BMW 318i (E90) engine: which one, problems and replacement

The BMW 318i in the fifth 3 Series saloon generation (E90, built 2005–2012) was built with one engine, the N46B20: a 2.0 L petrol inline-4 with 150 hp.

This guide tells you which engine your 318i has, what goes wrong with it, what a replacement costs from our stock and what else to plan for when you fit one.

• Generation: fifth 3 Series saloon, 2005–2012
• Body styles: E90 (saloon)
• Engines: N46B20
• Output: 150 hp
• Replacement engines in stock: ask the desk for the next arrival

Which engine is in your 318i?

N46B20 in the 318i

The N46B20 was used in the E90 318i, built 2004–2012. It is a 2.0 L naturally aspirated petrol inline-4 with 150 hp and 200 Nm.

Reading the code: N marks an N-series code, the generation of BMW engines introduced from 2001; 46 is the family number; B stands for petrol (from the German Benzin); 20 is the capacity in decilitres, so 2.0 litres.

318i engines by model year

The 318i kept the same engine for the whole E90 run, which makes ordering simple: any unit with the same code fits, subject to the gearbox, drive type and sump.

Other cars with the same engine as the 318i

A replacement engine does not have to come from another 318i. These models left the factory with the same engine code, so a unit from any of them is a candidate donor once the sump, mounts and ancillaries are matched to your car.

N46B20: BMW E87 118i, BMW E60 520i, BMW E84 X1 18i.

How to confirm your engine code

The 318i only used the N46B20, but the exact version can still change with the build date, gearbox and market. Send us the last seven characters of the VIN and we read the engine code from BMW's records, or look for the code stamped on the block. How to find your BMW engine code.

Known 318i engine problems

The N46B20 in the 318i shares the known weak points of the N42 and N46 family. Full N42 and N46 guide.

Oil consumption. Valve stem seals and piston rings let oil through; consumption above one litre per 1,000 km is not unusual on neglected engines.

Timing chain stretch. The N46 chain and tensioner wear, causing rattle and timing faults.

Valvetronic motor and eccentric shaft sensor. Both can fail and leave the engine in limp mode.

Vacuum pump and oil leaks. The vacuum pump seal and the valve cover gasket leak oil.

Crankcase ventilation. The CCV diaphragm splits, causing lean codes and a whistle.

Symptoms to watch for on the 318i

Rattle for a few seconds after a cold start. The classic sign of a weak timing chain tensioner or stretched chain. It must be checked quickly: a chain that jumps a tooth can bend valves.

Poor low-down torque and uneven idle. VANOS seals or solenoids. The engine may run well at high revs but feel flat and lumpy at low speed.

Limp mode with a Valvetronic fault. The Valvetronic motor, its eccentric shaft sensor or the wiring. The engine runs on a reduced throttle until it is repaired.

Looking after the 318i engine

• Oil: 5W-30 BMW Longlife-01 or Longlife-04, about 4.25 litres.
• Service interval: Oil every 15,000 km; shorten to 10,000 km to protect the chain.
• Timing drive: Timing chain at the front with balance shafts.
• Workshop notes: Replace the timing chain, tensioner and valve stem seals when fitting a high-mileage used N46.

Buying a used engine for the 318i: checklist

1. Sump, oil pickup and drive variants. Rear-drive, xDrive and front-drive cars can use different sumps, oil pickups and engine mounts even with the same engine code. Check that the sump matches your subframe and front axle.
2. Why your old engine failed. Before fitting a replacement, find out why the original failed. An overheating radiator, a blocked intercooler or a failed turbo can destroy a second engine if they are not fixed.
3. Compression or leak-down figures. Even compression across all cylinders tells you more than mileage. Ask for the figures, not just a pass or fail, and compare the highest and lowest readings: a spread above 10 to 15 percent deserves a question.
4. Warranty terms in writing. Read what the warranty covers, how long it runs and what fitting conditions apply. Most warranties require a qualified workshop, new fluids and filters, and replacement of the cooling parts that caused the original failure.
5. Look at the oil and coolant. Clean oil without metal particles and coolant without oil are good signs. Milky oil, oily coolant or a burnt smell mean the engine needs further checks before it is fitted.
6. Timing chain noise. Listen for a rattle at the front of the engine for the first seconds after a cold start. On an engine that cannot be run, look at the chain guides through the oil filler or with the valve cover off.
7. VANOS operation. Rough idle, a rattle from the front of the head and a loss of torque at low revs point to VANOS seals or solenoids. These are serviceable parts and are easier to renew with the engine out.
8. Double VANOS units and solenoids. Ask for the adaptation values or fault history if the engine was running. Solenoids are inexpensive and are often replaced as a matter of course on a used engine.
9. Valvetronic motor and eccentric shaft sensor. The Valvetronic motor and its sensor cause limp-mode faults when they fail. Inspect the connector and the seal around the motor for oil.

