About This Engine

The 2015 Kia Optima used two engine choices: the 2.4L Theta II GDI (G4KJ) inline four producing 200 hp and 186 lb-ft, and the 2.0L Theta II Turbo GDI (G4KH) producing 274 hp and 269 lb-ft. Both are part of Hyundai-Kia's Theta II family, both use cast aluminum blocks with iron liners, both run direct injection, and both feature Dual CVVT for variable timing on intake and exhaust cams. The 2.4L was the volume engine, fitted to the LX and EX trims, while the 2.0L Turbo was the performance engine, fitted to the SX, SXL, and Limited trims.

Important Theta II Buyer Information

Theta II engines, including the G4KJ and G4KH, were the subject of a multi-year recall and warranty extension by Hyundai and Kia after a connecting rod bearing wear issue caused premature engine failures on a portion of production. Hyundai-Kia eventually extended the powertrain warranty on covered Theta II engines to 10 years or 120,000 miles. We inspect every Theta II engine we ship for the bearing wear signature (knock, low oil pressure, metallic debris in the oil pan) and disclose findings before shipping. For 2015 Optima owners replacing a failed Theta II under or just past the extended warranty window, a tested used unit is the most cost-effective path back on the road.

Signs You Need a Replacement 2015 Optima Engine

• Knock from the bottom end that gets worse with mileage, classic Theta II bearing wear
• Low oil pressure light at idle on a warm engine, bearing wear or oil pump wear
• Loss of power and check engine light, turbocharger failure on the 2.0L Turbo
• Blue smoke on startup or under load, valve seal wear or piston ring wear
• Excessive oil consumption beyond 1 quart per 1,000 miles, ring or PCV system issue
• Coolant in oil, head gasket failure
• Hard starting and rough idle, GDI carbon buildup on intake valves (cleanable, not necessarily replacement)

Known 2015 Optima Engine Issues We Inspect Before Shipping

• Connecting rod bearing wear (Theta II), the highest-impact failure mode
• Oil pressure on a warm engine, recorded for every unit
• Timing chain stretch
• Turbocharger shaft play and oil seal condition (2.0L Turbo)
• High pressure fuel pump operation
• GDI intake valve carbon buildup noted

What Is Included, What Is Not Included

The 2015 Optima Theta II G4KJ and G4KH engines were also used in:

Transmission pairings: A6MF1 6-speed automatic (G4KJ 2.4 naturally aspirated), A6LF2 6-speed automatic (G4KH 2.0 turbo). Tell us your transmission and we confirm bell-housing and harness compatibility.

Not sure if this fits? Call (240) 301-0095 with your year, model, trim level, and engine code (found on the underhood emissions label). Our team confirms G4KJ versus G4KH variant before your order ships.

Every 2015 Optima engine we ship goes through this process:

• Compression test across all 4 cylinders, pressure per cylinder recorded
• Theta II rod bearing wear inspection, the most critical failure mode for this engine family
• Oil pressure recorded at idle and at 2,000 rpm
• Timing chain stretch checked
• Turbocharger inspection on 2.0L Turbo units (shaft play, oil seal, wastegate function)
• High pressure fuel pump function check
• GDI intake valve carbon level documented
• Engine code, year, and donor mileage when available

Where donor mileage is verified, it is shared. Where mileage cannot be confirmed, we disclose openly before payment. Full inspection notes are available on request.

Why Buy From Vaz Auto Solutions

• All 4 cylinders compression tested, results shared before order is confirmed
• Theta II rod bearing inspection on every unit, the critical wear point for this engine
• Oil pressure recorded for every unit, the leading indicator of bearing wear
• Engine code (G4KJ or G4KH) confirmed for your specific 2015 Optima trim
• Free crated freight to all 50 states, no hidden surcharges
• No core charge, keep your old engine
• 15 day replacement warranty on internal defects
• Hyundai-Kia experienced support team on the phone