BMW 3 Series E30Saloon/Coupé/Convertible1982–1994
Every engine fitted to the E30 — from the carburetted 1.8-litre M10 four-cylinder to the 2.5-litre M20 straight-six, plus the M3's iconic S14 and BMW's first-ever diesel.
Real UK replacement costs, honest reliability data, and the timing belt and cooling system weaknesses that define this classic generation.
Backed by real UK E30 enquiries in 2025 [BMW-VERIFIED].
Engine Database
Every engine fitted to the E30 — from the entry-level four-cylinder to the range-topping M3 and the diesel that started BMW's diesel journey.
Overview
The BMW E30, produced from 1982 to 1994, is the second generation of the 3 Series and one of the most beloved BMWs ever built. It was the first 3 Series to be offered in four-door saloon and estate ("Touring") body styles, alongside the two-door saloon and convertible.
The E30 also introduced BMW's first diesel engine (M21) and the first all-wheel-drive 3 Series (325iX). The M3, powered by the high-revving S14 four-cylinder, established BMW's M division as a force in motorsport.
Key Facts
Market Intelligence
The E30 generated real UK engine enquiries in 2025 [BMW-VERIFIED], with the M20B25 (325i) and S14 (M3) accounting for the majority of demand as these cars enter modern classic and collector territory.
04Best & Worst Engines
Best Diesel Overall
M21D24 (324d, 1985–1990) – "BMW's first diesel is a rugged six-cylinder unit that delivers 86 hp and 153 Nm of torque – modest by modern standards, but reliable and efficient. It was the only diesel option in the E30 range and remains a curio for collectors."
“”
Who it's for: buyers who want a slice of BMW diesel history and don't need performance.
Best Petrol Overall
M20B25 (325i, 1985–1991) – "The 2.5-litre straight-six is the E30's sweet spot – 171 hp of smooth, linear power with a sonorous exhaust note that defines the classic BMW six experience. No turbos, no complex electronics – just a well-sorted engine that rewards maintenance."
“”
Who it's for: buyers who want the definitive E30 driving experience.
Highest Risk
S14B23 (M3, 1986–1991) – "The M3's high-revving four-cylinder is a masterpiece, but it's also the most expensive E30 engine to maintain. Timing chain tensioner wear and expensive parts availability mean this is not an engine for the faint-hearted – a full rebuild can exceed £10,000."
“”
Who it's for: collectors and enthusiasts with deep pockets.
Most Expensive Failure
S14B23 Engine Rebuild – "The S14's individual throttle bodies, high-compression internals and limited parts supply make a full rebuild one of the most expensive bills in the classic BMW world – £5,000–£10,000 for a proper rebuild is not unusual."
“”
Who it's for: only buyers with a dedicated restoration budget.
Best Value
M42B18 (318is, 1989–1991) – "The 16-valve 1.8-litre four-cylinder delivers 136 hp with a 7,000 rpm redline – it's the sportiest four-cylinder E30, cheaper to run than the sixes, and genuinely fun to drive. Timing chain (not belt) and well-sorted injection make it a reliable choice."
“”
Who it's for: buyers who want E30 handling without the six-cylinder running costs.
Most Overlooked
M20B23 (323i, 1982–1986) – "The 2.3-litre straight-six was the range-topper before the 325i arrived – 150 hp, smooth and free-revving. Most buyers overlook it in favour of the 325i, but it's cheaper to buy and shares much of the same character."
“”
Who it's for: buyers who want six-cylinder E30 charm on a budget.
Best Diesel Overall
M21D24
(324d, 1985–1990) – "BMW's first diesel is a rugged six-cylinder unit that delivers 86 hp and 153 Nm of torque – modest by modern standards, but reliable and efficient. It was the only diesel option in the E30 range and remains a curio for collectors."
“”
Who it's for: buyers who want a slice of BMW diesel history and don't need performance.
Best Petrol Overall
M20B25
(325i, 1985–1991) – "The 2.5-litre straight-six is the E30's sweet spot – 171 hp of smooth, linear power with a sonorous exhaust note that defines the classic BMW six experience. No turbos, no complex electronics – just a well-sorted engine that rewards maintenance."
