GM Oil Cooler Lawsuit, Silverado HD and Sierra HD Owners Accuse GM of Hiding Duramax Defect

General Motors LLC faces a putative class action alleging that engine oil coolers in certain heavy-duty Chevrolet Silverado and GMC Sierra diesel trucks can crack, letting oil leak out or mix with coolant and potentially causing severe engine damage. The case, Hubof v. General Motors LLC, No. 2:26-cv-13622, was filed September 24, 2026, in the U.S. District Court for the Eastern District of Michigan. It focuses on trucks with the 6.6-liter L5P Duramax diesel engine. [1][2]

Plaintiff Robert Hubof says his 2024 Silverado 2500HD failed at about 16,453 miles and that he received a repair estimate of $41,319.79. He alleges GM knew about the problem, did not adequately warn buyers and wrongly refused full warranty coverage. These are allegations, not findings. GM’s service documents (below) are relevant, but they do not by themselves prove a fleet-wide defect or concealment.

There is no settlement, no certified class and no claim form. The $41,319.79 figure is one owner’s alleged estimate, not a payout for anyone else.

GM Duramax Oil Cooler Lawsuit: Quick Facts

Detail	Information
Case name	Hubof v. General Motors LLC
Case number	2:26-cv-13622
Court	U.S. District Court, Eastern District of Michigan
Filed	September 24, 2026
Plaintiff	Robert Hubof
Defendant	General Motors LLC
Alleged defect	Engine oil cooler cracks or fails, letting oil leak or enter the cooling system
Vehicles at issue	Certain 2024–2026 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD trucks with the 6.6L L5P Duramax diesel; certain 2027 models only if they use the same or a substantially similar assembly
Plaintiff’s alleged repair estimate	$41,319.79
Proposed classes	Nationwide purchasers and lessees; an Idaho class is also proposed
Class certified?	No
Settlement?	None announced
Claim form or deadline?	None announced
Recall?	No NHTSA recall for the alleged oil-cooler defect identified as of October 21, 2026

The docket lists the case as a motor-vehicle product-liability matter. [1]

Which Chevrolet Silverado HD and GMC Sierra HD Trucks Does the GM Lawsuit Cover?

The proposed vehicle group is:

• 2024, 2025 and 2026 Chevrolet Silverado 2500HD and 3500HD with the covered engine.
• 2024, 2025 and 2026 GMC Sierra 2500HD and 3500HD with the covered engine.
• Possibly certain 2027 models, if they use the same or a substantially similar oil-cooler assembly.

The final definition depends on the complaint and later rulings. Gas trucks, light-duty models and other Duramax variants should not be assumed to be included. Even within the listed model years, having an L5P engine does not mean your truck has the alleged defect.

How Does a Duramax L5P Engine Oil Cooler Work, and What Is Alleged to Go Wrong?

An oil cooler is a heat exchanger. Coolant flows through it to carry heat away from engine oil while keeping the two fluids apart. If the cooler cracks or its seals fail, oil can leak outside or enter the cooling system.

The complaint alleges the cooler cannot reliably withstand the pressure, temperature swings and vibration of normal use. It claims a failure can lead to oil in the coolant, external oil leaks, loss of lubrication, overheating, engine seizure and repair bills in the tens of thousands of dollars. [2]

These are the alleged consequences, not a finding that every cooler fails or that every leak causes all of them. Oil in coolant can also have other causes, so a technician must identify the actual source.

What Happened to Robert Hubof’s 2024 Chevrolet Silverado 2500HD?

According to the complaint as summarized in reporting:

• December 2023: Hubof bought a new 2024 Silverado 2500HD for personal use, relying on GM’s warranties and reliability claims.
• June 2025: At about 16,453 miles, a low-oil warning appeared and he added about seven quarts of oil. Days later he heard a loud bang and found oil in the coolant reservoir and leaking under the truck.
• Dealer findings: A dealership technician allegedly found engine oil in the cooling system and metal debris in the oil system, and the dipstick showed no oil.
• The estimate: Hubof says GM did not cover the full repair under warranty and that he received an estimate of $41,319.79. The truck allegedly remained unrepaired and unusable when he sued. [2][6]

The $41,319.79 figure is the plaintiff’s alleged estimate. It is not a typical oil-cooler repair price, a court award or a settlement amount. Costs depend on the cause, the engine’s condition, the parts needed and the warranty.

