to replace your serpentine belt:
- Performance loss
- Chirping or squealing sound
- Cracking, glazing, or fraying on the belt itself
Let’s further examine these signs:
Serpentine belt failure can cause your engine to overheat or your air conditioning and power steering system to work improperly or stop working altogether. Your car battery might also fail to recharge if the alternator is affected. If you notice a general loss of performance, you would want to have your vehicle inspected.
Chirping or Squealing Sound
A persistent chirping or squealing sound from under the hood could signify a failing serpentine belt. The sound can also be louder when starting the engine, accelerating, or making a U-turn. Generally, this is more common for serpentine belts than it is for timing belts.
Cracking, Glazing, or Fraying on the Belt Itself
Visible signs of wear and tear on your serpentine belt when physically checking it are a telltale sign you need to replace it very soon. Given that your serpentine belt is easily visible, you should be able to identify signs of wear on your own.
How Much Does It Cost To Replace These Belts?
Timing belt replacements can cost between $500 to $1000 on average if they are only damaged and not broken, but a broken timing belt can cost more than $2000 to replace. Serpentine belts only cost $70 to $200 to replace on average.
In every repair case, costs can be less or more expensive depending on the make and model of your car and the pricing and location of the repair shop itself.
Timing belts and serpentine belts serve your car’s engine in very different ways.
If you maintain regular maintenance on your vehicle and get your belts replaced when recommended, you will avoid trouble on the road.
If you have to replace your timing or serpentine belt immediately, don’t hesitate, or else it will cost you more money to repair or replace them the longer you wait, and your engine might not survive the subsequent damage caused.