“”
Who it's for: buyers who want the definitive E30 driving experience.
Highest Risk
S14B23
(M3, 1986–1991) – "The M3's high-revving four-cylinder is a masterpiece, but it's also the most expensive E30 engine to maintain. Timing chain tensioner wear and expensive parts availability mean this is not an engine for the faint-hearted – a full rebuild can exceed £10,000."
“”
Who it's for: collectors and enthusiasts with deep pockets.
Most Expensive Failure
S14B23
Engine Rebuild – "The S14's individual throttle bodies, high-compression internals and limited parts supply make a full rebuild one of the most expensive bills in the classic BMW world – £5,000–£10,000 for a proper rebuild is not unusual."
“”
Who it's for: only buyers with a dedicated restoration budget.
Best Value
M42B18
(318is, 1989–1991) – "The 16-valve 1.8-litre four-cylinder delivers 136 hp with a 7,000 rpm redline – it's the sportiest four-cylinder E30, cheaper to run than the sixes, and genuinely fun to drive. Timing chain (not belt) and well-sorted injection make it a reliable choice."
“”
Who it's for: buyers who want E30 handling without the six-cylinder running costs.
Most Overlooked
M20B23 (323i, 1982–1986) – "The 2.3-litre straight-six was the range-topper before the 325i arrived – 150 hp, smooth and free-revving. Most buyers overlook it in favour of the 325i, but it's cheaper to buy and shares much of the same character."
“”
Who it's for: buyers who want six-cylinder E30 charm on a budget.
Engine
Typical Mileage
Common Major Failure
Repair Cost (Specialist)
Replacement Cost (Recon)
Ownership Verdict
Solid – bulletproof, cheap to run.Solid – simple, reliable four.
Best Value – sporty, reliable, chain-driven.Solid – six-cylinder charm, moderate costs.Overlooked – cheap entry to six-cylinder E30.Best Petrol – the definitive E30 engine.Watch – economical but an acquired taste.Expensive – collector's engine with collector's bills.Niche – BMW's first diesel; a curio.EngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership VerdictSolid – bulletproof, cheap to run.Solid – simple, reliable four.Best Value – sporty, reliable, chain-driven.Solid – six-cylinder charm, moderate costs.Overlooked – cheap entry to six-cylinder E30.Best Petrol – the definitive E30 engine.Watch – economical but an acquired taste.Expensive – collector's engine with collector's bills.Niche – BMW's first diesel; a curio.
The E30 rule
A £2,500–£5,000 M20B25 recon against a £4,000–£12,000 E30 325i sits at 21–125% of the car's value. On a sub-£5,000 example, that brushes our 70% BMW threshold – we'll honestly tell you to walk away unless the car is exceptional. Against a £10,000+ low-mileage example, the same recon drops to a routine 25–50% – a repair decision, not a financial one. For the M3, the economics are different – values are high enough that even a £10,000 rebuild is a viable investment on a £25,000+ car.
Key Takeaways
Which E30 Costs Least To Own?
M10B18 (316) – simple, bulletproof, cheap parts.
Which E30 Costs Most To Own?
S14B23 (M3) – high-performance four with expensive parts.
Which E30 Is Best Value?
M42B18 (318is) – four-cylinder fun with chain-driven reliability.
Timing
Belt Failure (M10, M40, M20 Engines)
Affected models:
All E30 four-cylinder (M10, M40) and six-cylinder (M20) petrol engines.
Typical failure mileage:
40,000–60,000 miles (interval-dependent).
Root cause:
The timing belt is a rubber component that degrades with age and mileage – if it fails, the pistons strike the valves, destroying the engine. This is the single most critical maintenance item on any M10, M40 or M20 engine. The M42 (318is) uses a timing chain, which is less prone to catastrophic failure.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£600–£1,000
£300–£600
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£8,000
£1,200–£2,500
Our Recommendation
If you own any E30 with an M10, M40 or M20 engine, treat the timing belt as a service item with a hard 40,000-mile or 4-year interval – £300–£600 now is dramatically cheaper than the £1,200+ replacement that follows a failure. Replace the water pump at the same time.
