BMW 8 Series 850i Engine ReplacementCompare Prices & Get Quotes

A BMW 8 Series 850i engine replacement typically costs £3,500-£5,500 for a used M70B50 unit, £5,500-£7,500 for a reconditioned engine, and £6,900-£9,500 for a fully rebuilt heritage-spec engine with 12-month warranty. Supply and fit costs add approximately £1,200-£2,000 depending on your location and the specialist's labour rates. The 850i's M70 V12 is a complex engine requiring specialist knowledge for correct fitment.

• Used engines: lowest cost, variable mileage and condition
• Reconditioned engines: mid-range, with replaced wearing components
• Rebuilt engines: highest cost, fully stripped and restored to OE spec
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The most common signs of M70B50 engine trouble in an 850i include: overheating or coolant loss (cooling system failure), rough running or loss of power (EML or ECU issues), blue smoke from the exhaust (valve guide wear), misfires or rough idle (ignition coil or crankshaft sensor failure), and oil leaks from valve covers or oil pan.

• Cooling issues: overheating, coolant leaks, temperature gauge fluctuations
• EML issues: rough running, loss of power, running on half cylinders
• Valve guide issues: blue smoke, excessive oil consumption
• Ignition issues: misfires, rough idle, poor performance
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Yes - if your BMW 8 Series 850i is otherwise in good condition, a replacement engine can extend its life significantly and preserve the value of this appreciating classic. With a typical E31 850i valued at £8,000-£25,000 depending on condition and transmission, a rebuilt engine at £6,900-£9,500 plus fitting represents a sound investment for well-maintained examples. Manual-transmission 850is (only 102 RHD examples ever made) command significant premiums, making engine replacement even more justifiable.

• Vehicle worth £15,000+: rebuilt engine is cost-effective
• Vehicle worth £8,000-£15,000: reconditioned is viable if keeping the car 2+ years
• Vehicle worth under £8,000: used engine or careful consideration of overall condition may be more sensible
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Most BMW 8 Series 850i engine replacements take 3-5 days for supply and fit at a specialist garage. Collection and delivery options are available nationwide, with most engines dispatched within 48-96 hours of order confirmation. The M70 V12's complexity and tight engine bay space make it a more time-consuming swap than simpler engines.

• Supply only: 48-96 hours dispatch
• Supply and fit: 3-5 days at specialist garage
• Nationwide collection/delivery available
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Yes - all rebuilt BMW 8 Series 850i engines supplied through EnginesMarket include a minimum 12-month unlimited-mileage warranty. Used engines typically come with a 3-6 month warranty depending on the supplier, and reconditioned engines often carry a 12-24 month warranty. Always confirm the exact warranty terms with your chosen supplier before purchasing.

• Rebuilt engines: 12+ months unlimited mileage
• Reconditioned engines: 12-24 months
• Used engines: 3-6 months typically
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The 850i (1990-1994) is powered by the M70B50 - a 5.0-litre V12 producing 296-300hp. The 850Ci (1992-1999) features the M73B54 - a 5.4-litre V12 producing 322hp. The 850CSi (1992-1996) is the high-performance variant with the S70B56 - a 5.6-litre V12 producing 375hp, available only with a 6-speed manual transmission. Engines are not interchangeable between these variants without significant modifications.

• 850i: 5.0L M70B50, 296-300hp, 1990-1994
• 850Ci: 5.4L M73B54, 322hp, 1992-1999
• 850CSi: 5.6L S70B56, 375hp, 1992-1996 (manual only)