A Hyundai engine lawsuit claims 2015-2016 Sonata, Tucson and Santa Fe vehicles with Theta 2-liter and 2.4-liter gasoline direct injection (GDI) engines have defects that cause thousands of dollars to repair.

The proposed class-action lawsuit was filed by two Hyundai owners who claim the engines are damaged due to restricted oil flow, typically causing damage to the Theta engines that can't be repaired unless the engines are replaced.

The plaintiffs say they paid thousands of dollars to replace engines they thought were free from defects based on Hyundai's advertising.

According to the lawsuit, Hyundai has actively concealed the Theta engines are prone to damage and failure caused by the connecting rod bearings, leaving owners in the dark until they experience engine problems.

The plaintiffs say if Hyundai would have admitted the engines were defective, owners wouldn't have paid as much for the cars, or possibly not purchased the vehicles in the first place.

The plaintiffs claim Hyundai has known about the Theta engine problems for years, especially through customer complaints and warranty claims, yet dealers have the habit of denying the existence of a defect. Many times, Hyundai allegedly refuses to repair or replace the engines even when the vehicles are still under warranty.

Hyundai has recalled vehicles in the past due to problems with metallic debris from the crankshafts that restricts oil flow to the connecting rod bearings. Without enough oil flow to cool the engine components, the temperature of the bearings causes excessive wear and tear and a knocking noise from the engines.

Owners also report illuminated oil pressure lights and even engines catching on fire. According to previous lawsuits filed about the Theta engines, the problem is brought about by the way Hyundai removed machining debris from the crankshafts.

Affected owners who say they experienced the problems complain about the dangers of stalling in traffic and the hassle of being stranded without a working car.

The Hyundai engine lawsuit was filed in the U.S. District Court for the Central District of California - Coats, et al., v. Hyundai Motor Company, et al.

The plaintiffs are represented by McCune Wright Arevalo LLP, the Sultzer Law Group P.C., and Walsh PLLC.

Hyundai and Kia have faced legal battles over the Theta engines before, including one filed concerning Sonata cars. That lawsuit came out in favor of the plaintiffs who allege 2011-2012 Sonatas have engine defects. Hyundai had recalled the cars in 2015, then federal safety regulators opened an investigation to determine if the recall was enough to fix the cars.

In addition, Hyundai accused one of its engineers of talking to the U.S. government. Japanese media reported at the time that Hyundai petitioned a court by accusing the longtime Hyundai engineer with passing corporate secrets to federal safety regulators.