How to replace a serpentine belt on a passenger car? Follow a set order: check the old belt and the tensioner, remove the belt, fit the new one, and check the result. It covers passenger cars with one accessory belt and an automatic tensioner, and the checks before and after.
Access and routing vary, so confirm both in the vehicle’s service information before you start. A car with no automatic tensioner is a different job: that belt is designed to stretch onto the pulleys (Brake & Frontend tech tip on a squealing serpentine belt).
Key Takeaways
- Replace the belt if the ribs are rounded, flat, spider-web cracked, missing, frayed, or glossy.
- If a wear gauge lies flat on the rib tops, the belt is worn. A gap means it can stay in service.
- Photograph the belt path if the routing diagram is missing or unreadable.
- Flutter along the longest run points to the belt or the tensioner; a jerky tensioner arm points to the tensioner.
- Match the original belt length. Indicator marks in the correct position confirm it.
Table of Contents
- Check the old belt first
- Tools, safety and the routing diagram
- Check the tensioner and pulleys before fitting the belt
- How to remove the old serpentine belt
- How to fit the new serpentine belt
- Check the job before you drive
- When to leave it to a shop
- FAQ
- About Longyi Rubber Products Factory
Check the old belt first
Check the belt before you replace it. Replace it if the ribs are rounded over or flattened, if there is spider-web cracking, if rib pieces are missing or frayed, or if the smooth side is glossy or the belt is glazed (Family Handyman’s serpentine belt replacement guide).
Set a wear gauge perpendicular to the ribs with its teeth in the grooves. If the tool lies flat on the rib tops, the belt is worn and needs replacing. A gap under the tool means the belt can stay in service (Dorman Shop Press on serpentine belt wear gauges).
Depending on driving conditions and quality, EPDM belts can last between 50,000 and 100,000 miles, and older neoprene accessory belts typically last about 40,000 miles. One technician quoted by Family Handyman’s serpentine belt replacement guide advises checking belts every three months or every oil change.
Drivers call it the AC belt, the power steering belt or, on older cars, the fan belt. It drives the water pump, air conditioning compressor, power steering pump and alternator, and on older cars the engine cooling fan (Family Handyman’s serpentine belt replacement guide).
See signs of a bad serpentine belt. The belt is also called a multi-V or poly-V belt (multi-V and serpentine belt names).
Tools, safety and the routing diagram
Make sure the engine is off and cool. Put on eye protection and gloves (Family Handyman’s serpentine belt replacement guide).
- A serpentine belt replacement tool releases the tensioner. A belt placement tool helps put the belt on. Ordinary hand tools can do the job, but space around belt-driven accessories can be tight.
- Find the routing diagram, usually under the hood or in the owner’s manual. If there is none, or you cannot read it, draw the belt’s path or take photos before you start.
The automatic tensioner replaces the old job of adjusting V-belts as they wear, so there is no manual tension setting to make. The belt tension guide covers the automatic tensioner.
Check the tensioner and pulleys before fitting the belt
With the engine running, excessive flutter along the longest run means the belt or the tensioner needs replacing (Tire Review on serpentine belt system inspection). A jerky arm, a vibrating belt, noise, or an arm that moves 1/4 in. or more means the tensioner is bad (Family Handyman’s serpentine belt replacement guide).
Check the indicator mark: a mark outside its limits means a weak or sticking tensioner, or a belt of the wrong length.
With the engine off, the tensioner should swing freely without squeaking, binding, clicking or rattling, and the pulleys should turn smoothly without binding, noise or side-to-side rocking.
Oil, antifreeze or power steering fluid will quickly ruin a new belt. Repair the leak and clean the pulleys and idler surfaces first.
The tensioner is a wear item. Replace it whenever a worn belt is replaced (Dorman Shop Press on serpentine belt wear gauges). Family Handyman’s serpentine belt replacement guide calls it wise to replace the tensioner and idler pulley assemblies with a new belt, and a belt-maker representative quoted by Family Handyman recommends replacing belts, tensioner and idler pulleys at 90,000-mile intervals.
On some vehicles a decoupler pulley wears too, and a failed one causes noise and belt flutter.
How to remove the old serpentine belt
Don’t start serpentine belt removal without the diagram or a photo (Family Handyman’s serpentine belt replacement guide).
- Confirm the routing diagram, or use the photo or the sketch you made.
- Fit the tool on the tensioner and rotate the tensioner to release the tension.
- Slide the belt off a smooth pulley, then take the old belt out.
- Release the tensioner slowly.
- Clean rust, gunk and old belt fragments from the pulley grooves and the idlers.
