The BMW F90 M5 is a technological marvel, packing a twin-turbocharged 4.4L V8 (S63 engine) that delivers breathtaking performance straight from the factory. However, as with any high-strung performance machine, sustaining that level of power reliably over the long term requires a proactive approach. Heat management, internal component strength, and disciplined maintenance are the three pillars that separate a well-loved daily driver from a costly repair bill. This guide dives deep into the most effective reliability upgrades for the F90 M5, focusing on cooling systems, bearings, and the critical maintenance habits that will keep your M5 on the road and off the lift.

The Heat Problem: Why Cooling Upgrades Are Non-Negotiable

The S63 engine runs incredibly hot. BMW designed it for performance, but the thermal load from the twin turbos coupled with the high compression ratio means heat soak and elevated oil temperatures are common during spirited driving or track sessions. Factory cooling is adequate for normal use, but any sustained high-rpm operation will quickly expose its limits. Overheating can lead to detonation, head gasket failure, and accelerated wear on every rotating component. Upgrading the cooling system is the single most impactful reliability investment you can make.

Upgraded Radiator

The factory radiator is a single-row aluminum unit that works fine in most climates. However, when ambient temperatures rise or you begin pushing the car hard, the cooling capacity becomes a bottleneck. An upgraded radiator (such as those from CSF or Mishimoto) uses a thicker, multi-row core and often a more efficient fin design. This directly reduces coolant temperatures by 10–20°F under load. For those who see regular track time or live in hot climates (Arizona, Texas, Middle East), this is a must-have. The installation is straightforward and does not require any permanent modifications, making it a bolt-on upgrade that immediately pays dividends.

High-Capacity Oil Cooler

Oil temperature is arguably more critical than coolant temperature. The factory oil cooler is sufficient for daily driving, but it can struggle to keep oil below 250°F during repeated full-throttle runs. When oil exceeds 280°F, its viscosity drops, lubricating properties degrade, and internal clearances become a risk. An aftermarket oil cooler with a larger core (e.g., from CSF or Wagner Tuning) adds more volume and surface area. Some kits also include a thermostat that opens at a lower temperature to keep oil cooler in all conditions. This reduces wear on bearings, turbos, and the timing chain.

Intercooler Upgrade

The S63 uses air-to-water intercoolers. The factory intercoolers are adequate for stock power levels, but they suffer from heat soak quickly—especially during back-to-back pulls. Upgraded intercoolers (such as those from CSF, Wagner, or RaceChip) feature larger cores and more efficient flow paths for the coolant that passes through them. This lowers intake air temperatures (IATs) by 15–30°F, which not only increases power (cooler air is denser) but also reduces the risk of pre-ignition and detonation. Lower IATs also mean the engine management system doesn’t have to pull timing to protect the engine, so you get consistent performance lap after lap.

Lower-Temperature Thermostat

A simple but effective upgrade is swapping the factory thermostat for a lower-temperature unit (typically 160°F or 170°F instead of the stock 200°F). This forces the engine to operate at a cooler baseline temperature, which creates more headroom before critical temperatures are reached. It also reduces the overall thermal stress on the cooling system components. Be aware that the engine may take slightly longer to reach operating temperature in cold climates, but the trade-off is well worth it for performance-oriented use.

Electric Auxiliary Water Pump

The S63 uses an electric water pump for post-shutdown cooling (the pump continues to circulate coolant after the engine is turned off to prevent hot spots). Upgrading to a higher-flow electric pump (e.g., the EMP Stewart pump) improves coolant flow at low RPM and during idle, significantly reducing the risk of air pockets and improving heat transfer. This is especially beneficial if you have an upgraded radiator and intercoolers, as it ensures the coolant moves quickly enough to take full advantage of the larger cores.

Bearings: The Achilles' Heel of the S63

The S63 V8 in the F90 M5 shares a design characteristic with many BMW performance engines: connecting rod bearings that are designed for a balance of cost, noise, and performance but not necessarily for extreme long-term durability. While the S63 rod bearings are more robust than earlier N63 units, they are still a known failure point if the car is tracked heavily, tuned aggressively, or if oil change intervals are stretched. Upgrading to performance bearings is one of the most proactive reliability modifications you can undertake.

