BMW 7 Series E23Saloon1977–1986
Every engine fitted to the E23 — from the 2.5-litre M30 four-cylinder that launched BMW's first 7 Series to the 3.5-litre M88 in the South African 745i and the turbocharged M102/M106 that redefined luxury performance.
Real UK replacement costs, honest reliability data, and the fuel injection and cooling system quirks that define this classic generation.
Backed by real UK E23 enquiries in 2025 [BMW-VERIFIED].
Engine Database
Every engine fitted to the E23 — from the entry-level carburetted four-cylinder to the range-topping M88-powered 745i SA.
Overview
The BMW E23, launched in May 1977, is the first generation of the 7 Series and the flagship of the BMW range. Designed by Paul Bracq and Manfred Rennen, it replaced the New Six (E3) sedans and established BMW's presence in the full-size luxury segment.
Initially powered by carburetted and fuel-injected M30 straight-six engines, the E23 introduced many electronic features for the first time in a BMW, including an on-board computer, service interval indicator, and a "check control" warning system. From 1980, turbocharged engines were available, and a rare South African variant used the M88/3 engine from the M1.
Key Facts
Market Intelligence
The E23 generated real UK engine enquiries in 2025 [BMW-VERIFIED], with the M30B32 (732i/733i) and M90/M30B34 (735i) accounting for the majority of demand as these cars enter classic collector territory.
04Best & Worst Engines
Best Petrol Overall
M30B34 (735i, 1982–1986) – "The later 3.4-litre M30 with Motronic injection delivers 218 PS of smooth, linear power with improved reliability over earlier L-Jetronic cars. The 'Big Six' is renowned for its durability – these engines regularly exceed 200,000 miles with proper maintenance. Cooling system and fuel injection are the only real demands."
“”
Who it's for: buyers who want the definitive E23 driving experience.
Highest Risk
M102/M106 (745i, turbocharged) – "The early turbocharged M30 engines are complex – the KKK turbocharger, charge-air cooling and fuel enrichment systems can be problematic. Parts are increasingly difficult to source, and specialist knowledge is essential. Boost pressure and fuel system issues can lead to catastrophic engine failure if ignored."
“”
Who it's for: only buyers who are comfortable with classic turbocharged systems and have a dedicated maintenance budget.
Most Expensive Failure
M88/3 (South African 745i) – "The M88/3 is a rare and valuable engine – essentially a detuned version of the M1's engine with individual throttle bodies and 286 PS. Parts are extremely expensive and specialist-only. A full rebuild can exceed £10,000."
“”
Who it's for: collectors and enthusiasts with very deep pockets.
Best Value
M30B28 (728i, 1979–1986) – "The 2.8-litre injected M30 delivers 184 PS with excellent economy for a large saloon. No turbocharger complexity, no carburettor to fiddle with – just a solid, reliable six-cylinder that will run forever with basic maintenance. It's the entry point to E23 ownership."
“”
Who it's for: buyers who want classic 7 Series presence with minimal maintenance headaches.
Most Overlooked
M30B32 (732i/733i, 1979–1986) – "The 3.2-litre engine is often overlooked in favour of the 735i, but it delivers 197 PS with virtually identical reliability and lower running costs. The Motronic injection on later cars is a significant upgrade over early L-Jetronic systems. It's the sweet spot of the naturally aspirated range."
“”
Who it's for: buyers who want six-cylinder refinement without the 735i's premium.
Best Petrol Overall
M30B34
(735i, 1982–1986) – "The later 3.4-litre M30 with Motronic injection delivers 218 PS of smooth, linear power with improved reliability over earlier L-Jetronic cars. The 'Big Six' is renowned for its durability – these engines regularly exceed 200,000 miles with proper maintenance. Cooling system and fuel injection are the only real demands."
“”
Who it's for: buyers who want the definitive E23 driving experience.
Highest Risk
M102/M106
(745i, turbocharged) – "The early turbocharged M30 engines are complex – the KKK turbocharger, charge-air cooling and fuel enrichment systems can be problematic. Parts are increasingly difficult to source, and specialist knowledge is essential. Boost pressure and fuel system issues can lead to catastrophic engine failure if ignored."
