BMW S38 engine explained: the straight-six of the E28 and E34 M5
The BMW S38 powered the first two generations of the M5. Its link with the M1 engine, the 3.5, 3.6 and 3.8-litre versions, maintenance needs and what to check on a classic M5.
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The BMW S38 is the straight-six that powered the first two generations of the M5. Derived from the M88 engine of the M1 supercar, it brought racing technology to a four-door saloon in the 1980s and early 1990s.
With individual throttle bodies, four valves per cylinder and a willingness to rev, the S38 made the E28 and E34 M5 legends. In this article we explain where the S38 comes from, its versions, how it is built, the maintenance it needs and what to check when buying a classic M5.
From the M1 to the M5
The M1 supercar used the M88, a 3.5-litre straight-six with twin overhead camshafts and four valves per cylinder. Our article on the BMW M1 history tells that story.
BMW Motorsport adapted this engine for road cars. In Europe, the M88/3 version powered the M635CSi and the first M5. For markets with stricter emissions rules, and later for all markets, the engine was developed into the S38. The S38 became the heart of the M5 for two generations.
BMW S38 versions
The S38 was produced in several versions:
- S38B35: a 3.5-litre version used in the E28 M5 and E24 M6 for certain markets, with a catalytic converter.
- S38B36: a 3.6-litre version used in the early E34 M5, with around 315 hp.
- S38B38: a 3.8-litre version used in the later E34 M5, with around 340 hp, including the M5 Touring.
The 3.8-litre engine received further improvements to the intake and engine management, and later cars also received other updates to the drivetrain. Our article on BMW M5 generations explains the cars that used these engines.
How the S38 is built
Key features of the BMW S38 include:
- A straight-six with a cast iron block and aluminium cylinder head.
- Twin overhead camshafts driven by a timing chain.
- Four valves per cylinder.
- Individual throttle bodies, one for each cylinder.
- A Motronic engine management system of its era.
- A high rev limit for a road engine of its time.
The S38 is known for its sharp response, strong top-end power and a distinctive mechanical sound.
Maintenance needs
The S38 is a robust engine, but it needs specialist care:
- Valve clearance adjustment at regular intervals, which is important for smooth running and long life.
- Oil changes with suitable oil for a classic high-performance engine.
- Timing chain and tensioner checks, especially on high-mileage engines. Our article on BMW timing chain problems explains warning signs.
- Cooling system maintenance, because overheating can damage the cylinder head.
- Throttle body synchronisation for a smooth idle.
- Ignition and sensors, which age with time.
Parts availability is generally good through BMW Classic and specialists, but some components are expensive.
Common issues
Points to check on an S38 include:
- Oil leaks from the valve cover, timing cover and oil pan. Our article on BMW oil leaks lists common leak points.
- Rough running, which can come from throttle body synchronisation, sensors or vacuum leaks. Our article on BMW rough idle explains the causes.
- Overheating history, which can affect the head gasket and cylinder head.
- Noises from the valvetrain if valve clearance has not been adjusted.
- Exhaust manifold leaks.
A compression test and a careful inspection by a specialist are strongly recommended before buying.
Driving an S38-powered M5
The S38 rewards drivers who use the rev range. It pulls well from low speeds but comes alive at higher revs, with a hard-edged sound from the intake. In the E34 M5, it combines with a well-balanced chassis to create a refined and fast saloon.
Many owners say that the S38 gives the early M5s their character: a mix of motorsport heritage and everyday usability.
Buying a classic M5 with an S38
When buying an E28 or E34 M5:
- Check the service history, especially valve adjustments, timing chain work and cooling system repairs.
- Inspect the body for rust. Our article on BMW rust explains where older BMWs rust.
- Check the originality of the car and engine with the VIN and documents.
- Arrange an inspection with a classic BMW specialist.
Our complete checklist for buying a used BMW M car covers the general steps.
Why the S38 matters
The S38 connected the M1 supercar with the everyday M cars that followed. It showed that a racing-derived engine could power a comfortable four-door car, and it laid the foundation for the M5 as a performance icon.
Today, S38-powered M5s are increasingly valued classics. A healthy S38 with documented maintenance is a joy to own and drive.
BMW S38 engine at a glance
| Item | Details |
|---|---|
| Origin | Derived from the M88 of the M1 |
| Layout | Straight-six, twin cam, four valves per cylinder |
| Versions | 3.5, 3.6 and 3.8 litres |
| E34 M5 3.6 | Around 315 hp |
| E34 M5 3.8 | Around 340 hp |
| Throttle | Individual throttle bodies |
| Key maintenance | Valve clearance, timing chain, cooling |
Frequently asked questions
Which cars have the BMW S38 engine?
The E28 M5 in some markets, the E24 M6 for some markets and the E34 M5, including the M5 Touring.
Is the BMW S38 related to the M1 engine?
Yes. It was developed from the M88 straight-six of the M1 supercar.
Is the S38 reliable?
It is robust when maintained by specialists, with regular valve adjustments and cooling system care.
How much power does the E34 M5 have?
Around 315 hp with the 3.6-litre engine and around 340 hp with the 3.8-litre engine.
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