BMW N46 Engine Reliability Guide
The BMW N46 is the 2.0-litre naturally aspirated four-cylinder petrol of 2004 to 2015 with Valvetronic and port injection: 118i, 120i, 316i, 318i, 320i, 520i, X1 sDrive18i, X3 2.0i and Z4 2.0i. Adequate rather than brilliant, economical, and mostly troubled by oil consumption and Valvetronic niggles rather than outright failures.
Quick verdict
The N46 is a sensible cheap-BMW engine if it does not smoke on a cold start. Oil consumption from valve stem seals and the crankcase breather is the defining habit, the timing chain wears but sits at the front and costs half an N47 job, and the Valvetronic sensor and water pump are the other predictable items. ULEZ-compliant petrol, which keeps 118i, 318i and X1 18i values steady. BMW brought it back into the 316i and 318i in 2010 to 2012 after the N43 experiment.
What is the BMW N46?
The N46 lives in the cheapest BMWs in the UK: E87 118i and 120i, E90 318i and 320i, E46 318i and 320i, first-generation X1 18i and E85 Z4 2.0i, mostly £1,500 to £5,000 with 90,000 to 170,000 miles. Confirm it is an N46 and not the direct-injection N43 of 2007 to 2011 (much worse injectors). Watch the exhaust on a cold start, check the oil level and ask about the crankcase breather and Valvetronic sensor.
| Full engine code | N46B20 |
|---|---|
| Configuration | I4 naturally aspirated petrol, Valvetronic, port injection |
| Production years | 2004-2015 |
| Applicable chassis | E81, E82, E87, E88, E90, E91, E92, E93, E60, E83, E84, E85, E86 |
| Badge names | 118i, 120i, 316i, 318i, 320i, 520i, X1 sDrive18i, X3 2.0i, Z4 2.0i |
| Real-world UK MPG | 30 to 38 mpg combined, 38 to 44 mpg motorway |
| Emissions / ULEZ | Euro 6, ULEZ-compliant |
| Successor | N43 (UK direct injection), later N20 and B48 |
| Reliability score | 6 / 10 (Bimmer.AI internal) |
Common problems
Every failure mode below is based on UK DVSA/recall data, BMW press archives, and observed patterns across independent specialist maintenance schedules. Cost ranges are indicative UK figures.
| Failure mode | Severity | Frequency | Typical onset | UK repair range |
|---|---|---|---|---|
| Timing chain guide and tensioner wear | Serious | Common | 80 to 140k mi | £800 to £1,400 |
| Oil consumption from valve stem seals and crankcase breather | Moderate | Very common | 60 to 120k mi | £150 to £1,500 |
| Valvetronic eccentric shaft sensor or motor failure | Moderate | Common | 70 to 130k mi | £300 to £600 |
| VANOS solenoids and seals | Mild | Common | 60 to 120k mi | £100 to £300 |
| Mechanical water pump and thermostat failure | Moderate | Common | 70 to 120k mi | £300 to £500 |
Timing chain guide and tensioner wear
- Rattle for a few seconds on a cold start
- Chain noise from the front of the engine at idle
- Cam and crank correlation fault codes
What to do about it: A new tensioner (£100 to £200) quiets early wear. Full chain, guides and tensioner £800 to £1,400 at a specialist, far less than an N47 because the chain is at the front.
If ignored: Chain jumps, valves meet pistons, £2,500 or more.
UK repair exposure: £800 to £1,400.
Oil consumption from valve stem seals and crankcase breather
- Blue smoke on start-up after sitting, clearing quickly
- Oil use around a litre per 1,000 miles
- Oily spark plugs
- Whistle from the dipstick tube or oil filler when the breather has failed
What to do about it: Replace the crankcase breather (CCV) first, £150 to £300. Stem seals are a head-off job at £900 to £1,500.
If ignored: Fouled plugs, catalyst damage, and in winter a frozen breather can force oil past seals.
UK repair exposure: £150 to £1,500.
Additional notes: Check the oil level and the exhaust tips at viewing. Sooty, oily tips on a petrol car point here.
Valvetronic eccentric shaft sensor or motor failure
- Rough idle and stalling
- Engine warning light with Valvetronic codes
- Reduced power or limp mode
What to do about it: Replace the sensor; it lives under the valve cover so combine with a valve cover gasket.
If ignored: Stalling and limp mode; not engine-damaging.
UK repair exposure: £300 to £600.