BMW 318i replacement engine cost

We do not have a 318i engine on the shelf at the moment. Send us your VIN or the code you need and the desk will tell you when the next unit arrives and what it will cost.

On top of the engine, budget for the workshop's labour and the parts that are best replaced while the engine is out: engine mounts, the rear main seal, cooling parts, a clutch or converter seal, fluids and filters.

Will it fit my 318i?

Will the N46B20 fit my BMW E90 318i?

Yes, the BMW E90 318i left the factory with the N46B20, so an N46B20 from another car is the direct replacement. The fifth 3 Series saloon was built 2005–2012, and the N46B20 was produced 2004–2012, so check that your car's build date falls inside that window. Confirm the drive type (rear-drive or xDrive), the gearbox (manual or automatic) and the emissions standard, because these can change the sump, the flywheel and the software. Send us the VIN and we check all of it for you.

How much is a replacement engine for a BMW E90 318i?

We do not have an N46B20 on the shelf for the E90 318i at the moment. Units arrive regularly; send us your VIN and we will tell you when the next one is ready and what it will cost, including delivery.

Engine swaps and upgrades for the 318i

These engines were fitted to other versions of the E90 at the factory, which makes them the most practical upgrades: the body was designed around them and many parts are shared.

Can I fit the N43B20 in my 318i?

Yes, it is one of the more common upgrades. Both are petrol inline-4 engines, so the mounting points are similar, but the N43B20 needs its own wiring and engine control unit, the matching gearbox or clutch, and often a different sump, cooling and exhaust. The gain is 20 hp and 10 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Can I fit the N45B20S in my 318i?

Yes, it is one of the more common upgrades. Both are petrol inline-4 engines, so the mounting points are similar, but the N45B20S needs its own wiring and engine control unit, the matching gearbox or clutch, and often a different sump, cooling and exhaust. The gain is 23 hp and 0 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Can I fit the N47D20 in my 318i?

It is a full conversion: the N47D20 runs on diesel and the N46B20 on petrol, so the fuel system, wiring, engine control unit, instrument coding and usually the gearbox change too. The gain is 34 hp and 180 Nm. In Germany and most of Europe an engine swap must be inspected and registered.

Fitting a replacement engine in the 318i

1. Inspect or replace the timing chain parts. Look at the guides and tensioner. On high-mileage engines, replacing them now costs far less than doing it later.
2. Reset VANOS adaptations. Clear the VANOS adaptations so the ECU learns the camshaft positions of the new engine.
3. Teach the Valvetronic limit stops. Run the Valvetronic learning routine so the ECU knows the eccentric shaft limits.
4. Fill with the right oil and prime it. Fill with new oil of the correct specification and a new filter. Crank with the fuel and ignition disabled until oil pressure builds.
5. Coding and adaptations. On modern BMWs, the engine ECU must be matched to the car's immobiliser (CAS, FEM or BDC). Reset adaptations, register the battery and clear faults with diagnostic software.
6. First start and leak check. Start the engine, let it idle and watch oil pressure, temperature and fault codes. Check for leaks and bleed the cooling system.
7. First 1,000 km. Drive gently for the first few hundred kilometres, vary the engine speed and avoid full load. Change the oil and filter after about 1,000 km to remove any assembly debris.

The full fitting and first-start procedure.

318i engine questions

What should I replace when I fit a used N46B20 engine?

