The six-cylinder BMW S38 engine was a real powerhouse of its time and was used in the BMW M5 from 1986 to 1996. The S38 is quite a unique engine compared to what you will find in BMW engines from the time and nowadays, and it was quite a beast for an inline six at the time, reaching 340 horsepower.
The BMW S38 was an extremely unique engine for its time and it was more complex and powerful than its inline-six peer, the S52. Given the added complexity, the S38 did come with some additional problems such as valve design problems stemming from a lack of hydraulicly-adjusted valves, timing component failure stemming from a flaw in the tensioner design and preemature coolant system failure.
Read on to learn about what truly makes the S38 unique and some of the most common engine problems that an owner will typically experience with one.
The BMW S38 Was A Developmental Leap From the M30
BMW used the S38 engine in the BMW M5 between the years 1986 to 1996 and it replaced the M88 engine. The S38 shares a lot of similarities with the M88, however, the S38 features a dual overhead camshaft, six individual throttle bodies and a 24-valve cylinder head. This gave the engine some added power, which as you will see in the below table, reached 340 horsepower in 1992.
The displacement and output of the S38 was increased twice during the engine’s lifetime.
| Year | Displacement | Power | Torque |
| 1986 | 3453cc | 252hp | 330Nm @ 4,500rpm |
| 1989 | 3535cc | 315hp | 360Nm @ 4,750rpm |
| 1992-1996 | 3795cc | 340hp | 400Nm @ 4,750rpm |
The BMW S38 Engine Does Have Some Faults
The Guide Rails
Preventative maintenance when it comes to this engine’s timing components is a must at this point as these vehicles are well over 20 years old. You should be inspecting the timing components (guide rail, timing chain, tensioner) periodically as you don’t want these components to fail.
The S38 engine has an overall strong reputation, evidenced y the fact that many owners today are driving around S38’s with well over 150,000 miles. However, you should be aware that the most common chink in the armor on these vehicles is that the guide rails and timing tensioner can and likely will fail prematurely.
The general consensus among owners is to have these components replaced around the 70,000-80,000 mile range. There are several alternative guide rails and tensioners available on the market that will provide enhanced reliability.
The Valve Design
One thing that BMW could have done away with when it moved from the M88 to the S38 was the shim and bucket style valvetrain. Unfortunately, BMW did not and that means instead of working with hydraulically-adjusted valves, your S38 engine has metal shims that require relatively frequent inspection and adjustment.
The good news here is that valve shim adjustment is relatively easy to do for any DIYer. You can find a good write up on the procedure here. Something to note is that for this job it is absolutely critical that you have (i) the valve adjustment tool (BMW part # 113-170) and (ii) a set of angled feeler gauges.
Coolant System Failure
Frequent readers might tire at some point of me constantly reiterating that the coolant system design on BMWs is notoriously weak, however, this statement remains true with the S38 so I will mention it here.
The coolant system comes with some of the same issues that BMW owners will be well aware of. Water pump issues, plastic radiator components and hoses crack and break, and when they do all hell can break lose.
Therefore, it is extremely important to practice preventative maintenance and replace your entire cooling system every 80,000 miles or so. Too many BMWs have been sent to the junkyard due to premature coolant system failure, which causes the engine to quickly overheat. Don’t let your S38 become one of those engines.
Oil Leaks
Another common issue on the S38s once they rack up some decent mileage is oil leaks. A few common problem areas are listed below:
- front timing case cover (upper and lower)
- front crank seal
- oil pan gasket
- rear main seal
- oil return tube at lower right rear of engine block
- valve cover gasket
Keep in mind though that an engine does not have to be 100% leak free to operate well. In fact, I can’t remember a time when my old E36s or E46s were not losing at least a little bit of oil between changes. At this point in your S38’s life, it will be incredibly difficult to keep the vehicle “leak free”. The best most of us can hope for is to limit oil leaks to a minor inconvenience and fix ones that cause significant amounts of oil loss.
That being said, timing case covers and valve cover gaskets are incredibly quick and simple to fix. Oil pan gaskets and rear main seals, on the otherhand, will require a significant amount of hours to replace.
Conclusion
The BMW S38 was a big step-up from the M88. The engine produces more power and was built with a few updates in mind. Unfortunately, we would have to wait a little bit longer for BMW to introduce hydraulic lifters into this line of vehicles and the common timing component failure is a major fault.
My recommendation is that if you are considering purchasing an E34 M5, make sure that the previous owner has the paperwork indicating that the various problematic timing components have been replaced. This can be an expensive and time consuming repair so it’s best that it has previously been handled or at the very least the vehicle is discounted.