2018 Chevrolet Suburban: Transmission Fluid & Service

Quick answer

• Transmission make/model: GM 6L80 (RPO MYC) or GM 8L90 (RPO M5U)
• OEM fluid spec: DEXRON VI (6L80) or DEXRON HP (8L90)
• Drain & fill capacity: Approximately 6.0 quarts (6L80) or 8.5 quarts (8L90)
• Full overhaul capacity: 12.4 quarts (6L80) or 11.4 quarts (8L90)
• Filter OEM part number: Verify with dealer or service manual.
• Recommended service interval: 45,000 miles (severe service)

Fluid type explained

The 2018 Chevrolet Suburban was available with two different automatic transmissions: the 6-speed 6L80 and the 8-speed 8L90. It is critical to use the correct fluid for your specific transmission.

The 6L80 transmission uses DEXRON VI automatic transmission fluid (ATF). This is a synthetic fluid that was introduced in 2005 and offers improved performance and durability over previous DEXRON fluids. It provides better oxidation resistance, shear stability, and anti-wear protection.

The 8L90 transmission requires DEXRON HP (High Performance) automatic transmission fluid. This is a low-viscosity synthetic fluid that was specifically developed for GM's 8- and 10-speed transmissions. It is not interchangeable with DEXRON VI. Using the wrong fluid can lead to shift quality issues and, eventually, transmission damage.

Service procedure

A transmission service can be performed in two ways: a drain and fill or a full fluid exchange.

A drain and fill is the more traditional method and involves removing the transmission pan to drain the fluid, replacing the filter, and refilling the transmission with fresh fluid. This method typically replaces about half of the total fluid in the transmission.

A full fluid exchange uses a machine to pump out all of the old fluid while simultaneously adding new fluid. This method replaces nearly 100% of the fluid and is the preferred method for many shops.

Service interval

For the 2018 Chevrolet Suburban, the recommended service interval for the automatic transmission is every 45,000 miles for severe service. Severe service is defined as operating the vehicle in one or more of the following conditions:

• Mainly in heavy city traffic in hot weather
• In hilly or mountainous terrain
• When frequently towing a trailer
• When used for high-speed or competitive driving

If you do not operate your vehicle under any of these conditions, you may be able to go longer between services. However, it is always best to consult your owner's manual or a trusted PURE Auto Repair technician for their recommendation.

Common transmission problems

The 6L80 and 8L90 transmissions are generally reliable, but they are not without their problems. Some of the most common issues include:

• Torque converter failure: This is the most common problem with the 6L80 and can cause a variety of symptoms, including shuddering, slipping, and overheating.
• Shift solenoids: The shift solenoids are responsible for controlling the flow of fluid in the transmission. If they fail, it can cause a variety of shifting problems.
• Valve body issues: The valve body is the hydraulic control center of the transmission. If it becomes warped or damaged, it can cause a variety of shifting problems.
• 8L90 shift quality issues: Some owners have complained of harsh or erratic shifting with the 8L90 transmission. In many cases, this can be resolved with a software update. However, in some cases, it may require a hardware repair.

If you are experiencing any of these problems with your 2018 Chevrolet Suburban, it is important to have it diagnosed and repaired by a qualified technician as soon as possible.

Find a trusted shop on Repairius.