What Do GM’s Service Documents Say About Oil Cooler and Coolant Problems?

The complaint relies on GM’s own documents to argue GM knew about the problem. Reading them carefully matters, because they cut both ways.

GM Service Update N232430450 (August 14, 2024): Possible Engine Coolant Contamination

This update covered certain 2024 Silverado 2500HD/3500HD and Sierra 2500HD/3500HD trucks with the 6.6L L5P. Dealers were told to inspect the radiator surge tank and, if contamination was visible, order parts and repair the vehicle, including a coolant flush and replacement of the surge tank and hoses. Involvement was to be checked through GM’s internal vehicle-history system. [3]

It shows GM addressed possible coolant contamination in a defined group of 2024 trucks. It does not say the oil cooler caused every case, and it does not say every L5P truck is affected. A service update is also not a safety recall.

GM Service Bulletin 25-NA-052 (March 2025): Flushing Oil Contamination From the Cooling System

This bulletin covers a wide range of GM vehicles from model years 2000 through 2025. It says that when oil is found in coolant and the engine is otherwise healthy, a leaking engine oil cooler may be the cause, and it gives flushing and parts-replacement instructions. [4]

It describes a recognized diagnostic possibility. Because it covers many vehicles, it does not by itself establish the defect alleged in this case.

GM Service Bulletin 25-NA-150 (June 2025): Engine Oil Leak, Oil-Cooler Seals

This bulletin covers specified 2024 and 2025 Silverado HD and Sierra HD trucks with the L5P. Technicians are told to inspect the oil-cooler seals before replacing the whole cooler. If the seals are visibly damaged or have debris that could cause a leak, replace the seals. If not, proceed with cooler replacement. A GM technical summary published in July 2025 similarly says some 2024–2026 leaks may come from damaged cooler seals rather than the cooler itself. [5]

This qualifies the plaintiff’s theory. A defective cooler and a damaged seal are different causes, and the procedure tells technicians to diagnose the leak rather than assume the cooler is at fault. The bulletin does not resolve whether GM concealed a systemic defect or whether Hubof’s claim was properly denied.

Does a GM Service Bulletin Prove GM Hid a Defect?

No. A bulletin can be evidence of what a manufacturer knew, but its existence does not establish fraud. The wording, scope and date of each document, internal company knowledge, customer disclosures and the facts of each repair all matter. GM can dispute the claims.

Why Do GM Technical Service Bulletins Appear in NHTSA’s Database?

Under 49 C.F.R. § 579.5, manufacturers must provide NHTSA with copies of communications sent to dealers about defects and service issues. That is why GM’s bulletins are publicly searchable in NHTSA’s technical-bulletin database. Reports to NHTSA are not admissions of a safety defect.

Why Does the GM Duramax Warranty Dispute Matter?

The lawsuit alleges not only that the cooler can fail but that GM wrongly refuses to pay for the resulting damage. According to the complaint, GM sometimes blames low oil or metal debris on poor maintenance and may pay for a cooler replacement and cooling-system flush while declining to cover the engine. The complaint also alleges replacement coolers may have the same weakness and that replacement parts have faced long backorders that leave trucks unusable. [2][6]

Hubof argues cause and effect run the other way: low oil may be a symptom of a leaking cooler, not proof of neglect. That depends on the facts of each failure. Low oil has several possible causes, and metal debris alone does not prove a cooler defect. None of this has been decided. GM’s full public response was not available in the reporting reviewed through October 22, 2026.

What GM Warranty Coverage Should Silverado and Sierra HD Owners Review?

Coverage depends on your truck’s warranty booklet, in-service date, mileage, maintenance history, diagnosis and exclusions. Ask the dealer to identify the warranty provision in writing and to explain any denial. If GM says maintenance caused the failure, ask for the diagnostic findings behind that conclusion.

What Federal and State Laws Does the Hubof v. General Motors Lawsuit Rely On?