“”
Who it's for: only buyers who are comfortable with classic turbocharged systems and have a dedicated maintenance budget.
Most Expensive Failure
M88/3
(South African 745i) – "The M88/3 is a rare and valuable engine – essentially a detuned version of the M1's engine with individual throttle bodies and 286 PS. Parts are extremely expensive and specialist-only. A full rebuild can exceed £10,000."
“”
Who it's for: collectors and enthusiasts with very deep pockets.
Best Value
M30B28
(728i, 1979–1986) – "The 2.8-litre injected M30 delivers 184 PS with excellent economy for a large saloon. No turbocharger complexity, no carburettor to fiddle with – just a solid, reliable six-cylinder that will run forever with basic maintenance. It's the entry point to E23 ownership."
“”
Who it's for: buyers who want classic 7 Series presence with minimal maintenance headaches.
Most Overlooked
M30B32 (732i/733i, 1979–1986) – "The 3.2-litre engine is often overlooked in favour of the 735i, but it delivers 197 PS with virtually identical reliability and lower running costs. The Motronic injection on later cars is a significant upgrade over early L-Jetronic systems. It's the sweet spot of the naturally aspirated range."
“”
Who it's for: buyers who want six-cylinder refinement without the 735i's premium.
Engine
Typical Mileage
Common Major Failure
Repair Cost (Specialist)
Replacement Cost (Recon)
Ownership Verdict
Solid – the entry-level E23.Solid – carburetted six, simple but thirstier.
Solid – reliable injected six, best value.Solid – rare, carburetted 3.0.Best Value – the sweet spot of the range.Watch – US emissions equipment adds complexity.Collectable – the definitive early 735i.Best Petrol – the most refined naturally aspirated E23.Watch – complex turbo system; specialist-only.Watch – improved but still complex.Expensive – M1-derived engine; serious specialist territory.EngineTypical MileageCommon Major FailureRepair Cost (Specialist)Replacement Cost (Recon)Ownership VerdictSolid – the entry-level E23.Solid – carburetted six, simple but thirstier.Solid – reliable injected six, best value.Solid – rare, carburetted 3.0.Best Value – the sweet spot of the range.Watch – US emissions equipment adds complexity.Collectable – the definitive early 735i.Best Petrol – the most refined naturally aspirated E23.Watch – complex turbo system; specialist-only.Watch – improved but still complex.Expensive – M1-derived engine; serious specialist territory.
The E23 rule
A £2,500–£5,000 M30B32 recon against a £2,000–£8,000 E23 sits at 31–250% of the car's value. On a sub-£4,000 example, that brushes our 70% BMW threshold – we'll honestly tell you to walk away unless the car is exceptional. Against a £7,000+ low-mileage example, the same recon drops to a routine 36–71% – a repair decision, not a financial one. For the 745i, values are high enough that even a £8,000 M106 rebuild is often a viable investment on a £10,000+ car.
Key Takeaways
Which E23 Costs Least To Own?
M30B28 (728i) – simplest injected six, cheapest parts.
Which E23 Costs Most To Own?
M88/3 (South African 745i) – rare, complex, expensive parts.
Which E23 Is Best Value?
M30B32 (732i/733i) – the sweet spot between performance and running costs.
Cooling
System Vulnerabilities (All Engines)
Affected models:
All E23 petrol variants (1977–1986).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The cooling system is the Achilles heel of the E23 – radiators, water pumps and hoses degrade with age. Overheating can lead to head gasket failure on all M30 engines. The M30's iron block and aluminium head combination is sensitive to overheating; a warped head is a common consequence of neglected cooling maintenance.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£800–£1,500
£300–£700
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£8,000
£1,200–£2,500
Our Recommendation
On any E23, replace the radiator, water pump and thermostat proactively – £300–£700 now is cheap insurance against a £1,200+ replacement. The M30 engine is famously durable, but the cooling system will kill it if neglected. Use the correct BMW coolant and change it every two years.