A used engine lasts longest when it starts life in your car with fresh fluids and new seals. Fit a new oil filter and fresh oil of the grade BMW lists for this engine, and refill the coolant with the correct BMW antifreeze mix. Change the drive belt, the thermostat and the water pump seals if they look tired, because they are cheap while the engine is out. Use new gaskets for the exhaust manifold, the intake and the sump plug, and check every hose clip before the first start.

Look at the engine mounts and the clutch or the torque converter while the engine is out. Old mounts can crack a new engine's brackets, and a worn clutch is much easier to change now.

Before the first start, turn the engine over without fuel until the oil pressure light goes out. Then let it idle, check for leaks, and drive gently for the first few hundred kilometres.

The warranty asks for fitting by a qualified mechanic and the correct oil, coolant and filters. Keep your receipts in case you ever need to make a claim.

See all N46 Engines · Search N46B20 in the shop

How do I know a used N46B20 engine is in good shape?

Each engine in the yard is inspected in Hamburg. The code is matched to the listing, the parts on the engine are recorded, the openings are sealed and the real unit is photographed. An inspection certificate for the unit can travel with the order when you ask for it.

When you look at a listing, check the recorded mileage, the year and the photos of the ports and the stamp. Ask for photos of anything you want to see closer. If you want more photos or a short video of a unit, ask the desk and we send them before you pay.

On a petrol engine like the N46B20, a careful fitter will also look at the spark plugs, the coils and the timing side before the engine goes in.

If the engine fails inside under normal use, the warranty covers you. Eligible engines come with a 12 months warranty from the delivery date. It covers internal mechanical failure under normal use and correct fitting by a qualified mechanic or workshop.

See all N46 Engines · Search N46B20 in the shop

What is the BMW N46B20 engine?

The BMW N46B20 is a 2.0 liter (1,995 cc) petrol engine from the N46 family. It has an inline 4, DOHC, 16 valve layout with no turbo (naturally aspirated), and makes 110 kW (150 HP) with 200 Nm of torque. BMW built it from 2004 to 2012 and it meets the Euro 4 emission standard.

You find the N46B20 in the BMW E90 320i, BMW E87 120i, BMW E60 520i and BMW E46 318i. What we list: BMW N46 1.6 and 2.0 petrol engines for 316i and 320i.

At Autowerke Engines every N46B20 is a real used engine from our yard in Hamburg. Before a unit is listed, the yard checks the engine code against the listing, writes down the parts fitted to it, seals every opening and photographs the real engine you will receive. Each listing shows the year, the mileage and the price, so you can compare units side by side.

Not sure? Send us your VIN and your gearbox code. We match the engine family, the year window and the parts on the engine before anything is reserved, and the check is free.

See all N46 Engines · Search N46B20 in the shop

Which cars use the BMW N46B20 engine?

BMW fitted the N46B20 to the BMW E90 320i, BMW E87 120i, BMW E60 520i and BMW E46 318i. These cars were built with this engine from about 2004 to 2012.

The badge on the boot is not enough to be sure. The same model name can hide two different engines, for example after a facelift or a change in emission rules. Always read the engine code stamped on the block, or look it up with your VIN.

The N46B20 is the only N46 version we list, which makes it easy to pick, but the wiring and the engine computer still need to match your car.

Not sure? Send us your VIN and your gearbox code. We match the engine family, the year window and the parts on the engine before anything is reserved, and the check is free.

See all N46 Engines · Search N46B20 in the shop

Delivery, warranty and payment

Before a 318i engine leaves our Hamburg yard it is drained of oil and coolant, every opening is sealed, and it is strapped to a pallet and wrapped. We send photographs of the packed unit and the tracking details.

Door-to-door delivery is included to the address you give at checkout. Typical delivery takes three to five working days within Germany and neighbouring countries and five to ten working days to the rest of Europe and the UK.

A 12-month warranty covers eligible internal failure when the engine is fitted by a qualified workshop with new fluids and filters. You can pay by card, bank transfer or crypto and receive the invoice by email straight away.

All E90 engines · N42 and N46 engine guide · BMW 318i engines for sale · Send us your VIN