The complaint reportedly pleads nine counts, including warranty claims, fraudulent concealment, unjust enrichment and consumer-protection claims, and invokes the federal Magnuson-Moss Warranty Act and Idaho law. Confirm the exact counts in the complaint. [2][6]

Magnuson-Moss Warranty Act (15 U.S.C. §§ 2301–2312)

This federal law governs written and implied warranties on consumer products, including vehicles. Section 2310(d) lets consumers sue for breach of warranty, and it allows a prevailing consumer to recover attorney fees. Federal courts generally hear these claims only if the amount in controversy meets the statute’s threshold, so class-wide Magnuson-Moss claims are often paired with other jurisdictional bases. A broken vehicle does not automatically mean a violation; the warranty’s terms and the cause of failure control.

Breach of Express and Implied Warranty (Uniform Commercial Code §§ 2-313, 2-314, 2-725)

Express warranties arise from the manufacturer’s promises. The implied warranty of merchantability says goods must be fit for ordinary purposes. Disputes often turn on notice, privity, disclaimers, warranty duration and the link between the defect and the loss. The UCC’s general limitation period is four years from delivery (§ 2-725), though states vary and fraudulent-concealment arguments can affect timing.

Fraudulent Concealment

The plaintiff alleges GM knew of the defect and did not disclose it. Depending on the law, the plaintiff must show knowledge, a duty to disclose, materiality, intent, reliance and damages. Fraud claims must be pleaded with particularity under Federal Rule of Civil Procedure 9(b). Bulletins and owner complaints can be evidence but do not prove every element.

Idaho Consumer Protection Act (Idaho Code § 48-601 et seq.)

The complaint reportedly invokes Idaho consumer-protection law, alleging GM failed to disclose material information and marketed the trucks without disclosing the alleged problem. The available remedies and the claim’s viability depend on how it is pleaded and how the court rules.

Unjust Enrichment

The plaintiff alleges GM kept money from selling affected trucks while failing to disclose the problem and provide relief. Courts decide whether this equitable claim can proceed alongside the warranty and statutory claims.

Why Is the Case in Federal Court?

Class actions with more than 100 class members, more than $5 million in controversy and minimal diversity can be heard in federal court under the Class Action Fairness Act (28 U.S.C. § 1332(d)). The complaint’s jurisdictional allegations should be checked against the docket.

Does the Safety Recall Law Apply?

The National Traffic and Motor Vehicle Safety Act (49 U.S.C. §§ 30118–30120) requires manufacturers to notify owners and remedy safety-related defects. A private lawsuit is a separate track from a recall. No recall for this alleged defect has been identified.

What Is the Proposed Class in Hubof v. General Motors LLC?

Hubof seeks to represent a nationwide class of people and businesses that bought or leased covered vehicles for purposes other than resale, plus an Idaho class. A putative class becomes a class only if the court certifies it under Federal Rule of Civil Procedure 23. The plaintiff must satisfy Rule 23(a) (numerosity, commonality, typicality and adequacy of representation) and, for a damages class, Rule 23(b)(3) (common issues predominate and a class action is the superior method).

The court may narrow the model years, limit state-law claims or require separate treatment of different issues. Owning a listed model does not make you a confirmed class member, and there is no class notice or claims program.

Does the Lawsuit Pause the Clock for Other Owners?

Under American Pipe & Construction Co. v. Utah, 414 U.S. 538 (1974), filing a class action generally pauses the statute of limitations for putative class members while class certification is pending. State-law application can vary, and individual claims have their own deadlines, so owners with a denied or expensive repair should not simply wait. Speak to a lawyer about your own deadlines.

What Relief Is Robert Hubof Asking the Court to Order?

The complaint reportedly seeks:

• Class certification to represent owners and lessees who meet the court-approved definition.
• Damages for eligible repair costs and other losses proven.
• Warranty-related relief, including a declaration on GM’s warranty obligations and the time or mileage limits the plaintiff challenges.
• Review of prior warranty denials linked to the alleged problem.
• A court-supervised inspection and repair program for eligible vehicles.
• Notice to owners about the alleged defect.
• Restitution, punitive damages where permitted, attorney fees, costs and interest.

These are requests, not orders. No compensation amount for other owners can be predicted.

Is There an NHTSA Recall for the GM Duramax Oil Cooler?

A lawsuit and a recall are separate processes. A lawsuit asks a court to resolve claims between parties. A safety recall involves a determination that a vehicle or part presents an unreasonable safety risk or fails a federal standard.

