BMW N45 Engine Reliability Guide
The BMW N45 is the 1.6-litre four-cylinder petrol without Valvetronic in the E87 116i of 2004 to 2007, and, as the special 2.0-litre N45B20S, the engine in the E90 320si homologation saloon. Two very different reputations under one code: dependable and slow in the 116i, fragile and collectible in the 320si.
Quick verdict
Establish which N45 you are looking at before anything else. In the 116i it is a simple engine whose worst habits are oil consumption and a rattly chain tensioner. In the 320si the N45B20S block cracks between the cylinders, and a car without proof of a replacement block is a £4,000 to £7,000 gamble. ULEZ-compliant in both cases.
What is the BMW N45?
116i N45 cars are the cheapest E87s in the country, £1,000 to £3,000 with high mileage and thin history, sold to first-time buyers. The 320si is the opposite: 2,600 built for touring-car homologation, now an enthusiast car at £5,000 to £12,000 where block history is the entire conversation. BMW replaced many 320si blocks under warranty; the invoice is worth more than the paint.
| Full engine code | N45B16 |
|---|---|
| Configuration | I4 naturally aspirated petrol, no Valvetronic (N46 sibling); 2.0 N45B20S in the 320si |
| Production years | 2004-2011 |
| Applicable chassis | E81, E87, E90 |
| Badge names | 116i, 320si |
| Real-world UK MPG | 34 to 42 mpg combined, 42 to 48 mpg motorway |
| Emissions / ULEZ | Euro 6, ULEZ-compliant |
| Successor | N43 (116i from 2007), later N13 |
| 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 |
|---|---|---|---|---|
| Cylinder block and liner cracking (320si N45B20S only) | Catastrophic | Common | 40 to 100k mi | £4,000 to £7,000 |
| Timing chain tensioner rattle | Moderate | Common | 80 to 140k mi | £600 to £1,200 |
| Oil consumption and crankcase breather failure | Moderate | Common | 60 to 120k mi | £150 to £1,200 |
| Ignition coil and spark plug misfires | Mild | Common | 50 to 100k mi | £100 to £300 |
| Water pump and thermostat failure | Moderate | Common | 70 to 120k mi | £300 to £500 |
Cylinder block and liner cracking (320si N45B20S only)
- Coolant loss with no visible leak
- Overheating
- White exhaust smoke and a misfire
- Oil and coolant mixing (mayonnaise under the filler cap)
What to do about it: None. Check the history for a replacement block or engine under BMW's goodwill scheme and get a compression and coolant pressure test before buying.
If ignored: Engine write-off.
UK repair exposure: £4,000 to £7,000.
Recall / TSB: BMW UK replaced many 320si blocks under goodwill in the late 2000s. The programme has ended.
Additional notes: Applies only to the 2,600-off 320si homologation special, not the 116i. Homologation cars with a documented replacement block are the ones to buy.
Timing chain tensioner rattle
- Rattle on cold start
- Chain noise at idle from the front of the engine
What to do about it: New tensioner at first noise; full chain kit if the guides are worn.
If ignored: Chain jump and valve damage.
UK repair exposure: £600 to £1,200.
Oil consumption and crankcase breather failure
- Blue smoke on start-up
- Oil use around a litre per 1,000 miles
- Whistle from the oil filler with the cap loosened
What to do about it: Replace the crankcase breather first; stem seals only if smoke persists.
If ignored: Fouled plugs and catalyst damage.
UK repair exposure: £150 to £1,200.
Ignition coil and spark plug misfires
- Misfire codes
- Stutter under load
What to do about it: Plugs on schedule; coils as they fail.
If ignored: Catalyst damage.
UK repair exposure: £100 to £300.
Water pump and thermostat failure
- Coolant weep from the pump
- Gauge climbing in traffic
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) | At 80,000 mi | £150 to £300 | Specialist |
Long-term verdict
In the 116i the N45 is a simple, slow and largely dependable 1.6 whose worst habits are oil consumption and a rattly chain tensioner. In the 320si it is a different engine: the special N45B20S block cracks, and a car without proof of a replacement block is a gamble. Establish which one you are looking at before anything else. ULEZ-compliant.
Buy, negotiate, or walk away
Buy
116i: oil level stable, no lasting cold-start rattle, water pump and breather done. 320si: documented replacement block or a specialist pressure test and coolant analysis, plus a stable coolant level.
Negotiate
116i with a chain tensioner rattle (£600 to £1,200) or oil use. 320si with original block and no test evidence: the price must carry the risk.
Walk away
320si with coolant loss, mayonnaise under the oil cap or a seller who cannot answer the block question. 116i with a rattle that lasts and no history.
Check a specific N45 listing
Paste any BMW N45 listing, VIN, or registration. Bimmer.AI returns a N45-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 116i N45 engine reliable?
Broadly yes. The 1.6 N45 in the 2004 to 2007 116i is slow but simple: the known items are a timing chain tensioner rattle past 80,000 miles (£600 to £1,200), oil consumption from the crankcase breather (£150 to £300), coils and plugs, and the water pump and thermostat. It was replaced by the direct-injection N43 in 2007, which is worse.
What is wrong with the BMW 320si engine?
The N45B20S in the E90 320si was a homologation special with a thin-wall aluminium block and open-deck liners that crack between the cylinders, typically at 40,000 to 100,000 miles. Coolant loss, white smoke and mayonnaise under the oil cap are the signs; the fix is a replacement block at £4,000 to £7,000. BMW replaced many under warranty, so the invoice trail is the whole buying decision.
How many BMW 320si were made?
Around 2,600 worldwide, built in 2006 to 2007 to homologate the E90 for the World Touring Car Championship. UK cars are right-hand drive and were sold new for around £23,000. Good examples with a documented block are gently appreciating; unknown ones are not.
Is the N45 ULEZ-compliant?
Yes, both the 1.6 116i and the 2.0 320si are Euro 4 petrol and inside the ULEZ standard.