GM Duramax oil cooler lawsuit: 2024 to 2026 Silverado and Sierra HD engine failures

Estimated reading time: 10 minutes.

Key facts

What happened: An Idaho truck owner filed a proposed nationwide class action against General Motors on September 24, 2026. He claims the engine oil cooler in GM's 6.6-liter Duramax diesel heavy-duty pickups can crack, flood the cooling system with oil and destroy the engine.
Trucks named: 2024 to 2026 Chevrolet Silverado 2500HD and 3500HD and GMC Sierra 2500HD and 3500HD with the 6.6-liter L5P Duramax diesel, plus 2027 models if they use the same or a substantially similar oil cooler.
The owner's loss: The complaint says the plaintiff's 2024 Silverado 2500HD failed at about 16,453 miles, the repair was not covered under warranty, and he was quoted $41,319.79.
What GM has told dealers: GM service documents filed with federal regulators show an August 2024 service update for oil-contaminated coolant in some 2024 trucks, and a June 2025 bulletin saying "many of the engine oil coolers returned, do not leak."
No recall: We found no NHTSA safety recall for the oil cooler or cooling system on these trucks as of October 21, 2026.
Nothing to claim: There is no settlement or claim form. GM has not yet responded to the complaint in court.
The case: Hubof v. General Motors LLC, No. 2:26-cv-13622, U.S. District Court for the Eastern District of Michigan.

What the lawsuit claims

The 107-page complaint says the engine oil cooler in GM's current heavy-duty diesel pickups is not strong enough to handle normal driving. It claims the cooler can crack under the pressure, heat, vibration and repeated heating and cooling of everyday use.

When that happens, the complaint says, pressurized engine oil escapes into the engine's coolant or leaks out of the truck. It claims this can quickly drain the engine's oil and lead to overheating, loss of power, engine seizure and "sudden and catastrophic engine failure." The complaint calls this a safety risk because an engine can seize while the truck is moving.

The complaint makes four further claims:

Failures can happen early. It says the problem can appear at low mileage, within GM's new vehicle warranty.
Parts are scarce. It says replacement oil cooler system parts are on "national backorder," leaving owners without their trucks for months.
Warranty denials. It says GM points to low oil levels and metal debris to deny full engine replacement as a maintenance problem, sometimes paying only for a new cooler and a flush.
Same part, same risk. It says GM installs replacement coolers of the same design, so a repaired truck can fail again.

The complaint also says GM knew about the problem before selling these trucks, based on testing, warranty data, parts orders, owner complaints and its own service bulletins. GM has not filed a response, and these claims have not been proven.

How an oil cooler can fail

The 6.6-liter L5P Duramax is the diesel V8 offered in GM's 2500HD and 3500HD pickups. Like most diesels, it uses an oil cooler, a small heat exchanger that uses engine coolant to keep the engine oil from running too hot.

Inside the cooler, oil and coolant flow through separate passages divided by thin metal walls. Heat passes through the metal, but the two fluids are never supposed to mix. The complaint says that if the cooler cracks, the barrier fails. Because the oil is under higher pressure, it can be pushed into the cooling system.

According to the complaint and owner reports it quotes, warning signs can include a low oil warning, oil in the coolant overflow bottle (GM calls it the radiator surge tank), oil leaking under the truck, and an oily black film on top of the coolant.

Check your coolant bottle if you drive one of these trucks GM's own dealer instructions describe contamination as a film of oily black substance on top of the coolant in the surge tank. If you see that, or get a low oil warning, stop driving and have the truck inspected. Running an engine low on oil can cause severe damage.

The owner behind the case

The plaintiff is Robert Hubof of Hayden, Idaho. Court records spell his name Hubof, though parts of the complaint spell it Huboff.

According to the complaint, he bought a new 2024 Chevrolet Silverado 2500HD from Knudtsen Chevrolet in Post Falls, Idaho, on December 5, 2023, for personal use. He says the warranty was an important reason he bought the truck.