As of October 21, 2026, no NHTSA recall for the oil-cooler defect alleged here was identified. That does not mean your truck has no other recalls or service campaigns. Look up your VIN on NHTSA’s recall tool and ask a dealer to check for open service updates. [7]

What Should Chevrolet Silverado HD and GMC Sierra HD Owners Do Now?

1. Stop driving if there are serious warning signs. Low oil pressure, severe overheating, a major oil leak or oil in the coolant means stop safely and call a qualified shop. Do not assume topping off oil or coolant makes the truck safe.
2. Get a written diagnosis. Ask whether oil was found in the coolant, whether the cooler, seals or another part was the source, whether metal debris was found, and why a full repair was approved or denied.
3. Keep maintenance and warranty records. Save oil-change invoices, repair orders, photos, diagnostic reports, towing and rental receipts, and all communications with GM or the dealer. Ask for any warranty denial in writing.
4. Have a dealer check your VIN for open service updates and ask whether the coolant-contamination update or the oil-cooler diagnostic procedures apply.
5. Keep proof of out-of-pocket costs, including invoices, proof of payment, dates, mileage and the shop’s diagnosis.
6. Report problems to NHTSA at NHTSA.gov. A complaint does not by itself lead to a recall.
7. Review your own legal options. State lemon laws, warranty rights and consumer-protection statutes differ and depend on your facts. If a major repair was denied or the truck is unusable, consider an auto-warranty or consumer-law attorney.

Be careful with anyone offering to register you for a payout. No claim process exists for this lawsuit.

How Do Other General Motors Lawsuits Differ From the Duramax Oil Cooler Case?

• GM Transmission Lawsuit, Were You Affected? — Barba v. General Motors, No. 4:26-cv-13030 concerns alleged transmission problems, not oil coolers.
• GM CVT Transmission Lawsuit, Were You Affected? — Williams v. General Motors LLC, No. 1:26-cv-01162 involves continuously variable transmissions in certain Chevrolet and GMC vehicles, with a different vehicle scope and legal theory.
• Duramax Owners, CP4 Pump Destroyed Your Engine? Claim Deadline PASSED—But You Still Have Options Until May 2026 covers earlier Duramax trucks and alleged fuel-pump failures. The CP4 litigation does not decide the oil-cooler case.

What Are the Tax and Attorney-Fee Rules if the GM Oil Cooler Case Settles?

Nothing has settled, so this is general information only.

• Fees: In a class settlement, the judge must approve class counsel’s fees (Federal Rule of Civil Procedure 23(h)). Fees may come from a common fund or be paid separately by the defendant, and Magnuson-Moss and some state statutes allow fee-shifting.
• Objections: If a settlement is proposed, class members can object under Rule 23(e)(5), and the court holds a fairness hearing before final approval.
• Taxes: Reimbursement of out-of-pocket repair costs is generally treated differently from other income, but tax treatment depends on your situation. Consult a tax professional.

What Happens Next in Hubof v. General Motors LLC?

Likely next steps are GM’s response, motions challenging some or all claims (such as a motion to dismiss under Federal Rule of Civil Procedure 12(b)(6)), exchange of evidence and, later, a class-certification decision. Discovery in cases like this commonly covers GM’s engineering records, warranty-claim data, supplier quality records and communications about the bulletins.

The public Justia docket copy reviewed the September 24 filing, summons and related entries and warned that newer entries might be on PACER. Separate reporting published October 21 said GM filed a stipulation on October 19 seeking more time to respond. The new deadline was not confirmed. [1][6] Check the live PACER docket before describing the case as pending, settled or dismissed.

If a class is certified, the court’s definition and notice process will determine who is included. If the case settles, the agreement must set out eligibility, relief and any claim procedure. None exists yet.

GM Duramax Oil Cooler Lawsuit Timeline

Date	Event
December 2023	Hubof says he bought a new 2024 Silverado 2500HD
August 14, 2024	GM issues Service Update N232430450 on possible coolant contamination
March 2025	GM publishes Bulletin 25-NA-052 on flushing oil contamination
June 2025	GM publishes Bulletin 25-NA-150 on oil-cooler seals; Hubof alleges his truck failed at about 16,453 miles
September 24, 2026	Hubof v. General Motors LLC filed in the Eastern District of Michigan
October 19, 2026	Reporting says GM filed a stipulation seeking more time to respond
October 22, 2026	No certified class, settlement or claim form identified

Frequently Asked Questions About the GM Duramax Oil Cooler Lawsuit

Is there a GM Duramax oil cooler class action?

