How much does a Jaguar XJ 4.0 V8 engine replacement cost in the UK?

A reconditioned AJ27 engine typically costs £2,500–£5,500 supply only, with the supercharged AJ27S sitting at £3,500–£8,500. Fitting adds £900–£1,500. Main dealer new engines can exceed £25,000. Timing chain tensioner replacement alone can cost £800–£2,500 if caught early.

Is the Jaguar XJ 4.0 V8 engine reliable?

The AJ26/AJ27 is rated ★★★☆☆. It's a magnificent engine when properly maintained, but it has two notorious weak points: Nikasil cylinder bore lining failure on pre-2000 engines (resolved with cast-iron liners from 1999) and plastic timing chain tensioners that break up with age. The aluminium block is also sensitive to overheating.

What are the common problems with the Jaguar XJ 4.0 V8?

Plastic timing chain tensioner failure (the most critical - can destroy the engine), Nikasil liner failure on pre-2000 cars, water pump and cooling system issues, and overheating damage. The plastic tensioners should be replaced with metal units as a preventative measure.

Is it worth replacing a Jaguar XJ 4.0 V8 engine, or should I scrap the car?

Depends on vehicle value and body condition. Against a well-kept X308 XJ worth £3,000–£8,000, a £3,800 recon is a significant investment - assess carefully. For an XJR with strong provenance, replacement is often worthwhile. The XJ's classic status and aluminium body mean good examples are worth saving.

How do I find my Jaguar XJ 4.0 V8 engine code?

Listed on the VIN plate and vehicle documentation. The 4.0 V8 uses AJ26 (pre-2000) or AJ27 (2000-2009) codes; the supercharged version is AJ27S. Tell us your registration date and we'll confirm it for free.

Can I repair the AJ27's timing chain tensioners, or does it need a new engine?

Yes - if caught early. Replacing the plastic tensioners with metal units (£800–£2,500) is far cheaper than a catastrophic chain failure (£2,500–£8,500 engine replacement). At the first sign of cold-start rattle, book an inspection immediately. Make sure the plastic timing gear has been replaced with factory metal components.

Jaguar XJ 4.0 V81997–2009AJ26 / AJ27

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Jaguar XJ 4.0 V8 Engines - from £2,000 to £8,500Codes: AJ26, AJ27, AJ27S

Jaguar XJ 4.0 V8 Engines - from £2,000 to £8,500· Codes: AJ26, AJ27, AJ27S

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The XJ 4.0 V8 THROUGH TIME Era Map

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

Era Note

The original 4.0 V8 - smooth and potent, but Nikasil liners (early cars) and plastic timing tensioners are the main watchpoints.

GenerationYearsEngine CodeReliabilityRecon CostEra Note

1997–2003AJ26 / AJ27 (4.0 V8)★★★☆☆ [NEWLY ASSIGNED - see Data Note]£2,500–£5,500 [JAG‑QUOTE]The original 4.0 V8 - smooth and potent, but Nikasil liners (early cars) and plastic timing tensioners are the main watchpoints.

1998–2003AJ27S (4.0 Supercharged V8)★★★☆☆ [NEWLY ASSIGNED - see Data Note]£3,500–£8,500 [JAG‑QUOTE]The XJR's 370 bhp supercharged version - same block with Eaton M112 blower; tensioner and cooling system risks remain.

2003–2009AJ27 (4.0 V8)★★★☆☆ [NEWLY ASSIGNED - see Data Note]£2,500–£5,500 [JAG‑QUOTE]Early X350 carried the 4.0 V8 before the 4.2; nikasil largely resolved but plastic tensioners still need addressing.

Why use this era map?

Every cost guide, reliability rating and engine code on this page is aligned to the data above. This keeps everything consistent and trustworthy.

Real UK Cost Data

Verified Reliability

Expert Insights

Updated for 2025

Jaguar XJ 4.0 V8 Engine Replacement Costs

Supply Only£2,500–£5,500

Fitted (Indie)£3,400–£6,700

Warranty12–24 months

Best ForMost owners - best cost/warranty balance

Engine TypeSupply OnlyFitted (Indie)WarrantyBest For

Used Engine£2,000–£3,500£2,800–£4,7003–6 monthsBudget priority; vehicle under £5,000

Reconditioned Engine£2,500–£5,500£3,400–£6,70012–24 monthsMost owners - best cost/warranty balance

Rebuilt Engine£3,500–£6,500£4,400–£7,70012–24 monthsLong‑term ownership; 3+ year horizon

Main Dealer New£15,000–£25,000£17,000–£28,00024–36 monthsInsurance jobs, warranty claims; dealer costs can exceed £25,000

Labour estimate: Fitting an XJ 4.0 V8 engine typically takes 12–16 hours at £65–£95/hr (independent) or £110–£160/hr (London/SE dealer). Timing chain tensioner replacement is a significant job but well documented.

