GM Duramax oil cooler lawsuit (Hubof v. General Motors)

An Idaho owner of a 2024 Chevrolet Silverado 2500 HD has sued General Motors LLC. He claims the engine oil cooler in GM's heavy-duty diesel pickups can crack or fail, sending engine oil into the cooling system and starving the engine of oil. The case is Hubof v. General Motors LLC, No. 2:26-cv-13622, filed September 24, 2026, in the U.S. District Court for the Eastern District of Michigan.

The proposed class covers people and businesses nationwide that bought or leased a 2024 to 2026 Chevrolet Silverado or GMC Sierra 2500HD or 3500HD with the 6.6-liter L5P Duramax diesel. No court has ruled, no class has been certified and there is no settlement. GM has issued dealer bulletins about oil in the coolant and oil cooler seal leaks, but we found no safety recall.

General Motors LLC makes, sells and warrants Chevrolet and GMC trucks, including the Silverado HD and Sierra HD.

The plaintiff, Robert Hubof, lives in Hayden, Idaho. According to the complaint, he bought his new truck from Knudtsen Chevrolet in Post Falls, Idaho, on December 5, 2023, for personal use.

He is represented by The Miller Law Firm (E. Powell Miller and Dennis A. Lienhardt), Sauder Schelkopf (Matthew D. Schelkopf and Joseph B. Kenney) and Walsh PLLC (Bonner C. Walsh). The case is assigned to Judge Robert J. White.

The complaint says that in June 2025, with about 16,453 miles on the truck, Hubof saw a low oil light and added about 7 quarts of oil. A few days later he heard a loud bang and found oil in the coolant degas bottle. A GM dealer told him the cooling system was filled with engine oil, the dipstick showed no oil and there was metal debris in the oiling system. He says the repair was not covered under warranty, he received a quote of $41,319.79 and the truck remains unrepaired and unusable.

GM had addressed related conditions in dealer documents before the suit. Service Update N232430450, dated August 2024 and marked "URGENT - DISTRIBUTE IMMEDIATELY," covers some 2024 heavy-duty trucks with the L5P engine. It says "engine coolant may have become contaminated" and tells dealers to inspect the coolant surge tank for an "oily black substance." It says a "small number of vehicles" are involved and does not name a cause.

Bulletin 25-NA-150, dated June 2025, covers 2024 and 2025 L5P trucks with an engine oil leak. It says the condition "may be caused by damaged engine oil cooler seals" and that "Engineering has found that many of the engine oil coolers returned, do not leak." It tells technicians to replace the seals first and the cooler only if needed, under Powertrain coverage. The complaint also cites a March 2025 GM bulletin, 25-NA-052, which it says linked oil in coolant to "a leaking engine cooler."

The complaint claims the oil cooler is "insufficiently strong and durable" for normal heat, pressure and vibration, so it can crack and let pressurized oil escape. It says this can cause overheating, loss of power, engine seizure and sudden engine failure. It claims GM knew of the problem from its own bulletins, warranty data and owner complaints but kept selling the trucks without disclosure, and that GM routinely denies coverage for resulting engine damage.

The complaint says GM's 3-year or 36,000-mile bumper-to-bumper warranty applies, and that GM's 5-year or 100,000-mile diesel powertrain coverage expressly lists the "integral oil cooler." It brings nine claims: the federal Magnuson-Moss Warranty Act, Michigan implied warranty, fraudulent concealment and unjust enrichment for the nationwide class, plus Idaho consumer protection, fraudulent concealment, express warranty, implied warranty and unjust enrichment claims.

GM has not filed a position on the claims. Its bulletins describe repair steps and, in 25-NA-150, point to seals rather than the cooler itself. They do not concede a defect. Class Action Pulse found no public GM statement about the lawsuit as of October 22, 2026.

According to the public docket, GM was served on September 29, 2026, with an answer due October 20. On October 19, GM filed a stipulation, an agreement between the parties, to extend its time to respond. The new deadline was not visible to us.

The court has not decided whether the oil cooler is defective, whether GM knew of a defect, whether the warranty limits apply or whether any class should be certified.

The proposed nationwide class is "All persons or entities in the United States that purchased or leased a Class Vehicle, other than for purposes of resale." The class vehicles are:

• 2024 to 2026 Chevrolet Silverado 2500HD and 3500HD with the 6.6-liter L5P Duramax
• 2024 to 2026 GMC Sierra 2500HD and 3500HD with the same engine
• 2027 versions of those trucks, only if they use the same or a substantially similar oil cooler design

An Idaho class of buyers and lessees is proposed in the alternative. GM and its affiliates and officers, the judge and the judge's family and staff, governmental entities and people with personal injuries from the alleged defect are excluded. The definition does not require that your truck has failed.

• Watch for oil in the coolant bottle, coolant loss, a low oil warning or overheating. If you see them, stop driving and have a GM dealer inspect the truck, since running without oil can destroy an engine.
• Ask the dealer whether your repair falls under GM's powertrain coverage or bulletin 25-NA-150. Get any denial in writing.
• Keep repair orders, estimates, towing and rental receipts, and photos of oil in the coolant.

No money is available from the lawsuit. The complaint asks the court to declare the cooling system defective, order GM-paid notice to owners, declare GM's warranty time and mileage limits unenforceable and require GM to re-audit denied warranty claims. It also asks for a repair program with inspections on request and coverage disputes decided by a court-appointed Special Master, damages, restitution or disgorgement, fees and interest. These are requests, not awards.

GM's existing warranties are a separate benefit. According to the complaint, the diesel powertrain coverage runs 5 years or 100,000 miles, whichever comes first.

• December 5, 2023: Hubof buys his truck.
• August 2024: GM issues Service Update N232430450.
• March 4, 2025: GM issues bulletin 25-NA-052, according to the complaint.
• June 2025: Hubof's engine fails; GM issues bulletin 25-NA-150.
• September 24, 2026: The complaint is filed.
• September 29, 2026: GM is served.
• October 19, 2026: The parties file a stipulation to extend GM's deadline.

The lawsuit has no claim, opt-out or objection deadlines.

• Engine oil cooler: A part that uses engine coolant to carry heat away from engine oil while keeping the two fluids apart.
• L5P: The engine code for GM's 6.6-liter Duramax turbo-diesel V8 in these trucks.
• Service bulletin: GM repair guidance for dealers. It is not a safety recall.
• Magnuson-Moss Warranty Act: A federal law that lets consumers sue over broken written or implied warranties.
• Special Master: A person the court appoints to handle a specific task, such as deciding coverage disputes.

GM is expected to answer the complaint or move to dismiss once the extended deadline arrives.

For our earlier report on the filing, see GM Duramax oil cooler lawsuit.

This article relies on the complaint, GM Service Update N232430450, GM bulletin 25-NA-150, the court docket and NHTSA recall data.

The defect, GM's knowledge and its warranty practices are allegations. We did not obtain bulletin 25-NA-052, so its wording comes from the complaint. The 2027 model year is included only conditionally. Our recall check covered Silverado 2500 and 3500 entries for 2024 to 2026 in NHTSA's data. The docket view comes from a public archive and may not show every filing. The number of affected trucks and GM's position are unknown.

Class Action Pulse is not a law firm or settlement administrator and does not guarantee eligibility or payment. This article is general information, not legal advice.