In June 2025, at about 16,453 miles, a low oil light came on. The complaint says he added about seven quarts of oil. A few days later he heard a loud bang, then found oil in the coolant bottle and oil leaking from under the truck.

At the dealer, a GM technician told him the cooling system was contaminated and filled with engine oil, the dipstick showed no oil, and there was metal debris in the oil system, according to the complaint. The complaint says the truck was not repaired under warranty and he was quoted $41,319.79 for repairs. It says the truck remains unrepaired and unusable.

The complaint also quotes five owner complaints filed with the National Highway Traffic Safety Administration (NHTSA). One owner of a 2024 Silverado 3500 wrote that at about 35,126 miles "the oil cooler cracked and flooded my engine cooling system with over 2.5 gallons of oil causing catastrophic engine failure." NHTSA does not verify owner complaints.

What GM has told dealers

GM sends repair instructions to dealers through service updates and technical service bulletins. These are not recalls. A recall is a formal safety campaign reported to NHTSA, with owner notification by mail. Service bulletins are repair instructions for technicians. Automakers file them with NHTSA, which posts them publicly.

Service Update N232430450 (August 14, 2024). This document, marked "URGENT - DISTRIBUTE IMMEDIATELY," covers certain 2024 Silverado and Sierra 2500HD and 3500HD trucks with the L5P engine. It says "the engine coolant may have become contaminated." Dealers were told to inspect the surge tank and, if contamination was visible, flush the system and replace the surge tank and a set of hoses, with 11.0 hours of warranty labor allowed. Affected trucks still in dealer hands had to be held and repaired before delivery.

The update does not name the oil cooler or any other cause. It describes "the small number of vehicles involved" and says it expires at the end of each truck's new vehicle limited warranty.

Service Bulletin 25-NA-052 (March 2025). According to the complaint, this broader bulletin, which covers many GM vehicles, tells technicians: "If you found oil in the coolant and the engine is otherwise healthy, this may be caused by a leaking engine oil cooler." It directs replacing the cooler and flushing the system.

Service Bulletin 25-NA-150 (June 2025). This bulletin, which the complaint does not mention, covers 2024 and 2025 Silverado and Sierra 2500HD and 3500HD trucks with the L5P. It addresses customer reports of an oil leak and says "this condition may be caused by damaged engine oil cooler seals." It adds: "Engineering has found that many of the engine oil coolers returned, do not leak." Technicians are told to remove the cooler and inspect the seals, replace the seals if they are damaged, and replace the cooler only if the seals look fine. The repair is listed under GM's powertrain coverage.

The complaint argues that these documents show GM knew about the problem. The June 2025 bulletin points to seals rather than cracked coolers as a likely cause of some leaks. A court has not decided what the documents prove.

Warranty coverage and denials

According to the complaint, GM's warranty for these trucks includes 3 years or 36,000 miles of bumper-to-bumper coverage and 5 years or 100,000 miles of powertrain coverage for the Duramax diesel. The complaint says GM's warranty booklet lists the "integral oil cooler" as a covered diesel component.

The dispute is over what happens after the cooler fails. The complaint says GM has blamed low oil and the resulting engine damage on poor maintenance, and denied coverage for full engine replacement. It argues that a cracked cooler is what drains the oil in the first place, so the low oil reading is a symptom of the defect, not the owner's fault.

GM has not publicly responded to that argument, and we found no GM statement on the lawsuit.

Ask for your repair records in writing If a dealer finds oil in your coolant, ask for a written repair order that states what was found, what caused it and why any part of the repair was denied. Keep your oil change receipts, since maintenance history is often central to these warranty disputes.

Who is suing and what they want

Hubof 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 defendant is General Motors LLC, based in Detroit.

