The Honda Motor Company part number 94109-18000 designates an 18-millimeter aluminum crush washer engineered specifically for sealing drain and fill plugs on Honda and Acura drivetrains. When servicing the rear differential on an Acura RDX, replacing this exact washer is mandatory to prevent gear oil leaks under high-pressure cornering. This guide is written for DIY Acura RDX owners and independent technicians seeking precise factory specifications for rear differential maintenance.
Key Takeaways
- The 94109-18000 is an 18-millimeter aluminum crush washer required for Acura RDX rear differential drain and fill plugs.
- You must use exactly 2 new washers per fluid service (one for the drain plug, one for the fill plug).
- The factory torque specification for the 18-millimeter differential plugs is 33 lb-ft (44 Nm).
- Always verify whether your RDX utilizes an Open Differential or Super Handling All-Wheel Drive (SH-AWD) before purchasing fluid.
Understanding the 94109-18000 Crush Washer
Crush Washer: A single-use, malleable aluminum ring placed directly between a threaded drain plug and a metal mating surface. When properly torqued, the washer permanently deforms to fill microscopic machining imperfections, creating a reliable, leak-proof seal for high-pressure fluid reservoirs like automotive differentials.
The 94109-18000 washer features an inner diameter of precisely 18 millimeters to match the factory drain and fill bolts found on the Acura RDX rear differential housing. Because aluminum is softer than the steel plug and the cast-iron differential housing, it acts as the sacrificial sealing element. Reusing a flattened washer compromises the seal, leading to fluid loss and catastrophic differential failure.
Acura RDX Rear Differential: Open vs. SH-AWD
The Acura RDX platform utilizes different rear drivetrain configurations depending on the model year and trim level. Identifying your specific system dictates the correct fluid type, though the 94109-18000 crush washer remains constant across both setups. According to the Acura Owners Site, using the incorrect fluid in a SH-AWD system will destroy the internal clutch packs within 5,000 miles.
Fluid Capacity and Specifications
Most Acura RDX rear differentials require 2.1 quarts (2.0 liters) of fluid. Vehicles equipped with an Open Differential or a traditional Limited Slip Differential (LSD) typically require 75W-90 Hypoid Gear Oil. Conversely, models equipped with Super Handling All-Wheel Drive (SH-AWD) require specialized Dual Pump System Fluid II (DPSF-II). Always perform the 15,000-mile severe service interval if you frequently tow or drive in mountainous terrain.
| Drivetrain Feature | Open / Standard LSD | SH-AWD System |
|---|---|---|
| Required Fluid Type | 75W-90 Hypoid Gear Oil | DPSF-II (Dual Pump System Fluid II) |
| Standard Capacity | 2.1 Quarts (2.0 Liters) | 2.1 Quarts (2.0 Liters) |
| Drain Plug Washer | 94109-18000 (18mm) | 94109-18000 (18mm) |
| Fill Plug Washer | 94109-18000 (18mm) | 94109-18000 (18mm) |
Step-by-Step Rear Differential Service Guide
Executing a rear differential fluid change requires precision and the correct replacement hardware. Sourcing OEM components from suppliers like Acura Parts Wholesale ensures the aluminum alloy meets factory yielding specifications.
Required Tools and Parts Checklist
- 2 x OEM 94109-18000 Crush Washers (18mm)
- 3 Quarts of DPSF-II or 75W-90 Hypoid Gear Oil (verify application)
- 3/8-inch drive ratchet with 17mm or 3/8-inch square drain plug socket (verify plug style)
- Torque wrench calibrated to 33 lb-ft (44 Nm)
- Fluid transfer pump and drain pan
Drain and Fill Procedure
- Level the Acura RDX on jack stands or a lift to ensure accurate fluid filling.
- Remove the upper fill plug first. This prevents a scenario where the differential drains but the fill plug is seized.
- Remove the lower drain plug and allow the fluid to drain completely into the catch pan for 15 minutes.
- Clean the magnetic tip of the drain plug to remove accumulated metallic particulates.
- Install a new 94109-18000 crush washer on the drain plug and torque to 33 lb-ft (44 Nm).
- Use a transfer pump to fill the differential through the upper hole until fluid reaches the bottom thread of the fill port.
- Install a second new 94109-18000 crush washer on the fill plug and torque to 33 lb-ft (44 Nm).
Frequently Asked Questions
Can I reuse the Honda 94109-18000 crush washer on my Acura RDX?
No. Once the aluminum washer has been compressed to 33 lb-ft of torque, it work-hardens and loses its malleability. Reusing it will result in an incomplete seal and subsequent gear oil leaks onto the exhaust or rear subframe.
What is the exact torque specification for the Acura RDX rear differential drain plug?
The factory service manual dictates a torque specification of 33 lb-ft (44 Nm) for the 18-millimeter drain and fill plugs. Over-torquing can strip the threads in the aluminum or cast-iron housing, requiring a costly differential replacement.
How many 94109-18000 washers are required for a complete RDX rear differential service?
You must purchase exactly 2 washers for a single service event. One washer seals the lower drain plug, and the second washer seals the upper fill plug.
Conclusion
Replacing the 94109-18000 crush washer is a non-negotiable step for maintaining a leak-free Acura RDX rear differential. Your next step is to order two OEM washers and the correct factory fluid before lifting the vehicle, ensuring you can complete the service in a single session without leaving the differential drained.
