What size wrench do I need to replace a serpentine belt?
Most engines use a 14 mm or 15 mm bolt head on the tensioner, but sizes vary by make and model. Always confirm the exact bolt size from your vehicle’s service manual or a trusted online resource for your engine code.
The rest of this article explains how to identify the exact size for your vehicle, and the tools you’ll typically need to replace a serpentine belt safely and efficiently.
Common belt tensioner bolt sizes
Here are the bolt head sizes you may encounter on serpentine belt tensioners. The exact size depends on the engine, so verify before you work.
- 10 mm
- 12 mm
- 13 mm
- 14 mm
- 15 mm
- 17 mm
Knowing the bolt head size helps you select the right socket or wrench before you begin.
Drive sizes and tool types
In addition to bolt head size, the drive size of your ratchet or breaker bar matters for access and leverage. Common choices include:
- 3/8-inch drive socket or ratchet (most common for passenger cars)
- 1/2-inch drive for heavier-duty tensioners or high-torque engines
- Specialty belt-tensioner tools or adapters that fit specific models
Having the right drive size helps you safely release tension without slipping or rounding the bolt.
How to determine the exact size for your vehicle
To avoid using the wrong size, check these resources that are specific to your car:
- Vehicle owner’s manual or service manual—look up the tensioner bolt size or the tensioner model.
- Under-hood belt routing diagram or sticker—sometimes lists the correct bolt size or tensioner part number.
- VIN-based lookup on the manufacturer’s site or a reputable parts retailer—search by year, make, model, and engine code.
- Ask a professional or parts counter staff with your engine code if you’re uncertain.
Having the exact size saves time and reduces the risk of damaging bolts, the tensioner, or other components during replacement.
Summary
There is no single universal wrench size for replacing a serpentine belt. In practice, many engines use a 14 mm or 15 mm bolt head, but you may encounter 10–12–13–17 mm variants, and the appropriate drive size is usually 3/8-inch or 1/2-inch for the ratchet, with some models requiring specialized belt-tensioner tools. Always verify with your vehicle’s manual or a reliable engine-specific resource keyed to your VIN and engine code, and keep a belt routing diagram on hand during the replacement.
