Mercedes Benz G Class 250/300 Diesel Engine ReplacementCompare Prices & Get Quotes

A Mercedes G Class 250/300 Diesel engine replacement typically costs between £3,200 and £6,500 depending on engine code, condition type, and whether fitting is included. OM602 units start around £3,200, while OM606 turbodiesel units range from £4,500 to £6,500.

• Rebuilt OM603 (G 300 GD): £3,500-£5,500 supply only
• Rebuilt OM606 (G 300 Turbodiesel): £4,500-£6,500 supply only
• Used engines from breakers: £1,200-£4,000 but higher risk
• Labour for supply & fit adds £800-£1,500 to any engine price

The OM603's mechanical Bosch injection pump typically shows warning signs before complete failure - poor cold starting, white smoke on start-up, rough idle, and loss of power are the most common symptoms.

• Hard starting when cold that improves as the engine warms
• White or grey smoke from the exhaust, especially at idle
• Injector pump seal leaks (diesel weeping from the pump body)
• If the pump fails completely, the engine will not start at all

The OM606 is one of Mercedes' most over-engineered diesel engines and is legendary for longevity - many examples exceed 300,000 miles with basic maintenance. The timing chain is the main weak point, stretching approximately 1 degree per 100,000 miles.

• Regular oil changes (every 6,000-8,000 miles) are critical for chain life
• Timing chain inspection at 150,000 miles is recommended
• The engine responds well to specialist tuning (250-300hp achievable)
• With preventative maintenance, 300,000+ miles is realistic

Repair if the failure is isolated (e.g., injection pump seals on OM603, timing chain tensioner on OM606, vacuum pump on OM602). Replace if there's bottom end damage, bore scoring, or multiple major failures.

• OM603 injection pump calibration: £600-£1,000 - excellent value if caught early
• OM606 timing chain replacement: £1,200-£1,800 - do this preventatively
• Full OM603 rebuild: £3,500-£5,500 - for catastrophic failure or 180k+ miles
• Full OM606 rebuild: £4,500-£6,500 - still less than finding a replacement vehicle

Check your vehicle log book (V5C) for the engine number, which includes the engine code prefix (e.g., OM602, OM603, OM606).

• V5C log book shows full engine number with code prefix
• Engine code stamped on cylinder block (visible from under vehicle, left side)
• G 250 GD: OM602.931 (2.5L five-cylinder)
• G 300 GD: OM603.931 (3.0L six-cylinder naturally aspirated)
• G 300 Turbodiesel: OM606.964 (3.0L six-cylinder turbocharged)

We strongly advise against DIY fitting on a G Class diesel. The complex 4MATIC/4WD system, gearbox alignment, and injection pump timing requirements demand specialist equipment and expertise.

• 4MATIC transfer case alignment requires specialist knowledge
• Injection pump timing requires precise calibration tools (OM603/OM606)
• Engine and gearbox must be separated correctly to avoid damaging the torque converter
• Specialist supply & fit costs £800-£1,500 - worth every penny for these classics

Every engine supplied through EnginesMarket carries a minimum 12-month unlimited mileage warranty, with many specialists offering 24-month coverage on OM606 rebuilds. This includes parts and labour for any manufacturing defect or installation error.

• 12-month unlimited mileage is the minimum standard
• OM606 rebuilds often include 24-month warranty due to their robust design
• All warranties cover parts, labour, and MOT compliance
• Extended warranties available at point of purchase