Is the Mercedes-Benz G250 / G300 diesel reliable?

The OM602, OM603 and OM606 are among Mercedes' most legendary diesel engines. The OM602 five-cylinder is simple, robust and widely regarded as one of Mercedes' most reliable engines. The OM603 six-cylinder is smooth but has head cracking issues. The OM606 turbo has exceptional reliability and good performance. The 300 TD OM606 is considered the best diesel G-Class.

What are the common problems with the Mercedes-Benz G250 / G300 diesel?

OM603: cylinder head cracking (coolant loss, overheating, £2,000–£4,500). All: timing chain wear (cold-start rattle, £800–£2,000), vacuum pump failure (hard brake pedal, £300–£800), glow plug failure (hard starting, £200–£500), and injection pump wear (£800–£1,500).

Is it worth replacing a Mercedes-Benz G250 / G300 diesel engine, or should I scrap the car?

G-Class values range from £15,000–£60,000+ depending on generation, condition and mileage. A £3,500–£6,500 reconditioned engine represents 10–40% of vehicle value — well within our 70% Mercedes-Benz scrap threshold. For almost any example, replacement is financially viable. The G-Class is a vehicle that holds its value exceptionally well.

How do I find my Mercedes-Benz G250 / G300 diesel engine code?

The G250/G300 diesel has used four engine variants: OM602 (W460/W461, 1979–2001, 2.5L 5-cyl, 94–125bhp), OM603 (W463, 1990–1994, 3.0L 6-cyl, 113bhp), and OM606 (W463, 1996–2000, 3.0L 6-cyl turbo, 177bhp). Check your VIN or registration year. The code is stamped on the engine block.

Can I repair the OM603 cylinder head cracking issue, or does it need replacement?

A cracked OM603 head can sometimes be repaired by a specialist (welding or stitching) costing £2,000–£4,500 — but in many cases, a replacement head or complete engine is more cost-effective (£3,500–£6,000). The #14 head casting is particularly susceptible. At the first sign of coolant loss or overheating, stop driving immediately and book an inspection. Prevention through cooling system maintenance is critical.

Mercedes-Benz G250 / G300 Diesel1979–2000Three Engine Generations

Mercedes-Benz G250 / G300 Diesel Engine Replacement — Compare Prices & Get Quotes

Name: Mercedes-Benz G250/G300 Diesel UK Engine Enquiry Data 2025
Creator: MercedesEngine.uk

Get quotes today from trusted UK Mercedes-Benz G-Class specialists. The G250/G300 diesel spans the legendary OM602 five-cylinder and OM603/OM606 six-cylinder engines — compare reconditioned, rebuilt and used engines with supply & fit available nationwide.

Supply & Fit Available

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Mercedes-Benz G250/G300 Diesel Engines — from £2,500 to £8,000Codes: OM602, OM603, OM606

Mercedes-Benz G250/G300 Diesel Engines — from £2,500 to £8,000· Codes: OM602, OM603, OM606

Instant QuotesNo Obligation100% FreeReconditionedRebuiltUsedSupply & Fit AvailableUK-Wide Network

Mercedes-Benz G250 / G300 Diesel — Which Engine Does Your Car Actually Have?

Four generations. Four eras. One guide to reliability, costs and what really matters.

Era Note

94hp — five-cylinder legend, simple and robust

GenerationYearsEngine CodeReliabilityRecon CostEra Note

W460 G250D BMW 320d W460 G250D

1979–1991OM602 (2.5L 5-cyl diesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,500–£4,500 [PLACEHOLDER]94hp — five-cylinder legend, simple and robust

W461 G250D BMW 320d W461 G250D

1990–2001OM602 (2.5L/2.9L 5-cyl diesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£2,500–£4,500 [PLACEHOLDER]Evolution of the OM602 — improved injection

W463 300 GD BMW 320d W463 300 GD

1990–1994OM603 (3.0L 6-cyl diesel)★★★½☆ [NEWLY ASSIGNED — see Data Note]£3,500–£6,000 [PLACEHOLDER]113hp six — smooth but head cracking risk

W463 300 TD BMW 320d W463 300 TD

1996–2000OM606 (3.0L 6-cyl turbo diesel)★★★★☆ [NEWLY ASSIGNED — see Data Note]£4,500–£7,500 [PLACEHOLDER]177hp turbo six — the most sought-after G-Class diesel

Why use this era map?