VANOS solenoids and seals
- Rough idle
- Flat spot at low revs
- Cam timing fault codes
What to do about it: Clean or replace the solenoids at an oil change.
If ignored: Poor running and economy only.
UK repair exposure: £100 to £300.
Mechanical water pump and thermostat failure
- Coolant weep from the pump weep hole
- Temperature gauge climbing in traffic
- Slow warm-up when the thermostat sticks open
What to do about it: Replace pump and thermostat together around 90,000 miles.
If ignored: Overheating and head gasket failure.
UK repair exposure: £300 to £500.
Preventative maintenance schedule
UK independent specialist consensus, typically more cautious than BMW's factory service intervals, especially around oil and timing components.
| Task | Interval | Typical cost | Fix |
|---|---|---|---|
| Engine oil + filter (BMW LL-01) | Every 7,500 mi | £70 to £120 | DIY |
| Spark plugs (4) | Every 60,000 mi | £80 to £150 | DIY |
| Air filter | Every 30,000 mi | £25 to £45 | DIY |
| Coolant | Every 60,000 mi | £100 to £160 | Specialist |
| Brake fluid | Every 24,000 mi | £60 to £100 | Specialist |
| Crankcase breather (CCV) Cures most oil-consumption complaints | At 80,000 mi | £150 to £300 | Specialist |
| Timing chain tensioner check or replacement | At 90,000 mi | £100 to £200 | Specialist |
Long-term verdict
Adequate rather than brilliant: an economical four that suffers oil consumption and Valvetronic niggles more than outright failures. Timing chain wear is real but the chain is front-mounted and the job costs half an N47's. Blue smoke on a cold start is the tell. ULEZ-compliant petrol keeps 118i, 318i and X1 18i values steady. BMW brought the N46 back into the 316i and 318i in 2010 to 2012 after N43 injector problems, so a late E90 may have either engine.
Buy, negotiate, or walk away
Buy
No blue smoke on cold start, oil level stable between services, crankcase breather and Valvetronic sensor replaced, water pump and thermostat done, no cold-start rattle beyond a second.
Negotiate
Uses a litre of oil every 1,000 miles (breather and stem seals, £150 to £1,500). Cold-start rattle on a car past 100,000 miles with no chain history (£800 to £1,400). Active Valvetronic fault.
Walk away
Heavy blue smoke that persists when warm, a chain rattle that lasts, or a car sold as an N46 that turns out to be an N43 with injector codes.
Check a specific N46 listing
Paste any BMW N46 listing, VIN, or registration. Bimmer.AI returns a N46-specific buyer report in 30 seconds.
Run a Bimmer.AI buyer report →Bimmer.AI is designed to help you identify BMW-specific buyer risks before you travel, negotiate, or pay for an inspection. It does not replace a physical inspection by a qualified mechanic, a legal vehicle-history check (e.g. HPI Check), or independent verification of finance, stolen, or write-off status. Repair-cost ranges are indicative UK figures that vary by region, specialist, parts supply, and labour rates.
Frequently asked questions
Is the BMW N46 engine reliable?
Reasonably. It has no catastrophic failure mode; the issues are oil consumption (valve stem seals and the crankcase breather), Valvetronic eccentric-shaft sensor or motor faults, VANOS solenoids, the mechanical water pump and a front-mounted timing chain that wears past 100,000 miles. Every one is cheaper than the equivalent on an N47 or N43. Bimmer.AI scores it 6 out of 10.
N46 vs N43: which is better?
The N46. Both are 2.0-litre fours in the same cars (E87 1 Series, E90 3 Series), but the N43 is the UK-only direct-injection lean-burn version with piezo injectors that fail at £1,200 to £2,000 a set and a NOx sensor that follows. The N46 uses port injection and has none of that. BMW reverted the 316i and 318i to the N46 in 2010 to 2012 for that reason.
Does the N46 have timing chain problems?
Milder ones than the N47 diesel it is often confused with. The N46 chain and guides wear from around 80,000 to 140,000 miles and produce a cold-start rattle, but the chain is at the front of the engine, so replacement is £800 to £1,400 rather than £1,500 to £2,500. Listen on a cold start and check for cam-crank correlation codes.
Why does my N46 use oil?
Two things: hardened valve stem seals letting oil down the guides (blue smoke on start-up after standing) and a failed crankcase ventilation valve pulling oil into the intake. The breather is £150 to £300 and worth doing first. Stem seals are a £1,000 to £1,500 head-off job, only justified on a car worth keeping.