The BMW 325i in the second 3 Series generation (E30, built 1982–1994) was built with one engine, the M20B25: a 2.5 L petrol inline-6 with 170 hp.
Below you will find how to identify the engine in your 325i, the faults to look for, current prices for a replacement and the swap options that make sense.
- Generation: second 3 Series, 1982–1994
- Body styles: E30 (saloon, Touring, coupé, convertible)
- Engines: M20B25
- Output: 170 hp
- Replacement engines in stock: ask the desk for the next arrival
Which engine is in your 325i?
| Engine code | Built | Power | Torque | Type |
|---|---|---|---|---|
| M20B25 | 1985–1993 | 170 hp | 226 Nm | 2.5 L petrol inline-6, naturally aspirated |
M20B25 in the 325i
The M20B25 was used in the E30 325i, built 1985–1993. It is a 2.5 L naturally aspirated petrol inline-6 with 170 hp and 226 Nm.
Reading the code: M marks an M-series code, the naming BMW used for its engine families up to the early 2000s; 20 is the family number; B stands for petrol (from the German Benzin); 25 is the capacity in decilitres, so 2.5 litres.
325i engines by model year
| Model year | Engine |
|---|---|
| 1985 | M20B25 (170 hp) |
| 1986 | M20B25 (170 hp) |
| 1987 | M20B25 (170 hp) |
| 1988 | M20B25 (170 hp) |
| 1989 | M20B25 (170 hp) |
| 1990 | M20B25 (170 hp) |
| 1991 | M20B25 (170 hp) |
| 1992 | M20B25 (170 hp) |
| 1993 | M20B25 (170 hp) |
The 325i kept the same engine for the whole E30 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 325i
A replacement engine does not have to come from another 325i. 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.
M20B25: BMW E34 525i, BMW Z1.
How to confirm your engine code
The 325i only used the M20B25, 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 325i engine problems
The M20B25 in the 325i shares the known weak points of the M20 family. Full M20 guide.
| Known fault | What to check |
|---|---|
| Timing belt failure | Ask for the date of the last belt and tensioner change. If there is no record, treat it as due. |
| Cylinder head cracks | Pressure-test the cooling system and look for cracks when the cam cover is off. |
| Rocker arm and shaft wear | Inspect rockers and clips with the cam cover removed. |
| Oil spray bar and cam wear | Check the spray bar banjo bolts are tight and the holes clear. |
| Water pump and thermostat | Look for coolant trails below the pump and on the belt cover. |
Timing belt failure. The M20 is an interference engine. If the belt or tensioner fails, pistons hit valves and the head is scrap. Belts should be changed every 60,000 km or four years, whichever comes first.
Cylinder head cracks. Heads crack between the camshaft journals or between valve seats after overheating. Coolant loss and a sweet smell are the clues.
Rocker arm and shaft wear. Rocker arms can crack and the retaining clips can walk off the shaft. The 'rocker arm fix' with improved clips is a known upgrade.
Oil spray bar and cam wear. A loose or blocked spray bar starves the cam lobes. The result is a worn cam and noisy valve train.
Water pump and thermostat. The water pump is driven by the timing belt and is normally changed with it. A weeping pump can soak the new belt.
Symptoms to watch for on the 325i
Engine stops suddenly and will not restart. On belt-driven engines, a snapped timing belt. Do not keep cranking: on an interference engine the valves are probably already bent.
Looking after the 325i engine
- Oil: 10W-40 or 15W-40 semi-synthetic, about 4.25 litres with filter.
- Service interval: Oil every 7,500 km; valve clearances every 15,000 km; belt on time, not only on distance.
- Timing drive: Rubber timing belt with tensioner, changed with the water pump every 60,000 km or four years.
- Workshop notes: Valve clearance is set cold at about 0.25 mm with eccentric adjusters. Use a new head bolt set whenever the head comes off.
Buying a used engine for the 325i: checklist
- 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.
- 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.
- 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.
- List of what is fitted. Engines are sold with different ancillaries: some have the turbo, injectors, manifolds, alternator and starter, others are long blocks. Agree the list in writing so you know which parts must come from your old engine.
- Ask how the donor car was damaged. Most good used engines come from cars with body damage. A front-end impact can crack sensors, the timing cover or the sump; a rear or side impact usually leaves the engine untouched. The yard records the damage on each unit.
- Timing belt history. A timing belt must be changed on time and distance. With no dated record, treat the belt, tensioner and water pump as due and replace them before the first start.
- Originality and numbers. For collectible cars, the engine number and correct ancillaries add value. Photograph the stamp and keep it with the car's documents.
BMW 325i replacement engine cost
We do not have a 325i 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 325i?
Engine swaps and upgrades for the 325i
These engines were fitted to other versions of the E30 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 S14B20 in my 325i?
It is a conversion rather than a replacement: the S14B20 is an inline-4 and your M20B25 an inline-6, so mounts, sump, cooling, exhaust, wiring and the engine control unit all change. The gain is 22 hp and 0 Nm. In Germany and most of Europe an engine swap must be inspected and registered.
Can I fit the S14B23 in my 325i?
It is a conversion rather than a replacement: the S14B23 is an inline-4 and your M20B25 an inline-6, so mounts, sump, cooling, exhaust, wiring and the engine control unit all change. The gain is 30 hp and 14 Nm. In Germany and most of Europe an engine swap must be inspected and registered.
Fitting a replacement engine in the 325i
- Fit a new timing belt kit. Fit a new belt, tensioner and water pump and set the timing with the correct tools before the first start.
- 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.
- 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.
- 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.
- 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.