There is a putative class action, Hubof v. General Motors LLC, No. 2:26-cv-13622, filed September 24, 2026, in the Eastern District of Michigan. No class has been certified.

Which trucks are included?

Certain 2024–2026 Chevrolet Silverado 2500HD/3500HD and GMC Sierra 2500HD/3500HD trucks with the 6.6L L5P Duramax diesel. Certain 2027 models may be included if they use the same or a substantially similar assembly.

How much could owners receive?

No payout amount has been set. The $41,319.79 figure is Hubof’s alleged repair estimate.

Is the GM oil cooler lawsuit settled?

No settlement was identified as of October 22, 2026.

Is there a claim form or deadline?

No. Do not pay anyone offering to register you.

Has a judge certified the class?

No. The nationwide and Idaho classes are proposals only.

Is there an official recall for the oil-cooler problem?

None was identified for the defect alleged here as of October 21, 2026. Check your VIN on NHTSA’s tool.

Does the August 2024 service update prove the cooler is defective?

No. It shows GM addressed possible coolant contamination in certain 2024 trucks. It does not establish the cause across the fleet or prove concealment.

Can damaged oil-cooler seals cause the leak instead of the cooler?

Yes. Bulletin 25-NA-150 tells technicians to inspect the seals first and replace them if damaged, and to replace the cooler if the seals do not show the specified problem.

What should I do if GM denied my engine repair under warranty?

Keep the denial, estimate, diagnostic report, maintenance history, VIN and proof of payment, ask for the factual basis in writing, and consider an auto-warranty or consumer-law attorney.

Is this the same as the GM CP4 fuel-pump settlement?

No. The CP4 case concerned a different component and different model years.

Has GM admitted the oil cooler is defective?

No admission was identified. The court will decide on the evidence.

Sources and Documents

1. U.S. District Court, Eastern District of Michigan, Hubof v. General Motors LLC, No. 2:26-cv-13622, public docket. The public copy reviewed was last retrieved September 24, 2026; later filings may be on PACER.
2. ClassAction.org, Class Action Lawsuit Claims 2024–2027 Chevy Silverado, GMC Sierra Diesel Models Plagued by Engine Oil Cooling System Defect, October 20, 2026.
3. General Motors, Service Update N232430450, Possible Engine Coolant Contamination, August 14, 2024 (NHTSA technical-bulletin database).
4. General Motors, Service Bulletin 25-NA-052, Information on Flushing Oil Contamination from Cooling System, March 2025 (NHTSA technical-bulletin database).
5. General Motors, Service Bulletin 25-NA-150, Engine Oil Leak, June 2025.
6. Class Action Pulse, GM Duramax oil cooler lawsuit: 2024 to 2026 Silverado and Sierra HD engine failures, October 21, 2026.
7. National Highway Traffic Safety Administration, Recall lookup and vehicle-safety information.

Statutes, rules and cases cited: 15 U.S.C. §§ 2301–2312; 28 U.S.C. § 1332(d); 49 U.S.C. §§ 30118–30120; 49 C.F.R. § 579.5; Fed. R. Civ. P. 9(b), 12(b)(6), 23; Idaho Code § 48-601 et seq.; UCC §§ 2-313, 2-314, 2-725; American Pipe & Construction Co. v. Utah, 414 U.S. 538 (1974).

Disclaimer: This article is general information, not legal advice. The allegations come from a complaint and have not been proven in court. Rely on a qualified technician for diagnosis and consult your warranty documents or an attorney about your own claim.

Researched and written by Israr Ahmad, legal content researcher and founder of AllAboutLawyer.com. All facts verified against the federal docket listing for No. 2:26-cv-13622, GM’s service documents in NHTSA’s technical-bulletin database, ClassAction.org and Class Action Pulse reporting, and the cited statutes, rules and Supreme Court decision, as of October 22, 2026. Last Updated: October 22, 2026.