The Theta-II engine is known for oil leaks, often due to problems with the valve cover gasket or oil pan gasket.

Some owners report engine stalling issues, which could be due to a faulty crankshaft position sensor or issues with the fuel system.

The engine may experience timing chain tensioner problems, leading to a noisy engine and potential timing chain failure.

This engine is known for excessive oil consumption, often due to piston ring wear or other internal engine components.

Direct injection engines like the Theta-II GDI can suffer from carbon buildup on intake valves, leading to performance issues and rough idling.

Some engines develop knocking noises due to connecting rod bearing wear or issues with the fuel injection system.

Cooling system issues, such as a failing water pump or thermostat, can cause the engine to overheat.

Misfiring can occur due to faulty ignition coils, spark plugs, or fuel injectors.

Engine knocking in Hyundai Sonata vehicles, especially with the Theta-II engine, is a known issue. It is often caused by irregular combustion, which can be due to poor fuel quality, carbon buildup, or faulty components.

Excessive oil consumption has been reported in some 2017 Hyundai Sonata models. This can be due to worn piston rings or valve seals, leading to decreased engine performance and potential engine damage.

Some drivers have experienced unexpected engine stalling, which can be due to issues with the fuel delivery system, a faulty crankshaft position sensor, or problems with the engine control unit (ECU).

The Theta-II engine has been known to have issues with the timing chain tensioner, which can lead to improper timing chain operation, causing noise, reduced performance, and potential engine damage.

Fuel injector clogging or failure can result in poor engine performance, misfires, and reduced fuel economy. This is particularly a concern in direct injection engines like the GDI used in the Sonata.

Faulty knock sensors can lead to improper engine timing adjustments, resulting in knocking or pinging sounds and potential engine damage if not addressed.

Problems with the cooling system, such as a faulty thermostat or water pump, can lead to engine overheating, which can cause significant engine damage if not resolved promptly.

Premature wear of the connecting rod bearings, which can lead to engine knocking and eventually engine failure.

The engine may burn oil at a higher rate than normal, leading to low oil levels and potential engine damage if not monitored.

Problems with the timing chain tensioner or guides can cause timing chain slack, leading to poor engine performance or even catastrophic engine damage.

Direct injection engines like the GDI can suffer from carbon build-up on intake valves, leading to reduced performance and fuel efficiency.

Random stalling or rough idling, often attributed to issues with the fuel system or electronic control unit (ECU).

Problems with the radiator, water pump, or thermostat can cause overheating, which can severely damage the engine.

Worn piston rings can lead to compression loss, oil blow-by, and decreased engine efficiency.

Faulty ignition coils, spark plugs, or fuel injectors can cause engine misfires, leading to reduced performance and potential engine damage if not addressed.