The engine uses Dexos1 Gen 2 motor oil, most commonly in 5W-30; always confirm the exact grade and capacity in your owner's manual or on the under-hood label.
The 6.6L gasoline V8 is used in GMC heavy‑duty trucks such as the Sierra 2500HD and 3500HD. Because oil specifications are tied to Dexos certification and model-year changes, the precise grade can vary by year and climate. This article outlines the typical requirements and how to verify them for your exact vehicle.
Oil grade and viscosity options
Before listing the common options, note that GM typically specifies Dexos1 Gen 2 5W-30 for most climates, with 0W-20 reserved for certain engines or conditions. The exact grade can differ by year and market.
- Dexos1 Gen 2 approved oil, 5W-30, for the majority of 6.6L gas engines
- Dexos1 Gen 2 approved oil, 0W-20, in specific model years or climates as indicated by GM
- Preferred to use synthetic or synthetic-blend oils that meet the Dexos1 Gen 2 specification
Always verify the exact grade on the oil fill cap or in the owner's manual to ensure compatibility with your vehicle’s configuration.
Oil capacity and service intervals
Before listing capacities and intervals, keep in mind that the typical oil fill for the 6.6L gas engine is around 8 quarts (about 7.6 liters) with filter, though exact capacity can vary by model year and engine configuration.
- Oil capacity: approximately 8 quarts (7.6 L) with filter
- Change interval: roughly every 7,500–10,000 miles (12,000–16,000 km) under synthetic Dexos1 Gen 2, or as indicated by the vehicle’s oil life monitoring system
Always follow GM’s recommended service intervals and rely on the vehicle’s oil life monitor for the most accurate timing.
How to verify the exact specification for your vehicle
Steps to confirm the right oil for your exact truck
- Consult the owner's manual for the recommended viscosity and Dexos specification for your year and trim.
- Inspect the under-hood oil fill cap or a nearby label for the Dexos1 Gen 2 specification and the suggested viscosity (for example, 5W-30).
- If in doubt, contact a GM dealer or use your VIN to pull the exact oil specification tailored to your vehicle.
Using the correct Dexos specification and viscosity helps protect the engine and maintains warranty coverage.
About Dexos certification and oil brands
Oils used in Dexos1 Gen 2‑compliant GM engines must meet the Dexos1 Gen 2 standard. Many reputable brands offer Dexos1 Gen 2 oils in 5W-30 (and some in 0W-20) viscosities. Look for Dexos1 Gen 2 labeling on the bottle and ensure the viscosity matches GM’s specification for your engine.
Brand familiarity matters less than meeting the Dexos1 Gen 2 spec and the correct viscosity for your climate and engine configuration.
Summary
For GMC’s 6.6L gas V8 in heavy‑duty trucks, use Dexos1 Gen 2 motor oil, typically 5W-30, with an approximate capacity of 8 quarts (7.6 L) including the filter. Some model years or climates may call for 0W-20. Always check your owner’s manual or the under-hood label and follow the vehicle’s oil life monitor to determine the precise change intervals. When in doubt, consult a GM dealer for VIN‑specific guidance.