Cooling
System Vulnerabilities (All Petrol Engines)
Affected models:
All E30 petrol variants (all years).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The plastic radiator end tanks and water pump impeller degrade with age and heat cycling – coolant leaks are the first sign, followed by overheating and head gasket failure if ignored.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£800–£1,500
£400–£800
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£8,000
£1,200–£2,500
Our Recommendation
Replace the radiator, water pump and thermostat proactively at 60,000 miles – £400–£800 now is cheap insurance against a £1,200+ replacement. On a car over 20 years old, consider replacing all coolant hoses as well.
M20
Cylinder Head & Head Gasket Wear
Affected models:
E30 320i, 323i, 325i, 325e (M20 six-cylinder engines).
Typical failure mileage:
80,000–150,000 miles.
Root cause:
The M20 six-cylinder can suffer from head gasket failure, particularly if the cooling system has been neglected. Symptoms include coolant loss, oil in coolant, or coolant in oil – or external leaks from the head gasket.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,200–£2,000
£600–£1,200
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£8,000
£1,200–£2,500
Our Recommendation
If your M20 shows any signs of coolant loss or overheating, have a cylinder leak-down test performed immediately – a £600–£1,200 head gasket replacement is far cheaper than a £1,200+ engine replacement. Always use genuine BMW or high-quality gaskets.
M42
Timing Chain Tensioner Wear (318is)
Affected models:
E30 318is (M42B18), high-mileage examples.
Typical failure mileage:
80,000–120,000 miles.
Root cause:
The M42's timing chain tensioner can wear, causing chain rattle on cold start. If ignored, the chain can skip teeth and cause valve damage – though this is less common than belt failure on other E30 engines.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£800–£1,500
£400–£800
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£6,000
£2,000–£3,500
Our Recommendation
If your 318is exhibits any cold-start rattle, have the timing chain tensioner inspected immediately – a £400–£800 repair is far cheaper than a £2,000+ replacement. The M42 is otherwise a very reliable engine.
S14
Valve Adjustment & Timing Chain Tensioner (M3)
Affected models:
E30 M3 (S14B23), all years.
Typical failure mileage:
30,000–60,000 miles (valve adjustment interval).
Root cause:
The S14's high-revving nature demands regular valve clearance adjustments – neglected valves can cause poor performance and, in extreme cases, valve damage. The timing chain tensioner can also wear.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,500–£2,500
£800–£1,500
Catastrophic (Replacement)
Dealer
Specialist
£10,000–£15,000
£5,000–£10,000
Our Recommendation
If you own an E30 M3, treat valve adjustment as a sacred service item – £800–£1,500 every 30,000 miles is the cost of keeping this engine happy. Use a specialist who knows the S14; it is not a DIY job for the inexperienced.
VariantEngine Code
Used (Supply)
Reconditioned (Supply)
Rebuilt (Supply)
Labour HoursScope note: All variants listed are E30 only. The E30 was offered in multiple body styles – 2-door saloon, 4-door saloon, convertible and Touring (estate) – with engine availability varying by body style and market. The 325iX was the first BMW production car with all-wheel drive. The M3 is a separate model with the S14 engine.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Live FeedBMW 325i
M20B25
Birmingham
Timing belt enquiry5
enquiries
Updated MonthlyBMW M3
S14B23
LondonValve adjustment3
enquiries
Updated MonthlyBMW 318is
M42B18
ManchesterCold-start rattle2
enquiries
Updated MonthlyMost Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Scope note: All variants listed are E30 only. The E30 was offered in multiple body styles – 2-door saloon, 4-door saloon, convertible and Touring (estate) – with engine availability varying by body style and market. The 325iX was the first BMW production car with all-wheel drive. The M3 is a separate model with the S14 engine.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Live FeedBMW 325i
M20B25
BirminghamTiming belt enquiry5
enquiries
BMW M3
S14B23
LondonValve adjustment3
enquiries
BMW 318is
M42B18
ManchesterCold-start rattle2
enquiries
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