How to fit the new serpentine belt
Start installing a serpentine belt by checking length. A replacement belt must be the same length as the original: too short, and it may not fit or may run with too much tension; too long, even by an inch or less, and it may slip, make noise and wear prematurely (Brake & Frontend tech tip on a squealing serpentine belt). Compare the code on the new belt with the code on the old one, and check it on the serpentine belt size chart.
- Compare the new belt with the old one. Same length, same number of ribs.
- Rotate the tensioner and wrap the belt around the crankshaft pulley.
- Route it around the grooved pulleys, following the diagram.
- Finish on a rounded, non-grooved roller while the tensioner is still rotated.
- Check that the belt sits squarely in every pulley and matches the diagram.
- Release the tensioner slowly (Family Handyman’s serpentine belt replacement guide).
Some cars have no automatic tensioner and use a belt designed to stretch onto the pulleys. These often need a special tool. Forcing the belt over a pulley can damage it, and the replacement must be the same type and the exact length as the original.
Check the job before you drive
Indicator marks in the correct position confirm the belt length. Also check pulley alignment with a straight edge or a laser alignment tool (Family Handyman’s serpentine belt replacement guide). Poor alignment causes more belt noise than any other fault, plus premature wear, mistracking, rib skipping, edge wear and fraying (Tire Review on serpentine belt system inspection).
Start the engine. Check for vibration or noise, and check that the belt runs in the center of the idlers, rollers and tensioner. If the belt is noisy, see serpentine belt noise.
When to leave it to a shop
Leave the job to a shop if an engine mount or other components must come off to reach the belt, or if the belt is nearly impossible to reach (Family Handyman’s serpentine belt replacement guide).
A worn or damaged serpentine belt that breaks with the engine running can cause engine overheating, loss of power steering and a dead battery, and can cut wires and shear sensors.
LYBELT makes belts to a customer’s code, drawing or size. Send the code or a photo of the belt. See the other automotive belts, including multi-V, poly-V and ribbed V belts for cars.
FAQ
How do you replace a serpentine belt?
Confirm the diagram or a photo, rotate the tensioner, and slide the belt off a smooth pulley. Route the new belt around the crankshaft pulley, then the grooved pulleys, and finish on a smooth roller. Release the tensioner slowly.
What tool do I need to replace a serpentine belt?
A serpentine belt tool releases the tensioner, and a belt placement tool helps put the belt on. Ordinary hand tools can do the job, but space around belt-driven accessories can be tight (Family Handyman’s serpentine belt replacement guide).
Should I replace the tensioner when I replace the belt?
Yes. The tensioner is a wear item, so replace it whenever you replace a worn belt (Dorman Shop Press on serpentine belt wear gauges). A belt-maker representative quoted by Family Handyman recommends replacing belts, tensioner and idler pulleys at 90,000-mile intervals (Family Handyman’s serpentine belt replacement guide).
How long does a serpentine belt last?
EPDM belts can run 50,000 to 100,000 miles and older neoprene belts about 40,000 (Family Handyman’s serpentine belt replacement guide). Mileage alone hides rib wear, so inspect the belt every three months or at each oil change.
What if I cannot find the belt routing diagram?
Look under the hood and in the owner’s manual. If it is missing or unreadable, draw the path or take photos before you start (Family Handyman’s serpentine belt replacement guide).
Why is my new serpentine belt squealing?
Oil, antifreeze or power steering fluid on the ribs will quickly ruin the new belt (Family Handyman’s serpentine belt replacement guide). A belt that is too long, even by an inch or less, may slip and make noise, and poor alignment causes more belt noise than any other fault. Recheck the routing, the alignment and the tensioner, and if the noise continues, work through the belt noise causes before replacing more parts.
Sources
- Brake & Frontend tech tip on a squealing serpentine belt
- Family Handyman's serpentine belt replacement guide
- Dorman Shop Press on serpentine belt wear gauges
- Tire Review on serpentine belt system inspection
Source names appear here only as references. LYBELT is not affiliated with them.
About Longyi Rubber Products Factory
LYBELT is the brand of Longyao County Longyi Rubber Products Factory (General Partnership), based in Longyao County, Xingtai, Hebei, China, and making rubber belts since 1999. The factory holds IATF 16949 and ISO 9001 certification and works from 130+ rubber compounds.
The range covers automotive, industrial, agricultural, ATV/UTV and motorcycle belts. For OEM and ODM orders, belts are made to the customer’s part number, drawing or size, with private label and packaging. Email: luxin@lybelt.com.