GM Truck Owners With ‘Repaired’ 6.2L V8s File Lawsuit Over Decreased Fuel Efficiency

      2023 GMC Sierra AT4X AEV Edition. GMC

      Sign Up for The Drive’s daily newsletter

      Stay updated with the latest in automotive news, reviews, and features.

      General Motors seems to be having a difficult year. In addition to the ongoing V8 issue, the automaker is now facing a lawsuit regarding it. Given the extensive recall affecting over 600,000 trucks that require inspection and/or repairs, it’s not unexpected that a group of vehicle owners has come together to take legal action. What is surprising, however, is the reason for the lawsuit; these owners are not suing due to having their trucks out of service for extended periods or because of poor repair quality. Instead, they are taking action because GM’s fix for the problem is said to lead to reduced fuel efficiency.

      The issue stems from GM’s revised oil viscosity guidelines. Initially, the maintenance schedule for the L87 6.2-liter V8 called for 0W-20 motor oil. GM's new recommendation, however, has switched to 0W-40. A higher number in oil viscosity indicates that the oil is thicker. Oils with higher viscosity adhere better to engine components, thus improving lubrication but also creating more resistance.

      To illustrate, imagine swimming in a pool filled with vegetable oil instead of water. Setting aside buoyancy concerns, you would find it takes significantly more effort to move through the oil, regardless of how slippery it might feel. This scenario could reflect what’s happening to the L87’s internal parts, as trucks are powered by gasoline, not carbohydrates. Owners are apprehensive about needing significantly more fuel, leading to higher long-term expenses.

      “The use of thicker oil may or may not alleviate the engine issue, but it will certainly degrade fuel economy, forcing owners to purchase hundreds of additional gallons of gasoline throughout the life of their vehicles,” the lawsuit states. “Consequently, due to the inherent defect and GM’s recall solution, owners face two undesirable choices: take no action and risk severe engine damage, or proceed with the recall and incur extra costs for gasoline.”

      According to the 2025 Chevy Suburban owner’s manual found on Chevy’s website, the higher oil viscosity requirement does not apply to updated L87s installed in trucks produced after the recall period. The maintenance guidelines still list 0W-20.

      The lawsuit (McNamara et al. v. General Motors LLC) was initiated on behalf of seven owners in Pennsylvania, as reported by Law360.com (registration required), but they aim to include owners from across the country to strengthen their case.

      A representative from GM stated to The Drive that the company is reviewing the complaint but offered no additional comments.

      *While complex hydrocarbons can technically be considered carbohydrates with additional steps, please refrain from consuming hydrocarbons. Additionally, don’t attempt to swim in vegetable oil.

      Got tips? Send them to [email protected].