2018 Toyota Highlander Transmission & Axle Gear Ratios

Transmission gear ratios

The 2018 Toyota Highlander was offered with two primary transmission options, depending on the engine and drivetrain configuration:

U660E 6-speed Automatic (2.7L 4-cylinder FWD)

U151E 5-speed Automatic (3.5L V6 FWD/AWD)

Available axle ratios

The 2018 Toyota Highlander offered a variety of axle ratios to complement its engine and transmission choices, influencing both fuel economy and towing capability.

How to identify your axle ratio

Identifying the axle ratio on your 2018 Toyota Highlander is relatively straightforward, although the method differs slightly from domestic brands like GM or Ford. Toyota generally doesn't use dedicated RPO (Regular Production Option) stickers on the door jamb for axle codes in the same way. Instead, you'll typically find the axle code on a placard or sticker under the hood, or on the driver's side door jamb, which includes the vehicle's VIN, tire pressure information, and sometimes the "C/TR" code (Color/Trim). The last four digits of the "C/TR" code often contain information about the differential.

For a more definitive answer, especially if there's any ambiguity, you can use a Toyota VIN decoder online or consult with a Toyota dealership's parts department. Provide them with your full VIN, and they can tell you the exact axle ratio your vehicle was equipped with from the factory.

Another method is to physically inspect the differential itself. While there might not always be an easily visible tag like on some Ford or Ram trucks, you can sometimes find stamped numbers on the differential housing that a knowledgeable mechanic can decipher.

Towing vs MPG impact

The axle ratio plays a significant role in determining a vehicle's balance between towing capability and fuel economy. It essentially dictates how many times the driveshaft rotates for every single rotation of the wheels.

• Numerically Lower Ratio (e.g., 3.000): A numerically lower axle ratio means the engine doesn't have to work as hard to maintain cruising speed. This translates to better fuel economy because the engine operates at lower RPMs. However, it also means less torque multiplication at the wheels, making it less ideal for heavy towing. The vehicle will feel like it has less "grunt" off the line or when pulling a heavy load up an incline.

• Numerically Higher Ratio (e.g., 4.156): Conversely, a numerically higher axle ratio allows the engine to rev higher for a given wheel speed. This provides more torque multiplication to the wheels, significantly improving towing capacity and off-the-line acceleration. The trade-off is often reduced fuel economy at highway speeds, as the engine will be working at higher RPMs to maintain the same speed.

For the 2018 Toyota Highlander, the 3.000 axle ratio paired with the V6 AWD system is geared more towards fuel efficiency for a vehicle of its size, while the 4.156 ratio on the 4-cylinder FWD model helps to compensate for the smaller engine's power output, providing adequate performance for daily driving and light hauling.

Common issues

While the Toyota Highlander is known for its reliability, like any mechanical component, differentials can experience issues over time. Some common concerns that can arise include:

• Ring and Pinion Whine: This is often a tell-tale sign of wear or improper setup within the differential. A high-pitched whine that changes with vehicle speed and/or throttle input can indicate worn gear teeth, incorrect gear mesh, or improper backlash.

• Carrier Bearing Wear: The carrier bearings support the differential carrier, which houses the ring gear and spider gears. Worn carrier bearings can cause a low-pitched howl or rumble that intensifies with speed, often noticeable in turns or under acceleration.

• Limited-Slip Clutch Wear (if equipped): Some differentials, particularly those designed for enhanced traction, might incorporate limited-slip mechanisms with clutch packs. Over time, these clutch packs can wear out, leading to a loss of the limited-slip function, clunking noises during turns, or shuddering from the rear end.

Regular differential fluid changes using the manufacturer-specified fluid are crucial for preventing these issues and extending the life of your Highlander's differential.

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