BMW has been in the business of manufacturing automotive engines since 1928. Over nearly a century, the Bavarian giant has designed and developed engines of various configurations and sizes. However, what it’s most renowned for is its inline-six engines. Some noteworthy examples from recent times include the turbocharged B58 that powers several models in BMW’s current portfolio, and the BMW N52, one of the last naturally-aspirated inline-six units that the company produced.
These engines came packed with technology, most of which was first introduced on one from the ‘90s — the M50 engine. Produced from 1990 to 1996, the M50 engine holds a special place in BMW history as it symbolized the point when BMW started manufacturing more technologically advanced machines.
Today, owning an M50 engine-powered car can be a rewarding experience if you look after it. Finding one in a decent shape is becoming increasing difficult as time goes by — but it’s not impossible! This comprehensive guide looks at every iteration of the M50 engine, what it offers, and what you should look for before buying one.
BMW M50 Engine Design
The M50 engine was the successor to the M20. Like the M20, it was made with an iron engine block and aluminum alloy cylinder heads. However, it introduced several significant updates that are common on today’s Bimmer engines. For instance, it was the first BMW engine to feature a double overhead camshaft (DOHC) with four valves per cylinder. The M20, and every production BMW engine before the M50 engine, featured a single overhead camshaft (SOHC) with two valves per cylinder.
Other notable features on the M50 engine included a coil-on-plug ignition, knock sensor, and a plastic intake manifold lighter than the ones used on engines before.
In September 1992, a couple of years after the M50 engine made its debut, the German manufacturer upgraded it to the M50TU (Technical Update). This engine iteration also holds a consequential place in BMW’s engine history — it was the company’s first engine to feature variable valve timing, or VANOS as we know it now. The system actuated only the phasing of the intake camshaft, unlike more modern BMW engines that do it for the exhaust cams as well.
BMW M50 Engine — Available Versions
Over its production run, the M50 engine was available in five versions, barring the high-performance S50 engines that powered the E36 M3. The standard engines had three different displacements — 2.0L, 2.4L, and 2.5L. Of these, the 2.4L iteration was sold only in select markets, and North America was not one of them.
The 2.0L M50B20 engine and 2.5L M50B25 were introduced in 1990 and would be replaced by their ‘Technical Update’ versions — the M50B20TU and M50B25TU, respectively — in 1992. These four engines made their way to the U.S. and Canadian markets.
The 2.4L M50B24TU engine, meanwhile, was made available only alongside the other two TU engines in 1992.
M50B20
The M50B20 displaces 1,991 cc with bore and stroke figures of 80 mm and 66 mm, respectively. With a compression ratio of 10.5:1, peak output figures were rated at 148 hp at 6,000 rpm and 140 lb-ft of torque at 4,700 rpm.
M50B20TU
The M50B20TU was introduced in 1992 as a replacement for the M50B20, and the update saw the introduction of single-VANOS. While it displaced an identical 1,991 cc, the compression ratio increased to 11.0:1.
Interestingly, peak output figures remained unchanged, but the introduction of VANOS made them available lower in the rev band. Maximum power of 148 hp was produced at 5,900 rpm, while peak torque of 140 lb-ft was now available at 4,200 rpm.
M50B24TU
Displacing 2,394 cc, the M50B24TU was a special iteration of the engine sold only in Thailand and Oceania markets. The M50B24TU is essentially a downsized version of the M50B25TU, thanks to a shorter stroke — 72 mm down from 75 mm.
With a compression ratio of 10.5:1, it produced 185 hp at 5,900 rpm and 177 lb-ft of torque at 4,200 rpm.
M50B25
With a bore of 84 mm and stroke of 75 mm, the M50B25 displaced 2,494 cc. Along with the M50B25TU that replaced it, this was the largest variant of the M50 engine. This engine produced 189 hp at 6,000 rpm and 181 lb-ft of torque at 4,700 rpm.
M50B25TU
The M50B25TU is the updated iteration of the M50B25. Like with the M50B20TU, the addition of VANOS saw peak output figures become available earlier on in the rev range. This version of the M50 engine produced 189 hp at 5,900 rpm and 184 lb-ft of torque at 4,200 rpm.
Which BMW Cars Have an M50 Engine?
The M50 engine was introduced aboard the BMW 520i and 525i from the E34 5-series. Eventually, it would make its way onto multiple models from the 3-Series and 5-Series lineups at the time. Listed below are all the cars that the M50 engine powered in the North American market. For simplicity, we’ve excluded the M50B24TU that did not make its way here.
M50B20
The M50B20 powered the BMW 520i (E34) from 1990 to 1992 and the BMW 320i (E36) in 1991 and 1992. This was one of the first iterations of the engine to be sold.
M50B20TU
Like the M50B20, the M50B20TU powered the BMW 320i (E36) and BMW 520i (E34) from 1992 to 1994 and 1992 to 1996, respectively.
M50B25
The larger displacement M50B25 powered the BMW 325i and 325is (E36) in 1991 and 1992, and the BMW 525i and 525ix (E34) from 1990 to 1992.
M50B25TU
The M50B25TU was used on the BMW 325i, 325is (E36) from 1993 to 1995, and the BMW 525i, 525ix (E34) between 1992 and 1996.