325i engine questions
How much is a replacement M20B25 engine for a BMW E30 325i?
A used M20B25 for the BMW E30 325i costs from about 1.300 € to 2.200 € in our yard. The price depends on the year, the mileage and the parts that come with the engine.
Shipping is a flat 249 € per order. It is added once at checkout and printed on the invoice, so there is no extra fee later. Inside the EU there is no import duty. Outside the EU, the receiver pays local duty and VAT.
A replacement engine is often much cheaper than rebuilding a damaged one, and much faster. The M20B25 you buy is photographed and checked in Hamburg before it is listed.
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. 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 M20 Engines · Search M20B25 in the shop
Will the M20B25 engine fit my BMW E34 525i?
Yes, if your BMW E34 525i was built with the M20B25. BMW used this 2.5 liter (2,494 cc) petrol engine with 126 kW (171 HP) in the E34 525i from about 1985 to 1993.
Some E34 525i cars were built with a different engine: the M50B25. These look alike from the outside, so check the code on your engine or send us your VIN.
Also tell us if your E34 has a manual or an automatic gearbox. The flywheel or the flex plate and some sensors depend on it.
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 M20 Engines · Search M20B25 in the shop
How much power and torque does the BMW M20B25 have?
From the factory the BMW M20B25 makes 126 kW (171 HP) and 226 Nm of torque. It is a 2.5 liter (2,494 cc) inline 6, SOHC, 12 valve petrol engine with no turbo (naturally aspirated).
Without a turbo, the power builds smoothly with the revs. A clean air intake, healthy ignition and the correct fuel are key to getting the full figure.
A used engine reaches its factory numbers when it is fitted with the matching engine computer and software, and serviced with the right oil and filters. If the engine computer from your car is a different version, a specialist may need to code it.
Every M20B25 on our site lists its year and mileage. Ask the desk for more pictures of any listing. We are happy to show the stamp, the ports and the ancillaries before you decide.
See all M20 Engines · Search M20B25 in the shop
How much is a replacement M20B25 engine for a BMW E30 325is?
A used M20B25 for the BMW E30 325is costs from about 1.300 € to 2.200 € in our yard. The price depends on the year, the mileage and the parts that come with the engine.
Shipping is a flat 249 € per order. It is added once at checkout and printed on the invoice, so there is no extra fee later. Inside the EU there is no import duty. Outside the EU, the receiver pays local duty and VAT.
A replacement engine is often much cheaper than rebuilding a damaged one, and much faster. The M20B25 you buy is photographed and checked in Hamburg before it is listed.
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. 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 M20 Engines · Search M20B25 in the shop
What is the difference between the M20B25 and other M20 engines?
The M20B25 makes 126 kW (171 HP) and 226 Nm. The other M20 engines are: M20B20 with 95 kW (129 HP) and 174 Nm (1977 to 1992).
Engines in one family share a basic block, but the turbo, the injection, the sensors and the engine computer can differ. A higher power version often has different pistons, a bigger turbo or a different fuel system.
This is why we ask for the exact code. Fitting a different version can work, but the wiring, the software and sometimes the gearbox must be changed to match.
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 M20 Engines · Search M20B25 in the shop
Will the M20B25 engine fit my BMW Z1?
Yes, if your BMW Z1 was built with the M20B25. BMW used this 2.5 liter (2,494 cc) petrol engine with 126 kW (171 HP) in the Z1 from about 1985 to 1993.
In our records the M20B25 is the engine for the Z1, which makes the match simple. Still, check the code on your old engine or send us your VIN.
Also tell us if your Z1 has a manual or an automatic gearbox. The flywheel or the flex plate and some sensors depend on it.
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 M20 Engines · Search M20B25 in the shop
How much is a replacement M20B25 engine for a BMW E34 525i?
A used M20B25 for the BMW E34 525i costs from about 1.300 € to 2.200 € in our yard. The price depends on the year, the mileage and the parts that come with the engine.
Shipping is a flat 249 € per order. It is added once at checkout and printed on the invoice, so there is no extra fee later. Inside the EU there is no import duty. Outside the EU, the receiver pays local duty and VAT.
A replacement engine is often much cheaper than rebuilding a damaged one, and much faster. The M20B25 you buy is photographed and checked in Hamburg before it is listed.
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. 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 M20 Engines · Search M20B25 in the shop
How much is a replacement M20B25 engine for a BMW E30 325i?
A used M20B25 for the BMW E30 325i costs from about 1.300 € to 2.200 € in our yard. The price depends on the year, the mileage and the parts that come with the engine.
Shipping is a flat 249 € per order. It is added once at checkout and printed on the invoice, so there is no extra fee later. Inside the EU there is no import duty. Outside the EU, the receiver pays local duty and VAT.
A replacement engine is often much cheaper than rebuilding a damaged one, and much faster. The M20B25 you buy is photographed and checked in Hamburg before it is listed.
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. 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 M20 Engines · Search M20B25 in the shop
Will the M20B25 engine fit my BMW E28 525i?
Yes, if your BMW E28 525i was built with the M20B25. BMW used this 2.5 liter (2,494 cc) petrol engine with 126 kW (171 HP) in the E28 525i from about 1985 to 1993.
In our records the M20B25 is the engine for the E28 525i, which makes the match simple. Still, check the code on your old engine or send us your VIN.
Also tell us if your E28 has a manual or an automatic gearbox. The flywheel or the flex plate and some sensors depend on it.
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 M20 Engines · Search M20B25 in the shop
Delivery, warranty and payment
Before a 325i 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 E30 engines · M20 engine guide · BMW 325i engines for sale · Send us your VIN
