The best option is Dexron VI automatic transmission fluid that meets GM Dexron VI specifications; Dexron VI-H is also an acceptable variant for some service. In practice, use an OEM-approved Dexron VI fluid such as GM/ACDelco Dexron VI.
The 2018 GMC Sierra 1500 is equipped with a GM automatic transmission that generally requires Dexron VI, rather than older Dexron types. Using a fluid that meets the Dexron VI specification helps ensure proper shifting, lubrication, and longevity. Dexron VI-H is available for certain high-temperature or heavy-load conditions, but many everyday driving scenarios do well with standard Dexron VI. Always verify with your owner’s manual or a GM service bulletin for the exact specification for your truck’s transmission code and usage (towing, climate, and mileage can influence the best choice).
Understanding GM’s transmission fluid requirement
GM transmission fluids are specified by Dexron VI and its variants. For most Sierra 1500 models around the 2018 vintage, Dexron VI is the standard requirement, and Dexron VI-H is an acceptable variant when higher heat or heavier duty conditions apply. Using older fluids such as Dexron III or Type F is not recommended for these transmissions, as it can affect shifting and longevity.
Recommended fluids for the 2018 GMC Sierra 1500
The following options meet GM’s Dexron VI specification and are commonly used in this model. Choose one based on availability, warranty guidance, and your typical driving conditions.
- Dexron VI (GM Dexron VI) from OEM-verified sources, such as GM/ACDelco Dexron VI. This is the standard, widely approved option for most driving scenarios.
- Dexron VI-H — An enhanced version of Dexron VI for higher temperatures or heavier duty service. Use this if your manual specifies Dexron VI-H or you regularly tow heavy loads in hot climates.
- Dexron VI Synthetic — A synthetic Dexron VI that can offer better high-temperature stability and extended drains, provided it carries the Dexron VI specification. Suitable for longer intervals or demanding conditions.
When selecting a fluid, ensure it explicitly meets the Dexron VI specification (and Dexron VI-H if your service requires it). Always prefer OEM-branded products or OEM-approved equivalents to avoid compatibility issues.
How to change or top up the transmission fluid
Fluids and procedures can vary by vehicle and transmission code. If you’re planning a DIY drain-and-fill, follow the factory guidelines and use the correct pan, filter, and gasket. If you tow frequently, drive in extreme heat, or are unsure about the service interval, consult a professional to perform a full fluid change or a professional flush when recommended by GM.
- Check the current fluid level with the dipstick when the engine is at operating temperature and the vehicle is level. Add slowly if needed until it reaches the correct mark. Do not overfill.
- Use the correct Dexron VI specification fluid only. Avoid fluids that do not state Dexron VI on the label.
- If you’re performing a drain-and-fill, consider replacing the filter if specified for your transmission code and mileage.
Regular maintenance with the proper Dexron VI fluid helps maintain smooth shifting, cold-weather performance, and transmission longevity. If you’re unsure about the exact specification for your Sierra 1500’s transmission code, consult the owner’s manual or a GM-certified technician.
Summary
For a 2018 GMC Sierra 1500, Dexron VI is the standard, recommended transmission fluid. Dexron VI-H is acceptable for certain service conditions, such as high heat or heavy towing. When in doubt, opt for an OEM-approved Dexron VI product (GM/ACDelco Dexron VI) or a reputable equivalent that explicitly meets the Dexron VI specification. Avoid older Dexron types, and always follow the owner’s manual or a GM service bulletin for the exact requirements. Regular, properly specified maintenance supports shifting performance and transmission life.