Understanding Rod Bearing Failures

Rod bearing failures occur when the thin layer of bearing material (typically a lead-copper or aluminum-tin alloy) wears through, allowing metal-to-metal contact between the rod and the crankshaft journal. This can lead to a spun bearing, which often results in catastrophic engine failure. Contributing factors include: high oil temperature, extended oil change intervals, overly thin oil viscosity, and sustained high loads. The F90 M5’s torque curve and twin-turbo setup create immense stress on the bottom end, making bearing upgrades a wise investment.

Aftermarket bearings like Clevite 77 or ACL Race Series bearings are manufactured with a harder, more durable tri-metal construction. They have a higher load-carrying capacity and better fatigue resistance compared to the OEM bearings. Some builders opt for King Racing bearings or WPC (World Pac Copper) treated bearings, which have a surface coating that reduces friction and provides an extra layer of protection during dry starts. The installation requires removing the oil pan and the connecting rod caps, so it's typically done during a major service or engine rebuild—but the peace of mind is significant.

Main Bearings and Thrust Bearings

While rod bearings get the most attention, the main bearings and thrust bearings also benefit from upgrades. Main bearings support the crankshaft; upgrading them reduces friction and can improve oil pressure. Thrust bearings handle axial loads from the torque converter or clutch. If you plan on higher boost levels or have an automatic transmission with high stall converter, consider replacing these with performance units. Many bearing upgrade kits include all three sets (rod, main, thrust) for a complete bottom-end refresh.

Turbocharger Bearings

The S63’s twin turbos spin at speeds exceeding 150,000 RPM. The factory journal bearings can degrade over time, especially if oil is contaminated or if there are frequent hot shutdowns. Upgrading to ceramic ball bearings or hybrid ball bearings in the turbochargers reduces friction and spool time while also improving durability at high shaft speeds. Some companies offer rebuilt or upgraded turbo cartridges with better bearings. If you are replacing turbos due to wear or upgrading to larger units, it’s an ideal opportunity to specify ceramic bearings. Companies like Boost Logic and Pure Turbos offer upgraded turbo options for the F90 M5.

Maintenance Tips That Make or Break Reliability

Even with the best aftermarket parts, neglecting regular maintenance is the fastest way to destroy an S63 engine. The F90 M5 is not a Toyota Camry—it demands strict adherence to service intervals and a willingness to go beyond the factory recommendations.

Engine Oil: Frequency and Specification

BMW recommends oil changes every 10,000 miles (or annually) with 0W-30 LL-01 FE or 5W-30 LL-01. For reliability, cut that interval in half. Change oil every 5,000 miles or every 6 months, whichever comes first. Why? Because the S63 dilutes oil with fuel due to the direct injection system, and high heat degrades the additive package quickly. Use a high-quality synthetic like Liqui Moly Leichtlauf High Tech 5W-40 or Motul 300V 5W-40. These oils have a higher viscosity index and better shear stability. If you track the car, consider 5W-50 or 0W-50 to maintain oil pressure at extreme temperatures.

Coolant Service: Not Just Water

BMW’s blue coolant is phosphate-free and designed for aluminum engines. Flush the coolant every 2 years or 30,000 miles—not the 4-year interval the manual suggests. Use distilled water mixed with BMW-approved coolant or a high-performance option like Evans Waterless Coolant, which eliminates the risk of electrolysis and boil-over. Before each long drive, check the coolant level in the expansion tank (cold). Low coolant can cause air pockets that lead to localized overheating.

Spark Plugs and Ignition Coils

The S63 uses twin-scroll turbos and high boost, which puts a lot of stress on spark plugs. Replace spark plugs every 20,000 miles (the factory interval is often 40,000+). Use NGK 97506 (LKR7AI) or equivalent gapped to 0.022″ for tuned cars. Ignition coils can fail under high heat; replace them at 50,000 miles with OEM or performance coils (e.g., Bosch or Eldor). Misfires due to weak coils can dump raw fuel into the exhaust, damaging catalytic converters and O2 sensors.