Is the BMW M50 Engine Reliable?
In short, yes. BMW M50 is one of the most reliable engines BMW has ever produced. The BMW M50 engine, with an iron engine block, features one of the most robust constructions the German manufacturer has built.
The M50 is from a time when manufacturers made simple and almost rudimentary powertrains compared to what they manufacture today. As a result, they were less complicated and had fewer things that could go wrong.
Pre-Purchase Inspection and Common Problems
While the M50 engine has a solid construction, it’s important to remember that it’s been around for around three decades. Even the most reliable pieces of engineering are bound to suffer from some sort of mechanical issues after being in use for so long. Additionally, while the engine was pretty durable, some of its auxiliary components, like the cooling system, were not as well engineered.
Before you go out and get your hands on an M50 engine, you should know some common problems you might have to deal with. This way, you can avoid getting into a bad deal and know what to look for during your ownership.
Cooling System Problems
The cooling system is one of the most notorious aspects of the M50 engine, and you’ll find several owners who have faced issues with it. Unfortunately, no single component tends to fail, and if the cooling system is causing you problems, you’ll probably have to inspect all of its parts.
That said, starting with the radiator housing, coolant expansion tank, fan clutch, and the thermostat would be a good idea. The radiator housing is made from plastic and can leak coolant if it cracks. Similarly, the coolant expansion tank is another weak spot as it’s a pressurized plastic component that will leak coolant if there’s a crack.
Asking the previous owner to allow you to perform a cold start should let you assess the condition of the cooling system. If you notice any sudden temperature changes or if the engine temperature reading settles above or below normal, there is likely something that has to be checked.
While cooling system parts are not very expensive, figuring out what’s wrong and replacing them can be cumbersome.
Water Pump Failure
A water pump failure is something that troubled several of the older BMW engines. The water pump plays a crucial role in ensuring that the engine stays at a steady operating temperature, irrespective of ambient conditions. While the water pump on the M50 engine will last over 60,000 miles, it features a plastic impeller that has been reported to fail sooner.
A plastic impeller is lighter than a metal unit and thus requires less energy to power. Unfortunately, this effort to increase efficiency comes at the cost of durability. When the impeller fails. The water pump can no longer function as it’s supposed to, and this will cause the engine to overheat.
If you notice that the engine overheats when driving at highway speeds, or if there’s a whining noise around the engine, there may be something wrong with the water pump.
When it comes time to replace the stock impeller, consider getting one that’s made of metal in its place. The change in performance is negligible, but the metal impeller should last you a good while longer.
Valve Cover and Gasket Oil Leaks
Any BMW owner is likely to run into an oil leak from the valve cover. The valve cover is made from plastic, while the gasket is rubber. Both these parts are subject to extreme temperatures and endless heat cycles, causing them to degrade over time. Rubber, specifically, hardens as it’s exposed to repeated heat cycles and eventually cracks.
On the plus side, an oil leak from the valve cover shouldn’t cause serious concern if rectified as soon as it’s noticed. If you see oil around the spark plug bores or the engine cover, your valve cover or its gasket may be cracked. You might also notice oil on the ground where your car was parked or the smell of burning oil inside the cabin. If oil leaks onto one of the high-temperature components around the engine, like the exhaust, it will cause a thick white smoke from the engine bay — a sure-shot way of telling there’s an oil leak.
The oil cover and its gasket are inexpensive, and it’s best to replace them simultaneously.
Faulty Idle Air Control Valve
The idle air control valve is an integral part of every modern-day automobile. It ensures an engine idles at a steady RPM without stalling, irrespective of ambient conditions. Over time, the idle control valve can pick up dirt and grime, restricting airflow to the engine. This can cause several noticeable issues like a rough idle, engine backfiring, and hesitation under load.
While you do have the option of cleaning the valve, that will only delay its inevitable failure. If the idle control valve is faulty, it’s best that you replace it with a new one.
Ignition System Issues
The M50 engine also faced issues with its ignition system, namely the spark plugs and the ignition coils. The M50 engine was the first Bimmer to feature a coil-on-plug ignition system, where each individual spark plug gets its own ignition coil. While this technology improved performance, efficiency, and ignition control, it was still in the nascent stages and had its own share of issues.
With the M50 engine, you may have to replace the ignition coils, and the spark plugs every 50,000 miles or probably even sooner, in some cases. If one ignition coil fails, the rest are likely to follow, and you should consider replacing all of them simultaneously to save on labor costs.
The symptoms of a faulty ignition system include rough idling, slow engine starts, a drop in performance, and engine misfiring.
Get Your BMW M50 Parts at Bimmers.com
The M50 engine is a beautiful piece of Bimmer history and, if looked after well, will run without causing you too much trouble. There are owners out there who have clocked over 300,000 miles on their cars that are still running fine. If you find yourself with an M50 engine needing some work, head over to Bimmers.com.
Bimmers.com has nearly everything you’ll need to restore or maintain an M50 engine with one of the largest inventories of BMW parts in North America. We stock components from well-known OEM brands and reputed aftermarket names in the industry.
Just head to the website and enter the year and model of your car — we’ll only show you parts that are a perfect fit.