The complaint proposes a nationwide class of "all persons or entities in the United States that purchased or leased a Class Vehicle, other than for purposes of resale," with an Idaho class as an alternative. It seeks damages for owners who paid out of pocket for repairs, and declaratory relief for owners whose trucks have not yet failed.

It brings nine claims, including violation of the federal Magnuson-Moss Warranty Act, breach of implied warranty under Michigan law, fraudulent concealment, unjust enrichment, and claims under Idaho's Consumer Protection Act and warranty law.

The complaint asks the court to:

Certify the class and appoint Hubof and his lawyers to represent it
Declare the oil cooler system defective and require GM to notify owners
Declare that the warranty's time and mileage limits cannot be enforced for this defect
Require GM to re-review all prior denied warranty claims tied to the defect
Set up an inspection and repair program, with disputes decided by a court-appointed special master
Award damages, including punitive damages, plus restitution, attorneys' fees and interest

Where the case stands

The case is before U.S. District Judge Robert J. White in Detroit. GM was served on September 29, 2026, making its response 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 in the public records we checked.

The case has not been certified as a class action. GM's next step is usually an answer or a motion to dismiss.

What owners can do now

If your truck shows signs of oil in the coolant. Stop driving and contact a GM dealer. Ask whether any service update or bulletin applies to your VIN.

If GM denied coverage for an engine repair. Keep the denial, repair orders and maintenance records. You can ask GM customer care to review the decision. The lawsuit does not change any current warranty decision.

If you want to follow the case. You do not need to do anything to stay in the proposed class. If a class is certified or a settlement is reached, class members would normally receive notice.

If you want a case you can act on now. See our list of class action cases you can join.

No Duramax settlement exists Ignore messages that promise a GM oil cooler settlement payment in exchange for your VIN, bank details or a fee. This case has no settlement or claim process.

What remains unclear

GM's position. GM has not filed a response, and we found no public statement.
How often coolers fail. The complaint does not give a failure rate, and GM's 2024 update described a small number of trucks. GM's 2025 bulletin says many returned coolers did not leak.
Whether 2027 trucks are affected. The complaint includes 2027 models only if they use the same or a substantially similar cooler, which it says discovery would determine.
NHTSA action. We found no recall or open investigation for this condition as of October 21, 2026.
The response deadline. GM's extended deadline was not shown in the records we reviewed.

This article is for information only and is not legal advice. Owners with questions about their own truck should contact a GM dealer or a licensed attorney.

Frequently asked questions

Which trucks are in the GM Duramax oil cooler lawsuit?

The complaint names 2024 to 2026 Chevrolet Silverado 2500HD and 3500HD and GMC Sierra 2500HD and 3500HD trucks with the 6.6-liter L5P Duramax diesel. It also seeks to include 2027 models with the same or a substantially similar oil cooler.

Is there a recall for the Duramax oil cooler?

We found no NHTSA safety recall for the oil cooler or cooling system on these trucks as of October 21, 2026. GM has issued a service update and bulletins to dealers, which are not recalls.

Can I join the Duramax oil cooler class action?

The proposed class includes anyone in the United States who bought or leased one of these trucks other than for resale. No class has been certified, and there is no claim form. Class members would receive notice if a class is certified or a settlement is reached.

What are the signs of a failed oil cooler?

According to the complaint and GM's dealer instructions, signs include a low oil warning, oil in the coolant bottle, an oily black film on the coolant and oil leaking under the truck. Have the truck inspected promptly if you notice these.

Does GM's warranty cover the oil cooler?

The complaint says GM's 5-year or 100,000-mile powertrain warranty for the Duramax lists the integral oil cooler as covered. The dispute is over whether GM must also pay for engine damage when a cooler fails.

What did GM say in its June 2025 bulletin?

Bulletin 25-NA-150 says oil leaks on 2024 and 2025 L5P trucks may be caused by damaged oil cooler seals, and that "many of the engine oil coolers returned, do not leak." It tells technicians to check and replace the seals before replacing the cooler.