🔧 RX350 - Serpentine Belt Replacement

The serpentine belt (drive belt) runs your alternator, A/C compressor, and other accessories. Replacing it when it’s cracked, noisy, or glazed helps prevent a sudden breakdown and charging/overheating issues.

Difficulty Level: Intermediate | Estimated Time: 0.8-1.5 hours

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⚠️ Safety & Precautions

• 🛑 Work on a cool engine; belts and pulleys can burn you when hot.
• 🛑 Keep fingers/clothing away from pulleys; never run the engine with hands near the belt.
• 🛑 Support the RX350 with jack stands if you lift it; never rely on a floor jack alone.
• 🛑 No battery disconnect is required, but keep the key/fob away so nobody starts it.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Mechanic gloves
• Floor jack (rated 3-ton minimum)
• Jack stands (rated 3-ton minimum)
• Wheel chocks
• 21mm socket
• 1/2" breaker bar
• Torque wrench (20-150 ft-lbs range)
• 10mm socket
• Ratchet (3/8")
• Trim clip removal tool
• 14mm wrench
• 19mm wrench
• Flashlight

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Serpentine belt (accessory drive belt) - Qty: 1
• Engine under cover / splash shield clips (as needed) - Qty: 1 set

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📋 Before You Begin

• Park on level ground, shift to Park, and set the parking brake.
• Chock the rear wheels using wheel chocks.
• Find the belt routing diagram (usually on a sticker under the hood). If it’s missing, take a clear photo of the current routing before removing the belt.
• Tip: Draw the routing on paper first.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Raise the right-front corner (recommended for easiest access)

• Use a floor jack (rated 3-ton minimum) at the front right jacking point and lift the RX350.
• Place jack stands (rated 3-ton minimum) and gently lower the vehicle onto the stands.
• Remove the right-front wheel using a 21mm socket and 1/2" breaker bar.

Step 2: Remove the splash shield for belt access

• Remove the fasteners/clips from the right-front splash shield/under cover using a 10mm socket, ratchet (3/8"), and trim clip removal tool.
• Pull the panel(s) back enough to see the belt, tensioner, and lower pulleys.

Step 3: Identify the belt tensioner and the “hex” you’ll turn

• Locate the automatic belt tensioner (spring-loaded arm with a smooth pulley).
• The tensioner arm will have a hex you turn to release tension; on these Toyota/Lexus setups it is commonly 14mm or 19mm.
• A wrench is the hand tool you place on the hex to rotate it.
• Tip: Use a flashlight to confirm hex size.

Step 4: Release belt tension

• Fit a 14mm wrench on the tensioner hex. If it doesn’t fit, use a 19mm wrench.
• Pull the wrench smoothly to rotate the tensioner and loosen the belt (it will feel springy).
• While holding the tensioner rotated, slide the belt off the easiest-to-reach pulley (often the alternator or an upper idler).
• Slowly let the tensioner return to its resting position (don’t let it snap back).

Step 5: Remove the old belt and compare it to the new belt

• Remove the belt fully from all pulleys by hand.
• Compare old vs. new belt length and rib count (the grooves must match).

Step 6: Install the new belt (route it correctly)

• Route the new belt around the pulleys following the under-hood diagram (or your photo).
• Make sure the ribbed side sits in the grooved pulleys and the smooth side rides on smooth pulleys.
• Double-check the belt is fully seated in every pulley groove using a flashlight.
• Tip: Leave the easiest pulley for last.

Step 7: Apply tension and finish seating the belt

• Use the 14mm wrench or 19mm wrench to rotate the tensioner again.
• Slip the belt onto the last pulley, then slowly release the tensioner.
• Inspect every pulley again to confirm the belt ribs are not “one groove off.”

Step 8: Reinstall splash shield and wheel

• Reinstall splash shield/under cover using a trim clip removal tool, 10mm socket, and ratchet (3/8").
• Reinstall the wheel using a 21mm socket.
• Lower the RX350 off the stands using the floor jack (rated 3-ton minimum).
• Tighten lug nuts in a star pattern with a torque wrench: Torque to 103 Nm (76 ft-lbs).

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✅ After Repair

• Start the engine and watch the belt for 20-30 seconds; it should run centered and smooth (no hopping).
• Listen for squeal/chirp. If present, shut off and re-check routing and pulley seating.
• Turn on A/C and headlights to add load and confirm normal operation.
• Recheck the splash shield fasteners after a short test drive.

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💰 DIY vs Shop Cost

Shop Cost: $180-$350 (parts + labor)

DIY Cost: $30-$80 (parts only)

You Save: $100-$270 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 0.8-1.2 hours.

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🎯 Ready to get started?

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