Fuel
Injection System Issues (Injected Models)
Affected models:
E23 fuel-injected models (728i, 732i, 733i, 735i, 745i).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The early L-Jetronic systems (1979–1981) suffer from fuel distributor wear, injector clogging and vacuum leaks. The later Motronic systems (1982–1986) are more reliable but can suffer from DME (engine control unit) issues and faulty sensors. The combination relay that controls the fuel pump is a common failure point on all injected E23s.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£800–£1,500
£400–£1,000
Catastrophic (Replacement)
Dealer
Specialist
£4,000–£8,000
£1,500–£3,000
Our Recommendation
If your E23 has running issues, start with the fuel pump relay and grounds – a £50 repair is far cheaper than a £400+ injection rebuild. For L-Jetronic cars, have the injectors professionally cleaned. Motronic cars should have the DME checked for dry solder joints.
M30
Cylinder Head & Head Gasket Wear
Affected models:
All E23 M30-engined variants (all years).
Typical failure mileage:
80,000–150,000 miles.
Root cause:
The M30's iron block and aluminium cylinder head combination 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 M30 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 and have the head skimmed flat during replacement.
Turbocharger
& Fuel Enrichment Issues (745i)
Affected models:
E23 745i (M102, M106 turbocharged engines).
Typical failure mileage:
60,000–100,000 miles.
Root cause:
The early turbocharged M30 engines use a KKK turbocharger and complex fuel enrichment systems. Common issues include turbocharger bearing wear, wastegate actuator failure, fuel enrichment system leaks, and boost pressure inconsistencies. The M106's Motronic system was an improvement over the M102's Jetronic-based system but still requires specialist knowledge.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£2,000–£4,000
£800–£2,000
Catastrophic (Replacement)
Dealer
Specialist
£8,000–£12,000
£4,000–£7,000
Our Recommendation
If you own a 745i, have the turbocharger and fuel enrichment system inspected by a specialist who knows these engines – £800–£2,000 now is far cheaper than a £4,000+ replacement. Use only the correct grade of oil and allow the turbo to cool after hard driving. The M106 is an improvement but still demands respect.
4HP22
Automatic Transmission (All Models)
Affected models:
All E23 automatic variants (1977–1986).
Typical failure mileage:
80,000–150,000 miles.
Root cause:
The ZF 4HP22 automatic transmission can suffer from forward clutch failure (specifically the 'A' clutch), leading to slipping, harsh shifts and eventual loss of drive. This is a well-documented weakness of this transmission.
Tiered Cost Table
Preventative (Repair)
Dealer
Specialist
£1,500–£2,500
£800–£1,500
Catastrophic (Replacement)
Dealer
Specialist
£3,500–£5,000
£2,000–£4,000
Our Recommendation
If your E23 has any transmission hesitation or harsh shifts, have the transmission fluid and filter changed and the valve body inspected – £800–£1,500 now is far cheaper than a £2,000+ replacement. ZF have a replacement part for the forward A clutch issue. Consider a manual conversion if you want the most reliable option.
VariantEngine Code
Used (Supply)
Reconditioned (Supply)
Rebuilt (Supply)
Labour HoursScope note: All variants listed are E23 only. The E32 (1986–1994) is the successor generation with its own engine line-up – see the E32 Generation Page for those specifications. The 745i (SA) is a rare South African variant using the M88/3 engine from the BMW M1.
Most Requested Engines (2025)
Most Requested Variants
Average Replacement Cost
£1,200–£10,000 supply only .
[BMW-QUOTE]
Most Common Failures
Live FeedBMW 735i
M30B34
Birmingham
Overheating enquiry4
enquiries
Updated MonthlyBMW 745i
M106
LondonTurbocharger boost issue2
enquiries
Updated MonthlyBMW 732i
M30B32
ManchesterRough idle2
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 E23 only. The E32 (1986–1994) is the successor generation with its own engine line-up – see the E32 Generation Page for those specifications. The 745i (SA) is a rare South African variant using the M88/3 engine from the BMW M1.
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 735i
M30B34
BirminghamOverheating enquiry4
enquiries
BMW 745i
M106
LondonTurbocharger boost issue2
enquiries
BMW 732i
M30B32
ManchesterRough idle2
enquiries
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