A couple of weeks ago, we put together a comprehensive piece on the BMW S52 engine. The S52 engine powered the second generation of the BMW M3 — the E36 M3 — in the United States market and enabled the sports coupe to become a rather popular and sought-after machine. Even today, several American enthusiasts own, drive, and relish the simplistic yet potent package that is the E36 M3.
However, the undeniable truth is that E36 M3 owners across the pond had a lot more to enjoy and that we were devoid of what the second-gen M3 was truly capable of. Why? In most overseas markets, BMW equipped the M3 with the S50 engine, a notably more capable unit than the S52 we had access to.
As a result, the E36 M3 was commonly differentiated as either being Euro-spec (with the S50 engine) or U.S.-spec (with the S52 engine). While there are a few examples of the former that were imported onto our shores by individuals, they’re incredibly rare to come by. Nevertheless, the S50 engine is one worth knowing about, even if we might not have the opportunity to experience it.
BMW S50 Engine — A Step up from the S14 Engine
The S50 engine aboard the E36 M3 was the successor to the S14 engine that powered the iconic E30 M3. While the S14 was an inline-four engine, the S50 introduced two additional cylinders, making it the model that set the trend for the M3 cars that followed (most generations of the M3 are powered by an inline-six engine).
Based on the standard M50 engine, the S50 shared much of its construction, albeit with some significant updates. Unfortunately, the S50 did not comply with American emission regulations at the time of its release, so BMW North America was forced to introduce an engine that could. Therein lies the birth of the S52 engine.
During its near-decade-long production run, from 1992 to 2000, the S50 engine saw two iterations — the S50B30 and the S50B32.
S50B30
The S50B30 was the original version of the S50 engine and was in production from 1992 to 1995. It made its way onto nearly every E36 M3 sold outside the United States market. Interestingly, BMW Canada officially imported 45 units of this engine in the first year, but the next batch of cars came with the S52 engine.
With a bore of 86 mm and a stroke of 85.8 mm, the S50B30 displaced 2,990 ccs. And with a compression ratio of 10.8:1, peak output figures were rated at 282 hp at 7,000 rpm and 235 lb-ft of torque at 3,500 rpm.
This engine version featured single-VANOS (variable valve timing on the intake camshaft), individual throttle bodies for each cylinder, and a Bosch Motronic M3.3 engine management system. Compared to the M50 engine it was based on, it also came with redesigned intake and exhaust systems.
S50B32
The S50B32 replaced the S50B30 in 1995 and remained in production until the turn of the millennium. Some notable updates it brought include the addition of double-VANOS (variable valve timing on the intake and exhaust camshafts) and a secondary oil pickup pipe to assist the fuel pump.
The bore and stroke were increased to 86.4 mm and 91 mm, respectively, bumping up displacement to 3,201 ccs. This was the largest and most powerful iteration of the S50 engine, producing 321 hp at 7,400 rpm and 258 lb-ft of torque at 3,250 rpm.
In comparison, the M50B25TU, the most potent version of the standard M50 engine, displaced 2,494 ccs and produced a humble 189 hp and 184 lb-ft of torque.
S50B30US — An America-spec S50 Engine
While the aforementioned engines never officially made it to the United States market, one unique variation bearing the ‘S50’ name did. Used solely on the 1994 and 1995 E36 M3, the S50B30US was largely similar to the standard M50B25TU and shared little in common with its European namesakes.
The S50B30US displaced 2,990 ccs and featured a different crankshaft, connecting rods, camshaft, and pistons.
What’s the Difference between S50 and S52?
Simply put, the S50 engine is a high-performance engine based on the BMW M50 engine, while the S52 sold in the U.S. market finds its roots in the standard M52 engine. The S50 is undeniably the more technologically advanced and capable of the two. It features an iron block with aluminum cylinder heads. In its final form, it came with all that the Bavarians had to offer at the time, like double-VANOS and individual throttle bodies.