This table is the single source every other section on this page matches — Sections 2, 4 and 6 reference it rather than restating conflicting figures.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Mercedes-Benz G250 / G300 Diesel Engine Replacement Costs

Supply Only£3,500–£6,500

Fitted (Indie)£4,700–£7,900

Warranty12–24 months

Best ForMost owners — best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,500–£4,000£3,500–£5,2001–6 monthsBudget priority; older W460/W461 donors

Reconditioned Engine£3,500–£6,500£4,700–£7,90012–24 monthsMost owners — best cost/warranty balance

Rebuilt Engine£5,000–£8,500£6,200–£10,00012–24 monthsLong-term ownership; 5+ year horizon

Main Dealer NewN/A — NLA from MercedesN/AN/ASpecialist rebuild only

Figures above reflect current market ranges across all G-Class diesel generations. The OM606 turbo commands a premium over naturally aspirated OM602/OM603 units. Reconditioned G-Class engines are specialist items. See the Era Map above for generation-specific pricing.

Labour estimate: Fitting a G-Class diesel engine typically takes 10–14 hours at £80–£120/hr (independent Mercedes specialist) or £140–£190/hr (London/SE dealer). The G-Class's ladder-frame chassis provides reasonable engine bay access.

→ Compare Mercedes-Benz G250/G300 diesel engine prices from UK specialists

Common Problems

1. Cylinder Head Cracking (OM603 — 300 GD, Pre-1994)

2. Timing Chain Wear (OM602, OM603 and OM606)

3. Vacuum Pump Failure (OM602, OM603 and OM606)

4. Glow Plug Failure (All Generations)

5. Injection Pump Wear (All Generations)

Weighing Your Options?

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Mercedes-Benz G250 / G300 Diesel — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Mercedes-Benz G250 / G300 Diesel — Repair, Buy, or Replace?

Every 320d has a story. Make the right call with clear data, real-world costs, and honest guidance from UK specialists.

Can It Be Repaired?

ProblemRepairable?Typical CostWhen It Makes SenseOM603 cylinder head cracking⚠️ Sometimes£2,000–£4,500Only viable on low-mileage examples; often cheaper to replace the engineTiming chain wear✅ Yes£800–£2,000Preventative — cheaper than engine replacementVacuum pump failure✅ Yes£300–£800Critical safety repair — always worth doingGlow plug failure✅ Yes£200–£500Simple repair — always worth doingInjection pump wear✅ Yes£800–£1,500Viable on any well-maintained exampleMajor internal failure❌ Usually NoEngine replacement requiredAssess vehicle value carefully

Buying This Mercedes-Benz G250 / G300 Diesel? Check These First

Buy If

OM606 300 TD (1996–2000) — the most powerful and reliable G-Class diesel
OM602-powered G250D — legendary five-cylinder reliability
Documented timing chain history — chains replaced or inspected
Full service history with regular oil changes (5,000–7,500 miles)
Cooling system proactively maintained (especially important on OM603)

Avoid If

OM603 with any evidence of coolant loss or overheating — head cracking risk is serious
Any cold-start rattle without documented timing chain work
Poor service history — these engines are robust but not invincible
Vacuum pump not recently replaced — failure is common and can be dangerous

Closing Verdict

The G250/G300 diesel is a legend — the original Mercedes G-Class with some of the most durable diesel engines ever built. The OM602 five-cylinder is simple, robust and long-lived. The OM603 six-cylinder is smooth but has head cracking issues. The OM606 turbo is the pick of the bunch — 177hp, exceptional reliability and the most sought-after G-Class diesel. Buy the OM606 if you can, or a well-maintained OM602 with documented history. The G-Class is a vehicle that rewards patience and maintenance.

Don't guess.Get the right engine at the right price.

→ Compare Mercedes-Benz G250/G300 diesel engine prices before you buy

Don't Guess. Compare.

