Mercedes-Benz AMG GT S / GT C Engine Replacement Compare Prices & Get Quotes

A replacement M178 engine for a GT S or GT C typically costs between £4,500 and £16,500 depending on condition. Used units start from £4,500-£8,500, reconditioned from £8,000-£13,500, and fully rebuilt from £8,500-£16,500. Labour for supply & fit adds £800-£1,500 for AMG-specialist work.

• Used M178 LS1 (GT S): £4,500-£8,000
• Rebuilt M178 (GT C): £9,000-£16,500
• Supply & fit adds £800-£1,500

Both the GT S and GT C use the M178 engine, which has a timing chain, not a belt. However, the M178 is known for timing chain stretch on higher-mileage units - a metallic rattling noise on cold start is the classic warning sign. Mercedes issued a service campaign (2021-03B) addressing timing chain guide wear on early M178 engines.

• M178: timing chain - durable but stretch is a known issue
• Chain stretch common at 50k-80k miles
• Regular oil changes are critical for chain longevity

Common signs of engine problems in the GT S and GT C include: a rattling noise on cold start (timing chain stretch), loss of power or limp mode (turbo actuator failure), white steam from the engine bay or low coolant warnings (crossover pipe leak), and blue smoke on startup or after overrun (valve stem seal failure). If you experience any of these, have the car inspected immediately.

• Rattling on cold start - timing chain stretch
• Loss of power - turbo actuator or boost leak
• Coolant loss - hot-vee crossover pipe crack

It depends on the car's condition and mileage. A GT S or GT C is typically worth £35,000-£80,000 - a rebuilt M178 engine (£8,500-£16,500) is usually well within the car's value and can be a worthwhile investment if the car is in good condition. For lower-value examples or those with multiple issues, a specialist repair (timing chain, turbo actuator, crossover pipe) may be more economical than a full replacement.

• Vehicle worth £35,000-£50,000: rebuilt engine viable for good condition cars
• Vehicle worth £50,000+: rebuilt engine usually justifies cost
• Preventative repairs: often more economical than full replacement

Both the GT S and GT C use the same M178 4.0-litre V8 biturbo engine architecture, but with different power outputs and hardware. The GT S uses the M178 LS1 producing 510-522 hp with 650 Nm torque. The GT C uses the M178 producing 550-557 hp with 680 Nm torque - an increase achieved through revised turbochargers, a different ECU calibration, and a unique intake manifold. The GT C also features a wider rear track and active rear-axle steering, but the engine block and internals are largely shared.

• GT S (M178 LS1): 510-522 hp, 650 Nm
• GT C (M178): 550-557 hp, 680 Nm
• Same 4.0L V8 architecture, different turbos and ECU calibration

Power loss in the GT S and GT C is most commonly caused by turbo actuator failure, which sends the car into limp mode. Other causes include boost leaks from the hot-vee intercooler system, timing chain stretch causing cam timing drift, and carbon buildup on intake valves from the direct injection system. A diagnostic check with Mercedes STAR or compatible equipment is essential to identify the exact cause.

• Turbo actuator failure - most common cause of limp mode
• Timing chain stretch - power loss + rattling
• Boost leaks - from intercooler or charge air pipes