Hyundai Smartstream 2.5L Engine: Known Reliability Concerns

The 2.5-liter Smartstream four-cylinder is a widely used engine across Hyundai, Kia, and Genesis vehicles, including the Sonata, Santa Fe, Tucson, Sportage, Sorento, K5, and GV80. It comes in naturally aspirated, turbocharged, and hybrid forms, producing between 187 and 300 horsepower depending on the model.

4-liter Theta II, long-term reliability data is still emerging. Early reports suggest it is more reliable than the Theta II, which had known connecting rod bearing failures. Some owners say their Smartstream-powered cars have passed 150,000 miles with regular servicing.

Still, some early production versions from 2021 to early 2023 are known for excessive oil consumption, with some using up to one quart per 1,000 miles. The issue involves piston rings that can allow oil into the combustion chamber. Over time, carbon deposits may build up, causing misfires, knocking, power loss, and higher fuel use.

A mid-2023 redesign reportedly improved this on newer models.

Direct injection also makes carbon buildup on intake valves likely near 100,000 miles. Certain engines built between late 2019 and late 2020, including some 2020-2021 Sonata models, have had clogged EGR valves leading to rough idling and poor performance.

Some naturally aspirated engines have also had faulty fuel injectors that leak fuel into the cylinder, causing stalling, hesitation, or sudden power loss. Affected models include certain Sonata, Santa Fe, Sorento, Tucson, and Sportage vehicles from the 2020-2024 model years.

Recalls have also been issued. Some 2025-2026 Santa Fe, Tucson, Sorento, and K4 models built between February 18 and August 8, 2025 were recalled for connecting rod bolts that were not tightened enough, which could lead to stalling, knocking, or engine seizure. Some 2024-2025 Santa Fe turbo models were recalled for an improperly installed starter motor positive terminal cover posing a fire risk.

There have also been reports of faulty Integrated Thermal Management Modules failing after as little as 30,000 miles, causing severe overheating and possible cylinder head damage.