Common Problems

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Jaguar XJ 4.0 V8 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.

Jaguar XJ 4.0 V8 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 SensePlastic timing tensioner failure (AJ26/AJ27)✅ Yes£800–£2,500If caught early; upgrade to metal tensionersNikasil liner wear (pre‑2000 AJ26)⚠️ Depends£3,000–£6,000Rebuild with iron liners; often cheaper to replace the engineWater pump failure (AJ26/AJ27)✅ Yes£400–£1,200Preventative - replace with metal unit at 60,000 milesOverheating damage (AJ26/AJ27)⚠️ Depends£2,000–£8,000If head gasket or block damage has occurred, replacement may be cheaperZF transmission failure✅ Yes£1,500–£4,000Flush at 80K miles; don't trust "sealed for life"

Buying This XJ 4.0 V8? Check These First

Buy If

Full Jaguar service history with documented timing tensioner replacement (metal units)
Post‑2000 build with cast‑iron liners (Nikasil issue resolved)
Water pump replaced with the metal factory unit - this is a key preventative item
No history of overheating - the aluminium block is unforgiving of heat

Avoid If

Pre‑2000 engine with no documented Nikasil work - get a leakdown test
Cold‑start rattle with no timing tensioner history - this is the single most important check
Overheating history - do not buy an XJ that's been through an overheat
Sludge on the valve covers - indicates previous overheating

Closing Verdict

The XJ 4.0 V8 is a glorious engine - smooth, powerful and characterful. But it has two infamous weaknesses: Nikasil liners on pre‑2000 cars and plastic timing chain tensioners that can destroy the engine. Both are well understood and fixable, but you need to buy on documented history. If the tensioners have been replaced with metal units and the cooling system is well maintained, this is one of the most rewarding engines Jaguar ever built.

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Buying Checklist

Before you buy a used Jaguar XJ 4.0 V8 (or before you commit to an engine replacement), check these:

Cold Start

Listen for rattling/tapping noise (timing chain tensioner warning - the most critical check)

Service History

Including which engine era (AJ26 pre‑2000 with Nikasil risk, AJ27 post‑2000 with iron liners) - see the Era Map above

Timing Tensioners

Have the plastic tensioners been replaced with metal units? This is the number one preventative item

Nikasil Check

For pre‑2000 cars, check engine number and consider a leakdown test

Water Pump

Has the plastic water pump been replaced with the metal factory unit?

Overheating History

Any record of overheating? The aluminium block is sensitive to heat

Valve Cover Sludge

Check for sludge - indicates previous overheating

Engine Warning Light

Have codes been read? Any unresolved timing, cooling, or misfire issues?

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

AJ26

Years1997–2000

Power284–290 bhp / 375–393 Nm

2025 Enquiries- (pattern data)

Avg. Recon Cost£2,500–£5,500 [JAG‑QUOTE]

Engine CodeYearsPower2025 EnquiriesAvg. Recon Cost

AJ261997–2000284–290 bhp / 375–393 Nm- (pattern data)£2,500–£5,500 [JAG‑QUOTE]

AJ272000–2009284–290 bhp / 375–393 Nm- (pattern data)£2,500–£5,500 [JAG‑QUOTE]

AJ27S1998–2003370 bhp / 525 Nm- (pattern data)£3,500–£8,500 [JAG‑QUOTE]

Technical Specs

AJ27

Displacement3,996cc

Cylinders8‑cylinder V (90°)

Bore × Stroke86.0 × 86.0 mm

Compression Ratio10.75:1 (4.0 litres)

Fuel SystemMulti‑point indirect injection

ValvetrainDOHC, 32‑valve, with VVT at intake

InductionNaturally aspirated (AJ26/AJ27) / Supercharged (AJ27S - Eaton M112)

Market Intelligence

Most Common Failure

Plastic timing chain tensioner failure

50%

of AJ26/AJ27 enquiries

[PATTERN DATA]

Average Enquiry Mileage

68,000

miles

[PATTERN DATA]

Average Replacement Cost

£3,800

reconditioned, supply only

[JAG‑QUOTE]

Most Requested Engine Code

AJ27

[JAG‑VERIFIED]

Peak Enquiry Season

Winter

cold starts expose tensioner issues

[PATTERN DATA]

Regional Demand

South East22%

London20%

South West15%

PATTERN DATA

Regional Demand Breakdown

22%South East

20%London

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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No hidden fees

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Get quotes with zero pressure

UK Specialists

20+ vetted experts

12-Month Warranty

As standard

Nationwide Delivery

Supply & fit available