Deep knock from the bottom end and oil light at hot idle
- Make and model
- Renault Megane III
- Year
- 2012
- Engine
- 1.5 dCi (K9K)
- Fuel
- Diesel
- Mileage
- 196,000 km
Customer complaint
A deep knock that gets louder as the engine warms up and when accelerating. The oil pressure light flickers at idle after a long drive. Serviced every 30,000 km, oil rarely checked.
Fault codes
No fault codes stored.
Measurements and live data
| Parameter / measurement | Measured | Expected |
|---|---|---|
| Oil pressure, hot idle (mechanical gauge) | 0.6 bar | typically above 1.0 bar |
| Oil pressure, hot, 2,000 rpm | 1.8 bar | typically above 2.5 bar |
| Oil level and condition | 5 mm above max, thin, smells of diesel | between min and max |
Tests performed
- Stethoscope low on the block, engine warmDeep knock rising with rpm, loudest around cylinders 2 and 3
- Oil filter cut openCopper-coloured bearing material in the pleats
- Sump removed, big-end caps checkedCyl. 2 big-end shell spun and scored, crank journal marked
Solution
Root cause
Big-end bearing on cylinder 2 spun after long oil intervals with oil diluted by diesel from interrupted particulate filter regenerations.
Repair
The crank journal was too damaged to polish, so a reconditioned short engine went in with a new oil pump, oil and filter, and a flushed oil cooler. Forced a particulate filter regeneration and set a 10,000 km oil change interval.
Parts
Reconditioned short engine, oil pump, gaskets, oil and filter
Labour time
14 h
Lesson learned
On this engine a rising oil level is bad news: diesel in the oil kills the big ends. Check the dipstick at every visit.
Training case: the usual fix for this fault, not a confirmed repair on a specific car.
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