Meanwhile, the S52 featured a comparatively rudimentary two-stage VANOS system with just one throttle body for all six cylinders. The S50 also revved more freely through the rev range — 7,600 rpm vs. 7,000 rpm — and had a higher compression ratio — 11.3:1 in comparison to 10.5:1.
Unsurprisingly, the S52 produced lower power and torque figures with 240 hp at 6,000 rpm and 236 lb-ft of torque at 3,800 rpm.
Living With a BMW S50 Engine
The BMW S50 engine is a high-revving, performance-oriented machine. And like most engines that fall under this category, it can be pretty unreliable. A high-performance engine is typically subject to much more challenging driving conditions and will likely run into mechanical issues sooner than a utilitarian counterpart.
In that regard, the U.S. market did dodge a bullet with the S50 engine. Sure, the added reliability of the S52 doesn’t compensate for its lack of sheer performance, but the North American E36 M3s seem to have aged much better than their European counterparts. This is why they’re still quite popular in the pre-owned market.
Even at the time of launch, the S52-powered M3 turned out to be a massive hit. Especially following the (shockingly) dismal sales performance of the original E30 M3 on our shores. As we mentioned above, a few units of the S50 engine have been imported into the U.S., and some were officially brought in across the border in Canada. If you somehow find yourself with the opportunity to own one, here’s what you should keep an eye out for:
Water Pump Failure
Water pump failures are common with BMW engines from the era, and the S50 was one of the more problematic units. The water pump plays a crucial role in the normal functioning of an engine as it regulates its running temperature, irrespective of ambient conditions. While the water pump on the S50 engine is relatively durable, it comes with a plastic impeller known to fail prematurely. The same plastic impeller design is present on many US-spec engines.
BMW decided to use a plastic impeller instead of a metal one since it’s lighter and requires less energy to run. However, this increase in efficiency comes at the cost of durability. If your water pump fails, the engine will overheat at highway speeds, and you might also notice a steady whine from the engine bay.
When it’s time to swap out the stock impeller, try and find an aftermarket replacement made from metal. You won’t notice any changes in performance, but it should last you notably longer.
Cooling System Problems
The S50 also came with an unreliable cooling system. Sadly, the faulty component can sometimes be hard to pinpoint, so cooling system issues with the S50 engine are always a nightmare to deal with.
If you ever have to rectify cooling system-related issues with this engine, the most sensible place to start would be the thermostat, fan clutch, coolant expansion tank, and radiator housing.
The plastic radiator casing is prone to cracking and leaking coolant. Another weak point is the coolant expansion tank — pressurized and made from plastic.
Valve Cover and Gasket Oil Leaks
Nearly every engine that has left the Bavarian giant’s R&D division recently has encountered problems with the plastic valve cover and the rubber gasket. These components are bound to degrade over time, but on engines like the S50 engine, they have been known to have slightly shorter life spans.
These components operate through several heat cycles, reaching extremely high temperatures. As a result, the valve cover and gasket eventually harden and split, letting oil leak.
Fortunately, it’s relatively easy to detect an oil leak around the valve cover. There will be leaks at the front and the sides of the cover. Check for an oil leak if you see oil on the ground beneath the engine compartment, the smell of burning oil inside the cabin, or a thick white smoke coming from the car’s hood.
BMW S50 Engine — The Motor that Got Away?
The BMW S50 is undoubtedly the more exciting of the two engine families that powered the BMW E36 M3. Even today, you’ll find thousands of enthusiasts who are still not over the fact that the German marquee didn’t sell the Euro-spec M3 in our market. However, the S50 engine has its own share of flaws, and when it comes to long-term reliability and resilience, the less capable S52 reigns supreme.
It’s unlikely you’ll ever get to experience the S50 on American soil, but the silver lining is that this is one of the few engines that BMW did not release over here. There’s still an extensive list of sublime Bimmer engines that we can easily access.
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