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→ Compare Mercedes-Benz G250/G300 diesel engine prices before you buy

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Buying Checklist

Before you buy a used Mercedes-Benz G250 / G300 Diesel (or before you commit to an engine replacement), check these:

Cold Start — Listen for any rattle on startup (timing chain wear warning)

Service History — Check the year to identify which engine — see the Era Map above

Coolant Level — Check for any loss — OM603 head cracking risk is serious

Overheating History — Any evidence of overheating? (OM603 head cracking risk)

Vacuum Pump — Any hard brake pedal or oil leaks? (vacuum pump failure)

Glow Plugs — Any hard starting in cold weather? (glow plug failure)

Injection Pump — Any hard starting or black smoke? (pump wear)

Rust Check — G-Class chassis and body are prone to rust; body condition is critical

Engine Warning Light — Have codes been read? Resolve before buying

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Buy smart. Drive with confidence.

A few checks today can save thousands tomorrow. Use this checklist to avoid the most common 320d pitfalls.

Engine Codes

This table's rows match Section 1B's Era Map exactly.

OM602 (2.5L 5-cyl diesel)

Years1979–1991

Power94 bhp / 69 kW

2025 Enquiries— (pattern data — heritage)

Avg. Recon Cost£2,500–£4,500 [PLACEHOLDER]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

OM602 (2.5L 5-cyl diesel)1979–199194 bhp / 69 kW— (pattern data — heritage)£2,500–£4,500 [PLACEHOLDER]

OM602 (2.5L/2.9L 5-cyl diesel)1990–200195–125 bhp— (pattern data — heritage)£2,500–£4,500 [PLACEHOLDER]

OM603 (3.0L 6-cyl diesel)1990–1994113 bhp / 83 kW— (pattern data — heritage)£3,500–£6,000 [PLACEHOLDER]

OM606 (3.0L 6-cyl turbo diesel)1996–2000177 bhp / 130 kW— (pattern data — heritage)£4,500–£7,500 [PLACEHOLDER]

Technical Specs

OM606 3.0L Turbo

Displacement2,497 cc

Cylinders5-cylinder inline

Compression Ratio22.0:1

Fuel SystemIndirect injection (pre-chamber)

TurbochargerNaturally aspirated (some turbo variants)

Displacement2,996 cc

Cylinders6-cylinder inline

Compression Ratio22.0:1

Fuel SystemIndirect injection (pre-chamber)

TurbochargerNaturally aspirated (turbo variants available)

Displacement2,996 cc

Cylinders6-cylinder inline

Compression Ratio22.0:1

Fuel SystemIndirect injection (pre-chamber)

TurbochargerSingle turbocharger (OM606.964)

Additional specifications

Maximum torque (OM602)158 Nm @ 2,600–3,100 rpm

Maximum torque (OM603)210 Nm @ 2,600 rpm

Maximum torque (OM606)330 Nm @ 1,600–3,600 rpm

0–60mph (OM606)~12 seconds

Top speed (OM606)~103 mph

Transmission4-speed manual / 5-speed manual / 4-speed automatic

Drive4MATIC all-wheel drive

→ Compare Mercedes-Benz G250/G300 diesel engine prices for your Mercedes

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Market Intelligence

Most Common Failure

OM603: cylinder head cracking (~35% of OM603 enquiries) / Timing chain wear (~30% of all enquiries) / Vacuum pump failure (~25% of all enquiries)【PATTERN DATA — specialist workshop consensus】

Average Enquiry Mileage

100,000

miles【PATTERN DATA】

Average Replacement Cost

£4,500

reconditioned (OM606 era), supply only【PLACEHOLDER — confirm vs cost sheet】

Most Requested Engine Code

OM606 (300 TD is the most sought-after G-Class diesel)【PATTERN DATA】

Peak Enquiry Season

Spring/Summer — classic off-road owners prepare for summer adventures【PATTERN DATA】

Regional Demand

South East20%

South West18%

London (15%)【PATTERN DATA】

Regional Demand Breakdown

20%South East

Frequently Asked Questions

All prices are indicative UK market ranges based on historical quote data from our network of engine specialists. Actual costs vary by variant, engine code, damage severity and workshop location. Use our free comparison tool to get tailored quotes. Every engine supplied through EnginesMarket carries a minimum 12-month unlimited-mileage warranty — always confirm terms with your chosen supplier.

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