The single most enquired-about failure on this entire site. What causes it, the early warning sign almost everyone ignores, how to reduce your risk, and an honest answer on whether it's worth fixing.
306DT crankshaft bearing failure is a catastrophic, well-documented weak point - but on almost every vehicle it's fitted to, replacement is still the financially sound choice.
Full symptom progression, root cause, prevention and complete cost breakdown below.
The failure rarely arrives without warning. It progresses through a fairly predictable sequence over weeks or months, and where you catch it in that sequence is the single biggest factor in what it ends up costing you.
If you recognise yourself at any point in that sequence, the practical advice is the same: get it listened to by a specialist this week, not next month. See our broader engine knocking noise guide if you're not yet certain this is what you're hearing, or the 306DT-specific knocking diagnosis page for a narrower look at this exact engine.
The 306DT's crankshaft main bearings use a tin-aluminium coating designed to handle the loads of a high-torque V6 diesel. Over time and mileage, this coating is prone to fatigue - a known characteristic of the design rather than a fault specific to any particular batch or production run [EM-INTERVIEW]. Once the coating begins to break down, metal-on-metal contact accelerates rapidly, and bearing material entering the oil system contaminates the entire lubrication circuit - which is precisely why the failure, once it moves past the early cold-start-knock stage, tends to progress from "concerning noise" to "engine out of action" faster than most owners expect. The contamination is also why the turbo frequently suffers secondary damage; oil carrying metal particulate reaches the turbo bearings long before the fault is visually obvious anywhere else. Real mileage-at-failure distribution, drawn from our full dataset rather than a single average figure, is charted on our 306DT failure rate data page.
| Model | Badge | Years | Risk Level |
|---|---|---|---|
| Discovery 4 | TDV6 / SDV6 | 2009–2016 | High - most-enquired host |
| Range Rover Sport L494 | SDV6 | 2013–2020 | Documented, manageable |
| Range Rover L405 | TDV6 / SDV6 | 2012–2020 | Documented, manageable |
| Range Rover Sport L320 | SDV6 | 2009–2013 | Higher risk - older host |
| Velar L560 | D300 | 2017–2020 | Pre-2021 units only |
Vehicles with documented intervals at or ahead of schedule, using the correct specification oil, show a materially lower incidence in our enquiry data than those with extended or undocumented intervals.
Frequent short journeys that never let the engine reach full operating temperature contribute to oil degradation faster than motorway-weighted use, compounding the bearing wear risk over time.
Risk is concentrated between 80,000 and 140,000 miles rather than rising steadily with age - vehicles that pass through this band without symptoms rarely develop the fault afterward.
A specialist starts the engine from stone cold and listens specifically for the bearing knock in the first 10–15 seconds - this alone catches the large majority of early cases.
A sample sent for laboratory analysis can detect metal particulate before the noise becomes obvious, catching the failure at its earliest and cheapest-to-address stage - the same early-detection principle covered on our 276DT oil pump failure page, this engine's predecessor.
A drop in oil pressure at idle, particularly once fully warm, is a strong secondary confirmation alongside the cold-start knock and is straightforward for any competent specialist to check.
Caught early versus caught late - the gap is the whole argument for prompt diagnosis.
| Stage | Used S&F | Reconditioned S&F | Rebuilt S&F | Main Dealer Est. |
|---|---|---|---|---|
| Caught early (cold-start knock only) | £3,500–£5,500 | £6,500–£9,500 [EM-QUOTE] | £7,500–£11,000 | £12,000–£18,000 |
| Catastrophic (bearing failed, contamination present) | Not recommended | £8,500–£11,500 | Not viable | £14,000–£20,000 |
R&R labour 15–20 hours [EM-QUOTE]. Typical independent-specialist fitted premium over supply-only: £975–£1,300.
You cannot eliminate the risk of this failure entirely - it's a design-level characteristic, not a maintenance failure on the owner's part. But you can meaningfully reduce both the likelihood and the severity if it does occur. Keep oil changes at or ahead of the manufacturer interval, use the correct specification oil every time rather than whatever's cheapest, and - most importantly - treat any new cold-start noise as worth investigating within days rather than months. An annual oil analysis, costing a fraction of a diagnostic visit, can flag bearing wear before it's audible at all. None of this guarantees you'll avoid the fault, but owners who follow this pattern consistently report catching it, when it happens, at the cheap end of the cost table above rather than the expensive end.
A knocking or rattling noise on cold start that quietens or disappears once the engine warms up. This is the earliest and most reliable warning sign, and it should never be dismissed as normal diesel clatter.
In some cases a bottom-end rebuild is possible, typically £5,500-£7,000, but once bearing material has contaminated the oil system a full reconditioned engine is usually the more reliable long-term option, at £6,500-£9,500 supply and fit.
On almost every Discovery 4, Range Rover Sport and Range Rover L405 fitted with this engine, yes. Vehicle values in this range typically sit between £10,000 and £40,000, comfortably clearing our 60% repair-to-value threshold even at the top of the reconditioned cost range.
The bearing surface uses a tin-aluminium coating that is prone to fatigue over time, particularly where oil change intervals have been extended or oil quality has been inconsistent. It is a design-level weak point rather than a build defect specific to any batch.
You cannot eliminate the risk entirely, but strict adherence to oil change intervals with the correct specification oil, and prompt investigation of any cold-start noise, meaningfully reduces both the likelihood and the severity if it does occur.
980 Real EnquiriesThis exact failure analysed across our 2025 UK data.
Honest Severity RatingWe call this Catastrophic and mean it - same standard applied to every fault on this site.
12 Vetted JLR SpecialistsEvery recommendation routes to a specialist who rebuilds these engines regularly.
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