Belts and Pulleys: Preventative Replacement

The serpentine belt drives the alternator, A/C, and water pump. The belt can fray or slip, and the tensioner bearings can fail. Inspect the belt every 10,000 miles for cracks or glazing. Replace it (along with the idler pulleys and tensioner) every 40,000 miles or 4 years. A broken belt can get sucked into the engine through the front main seal, causing catastrophic damage. Use Gates or Continental belts.

Fuel System: Keep It Clean

Direct injection means the intake valves do not get washed by fuel, leading to carbon buildup. Use a quality catch can to reduce oil vapor recirculation (a BMS or ADD W1 catch can is recommended). Perform intake valve walnut blasting every 30,000–40,000 miles. Also, use top-tier gasoline (Shell V-Power NiTRO+, Chevron 93, etc.) to minimize deposits on injectors and inside the combustion chamber. If you tune the car, a port injection system can help keep valves clean while also adding fuel capacity for higher horsepower.

Differential and Transmission Fluid

The F90 M5 uses an automatic transmission (ZF 8HP76) and an active M differential. The transmission fluid and filter should be changed every 50,000 miles—BMW calls it “lifetime,” but that’s not realistic for a performance car. Use ZF Lifeguard 8 or equivalent for the transmission. The differential fluid (75W-140 synthetic) should be changed every 30,000 miles. Neglecting these fluids leads to rough shifts and diff whine.

Brake Fluid and Pads

Stock brakes are excellent, but high-temperature fluid is essential for reliability. Use Motul RBF 660 or Castrol SRF, which have dry boiling points above 600°F. Flush brake fluid annually—brake fluid absorbs moisture, which lowers the boiling point and can cause brake fade or even fluid vaporization under hard stops. Pad selection matters: for track use, Pagid RSC1 or Ferodo DS2500 offer consistent bite and high temperature tolerance.

Tuning Considerations for Reliability

Given the F90 M5’s immense tuning potential, many owners flash the ECU for Stage 1 or Stage 2 power levels. While the S63 can handle extra power, reliability requires a holistic approach. Always combine a tune with cooling upgrades and a conservative boost strategy. Avoid aggressive ignition timing that increases cylinder pressure excessively. A custom dyno tune from a reputable shop like Epifan Tuning or Performance Eurowerks can optimize air/fuel ratios and timing for safety. Additionally, a flex fuel kit (E85 blend) can lower combustion temperatures and allow more timing advance while reducing knock risk—but only if the fuel system and injectors are upgraded.

Drivetrain Durability: Upgrading Motor Mounts and Transmission Mounts

Under hard acceleration, the S63’s torque twists the engine on its rubber mounts. Worn motor mounts allow excessive movement, which can stress the cooling hoses, intercooler piping, and even the exhaust manifolds. Upgraded polyurethane or race-style motor mounts (e.g., from BFI or Rogue Engineering) keep the engine firmly in place, improving shift quality and reducing the risk of component contact. Similarly, stiffer transmission mounts reduce drivetrain lash and enhance the feel of the ZF 8HP, particularly during fast gear changes.

Conclusion: A Roadmap to Long-Term F90 M5 Reliability

The F90 M5 is a masterpiece of engineering, but it is not impervious to the effects of heat, stress, and maintenance neglect. The best reliability upgrades start with the cooling system: a high-capacity radiator, upgraded intercoolers, a larger oil cooler, and a lower-temp thermostat form the foundation. Next, address the internal bearings—rod bearings especially—with performance-grade components to safeguard the bottom end against high loads. Finally, adhere to an aggressive maintenance schedule: halve the oil change interval, use premium fluids, replace spark plugs and belts early, and keep the cooling system fresh. By following these steps, you can enjoy the raw performance of the F90 M5 for many tens of thousands of miles, with confidence that the car will remain reliable under any condition. Whether you are a weekend warrior or a daily driver, investing in these upgrades is an investment in the longevity of one of BMW’s finest creations.