The BMW E39 M5, powered by the legendary S62 V8, remains one of the most celebrated performance sedans ever built. Its combination of analog driving dynamics, luxurious interior, and a wailing 400-horsepower engine has earned it icon status. However, nearly two decades after production ended, every example on the road is a high-mileage car requiring attentive ownership. Long-term reliability hinges on addressing three critical areas: oil leaks, cooling system vulnerability, and electrical gremlins. By understanding these failure points and adopting a proactive maintenance regimen, owners can keep their E39 M5 performing at its peak for another hundred thousand miles.

Understanding the S62 V8's Common Oil Leak Points

The S62 is a dry-sump engine that uses a separate oil reservoir and external pump. While this design helps prevent oil starvation under hard cornering, it also creates numerous sealing surfaces. Over time, heat cycles cause gaskets and seals to harden and shrink, leading to leaks that can drip onto exhaust manifolds or contaminate belts. Addressing oil leaks early prevents more serious issues like low oil pressure or engine fires.

Valve Cover Gaskets

Valve cover gaskets on the S62 are prone to hardening and cracking. A leaking valve cover gasket often manifests as a burning oil smell from the driver’s footwell or smoke rising from the exhaust manifolds. The replacement process is straightforward but requires care: the plastic covers can warp if overtorqued, so using a torque wrench and new grommets is essential. Many owners upgrade to genuine BMW gaskets or high-quality aftermarket alternatives from Elring or Victor Reinz. While the covers are off, it’s a good time to inspect the spark plug wells for oil intrusion, which can cause misfires.

Oil Filter Housing Gasket

The oil filter housing sits on the front of the engine and connects to the block via a gasket. This is another frequent leak source. The housing itself is made of plastic and can crack with age, but more commonly the gasket hardens, allowing oil to run down the front of the engine, often mistaken for a timing cover leak. Replacing the gasket is a moderate DIY job, but upgrading to an aluminum oil filter housing from a performance supplier eliminates the risk of the plastic housing cracking. When performing this service, also flush the cooler lines and replace the crush washers.

Rear Main Seal and Oil Pan Gasket

The rear main seal (RMS) sits between the engine and transmission. A leak here requires removing the transmission, making it an expensive repair if done at a shop. Symptoms include a drip between the engine and bell housing or oil on the clutch. If you ever need to replace the clutch, it’s wise to proactively replace the rear main seal. The oil pan gasket is also a common leaker, especially on cars that have been driven on rough roads where the pan may have been hit. Because the S62 has a deep aluminum oil pan with integrated baffles, the gasket can shrink over time. Replacing the oil pan gasket requires lifting the engine slightly or dropping the subframe, so many owners address it during other major engine-out services.

Cooling System — The Achilles Heel of the E39 M5

The S62 produces immense heat, and the stock cooling system was designed for a 15-year service life. On today's 20+ year old cars, the cooling system is the single biggest threat to engine reliability. Overheating can warp cylinder heads, blow head gaskets, or destroy the aluminum block. Replacing the entire cooling system proactively every 60,000-80,000 miles is standard advice among enthusiasts.

Expansion Tank, Water Pump, and Thermostat

The original plastic expansion tank is prone to cracking at the seam, especially after heat cycles. A crack often leads to sudden coolant loss. Upgrade to a German-made Behr or an aluminum replacement tank from BimmerWorld for added durability. The water pump on the S62 originally came with a composite impeller that can disintegrate, breaking apart and clogging the cooling passages. Replace it with a pump that has a metal impeller — either from BMW's later production runs or aftermarket brands like Stewart. The thermostat is another known weak point; it can stick open or closed. Use a genuine BMW 92°C thermostat for optimal operating temperature. While you’re in there, replace the thermostat housing (also plastic) and all coolant hoses, including the hard-to-reach heater hoses under the intake manifold.

Upgrading for Longevity

Beyond basic replacement, consider an electric water pump conversion (although rare, it eliminates belt-driven pump failure). Many owners also install an auxiliary electric fan to help cool the engine in traffic or during track days. Flushing the coolant every two years with BMW blue antifreeze keeps the system corrosion-free. A simple pressure test annually can catch developing leaks before they strand you. For those who drive hard, a low-temp thermostat and a higher-capacity radiator (e.g., CSF or Zionsville) can provide a meaningful safety margin.

Electrical Quirks and How to Tame Them

As E39s age, electrical gremlins become more pronounced. The car’s I-bus and K-bus networks route signals to everything from the instrument cluster to the seat heaters. Weak batteries, corroded grounds, and failing capacitors can cause a cascade of strange symptoms. Systematic diagnosis and attention to known weak points keep the electrical system reliable.

Pixel Failure and Instrument Cluster Repair

Nearly every E39 M5 develops dead pixels in the instrument cluster display (odometer, outside temp, radio text). This is caused by a cracked ribbon cable between the LCD driver board and the main cluster board. Repair services are available for around $150–$250, or you can tackle it yourself with a new ribbon kit. While the cluster is out, consider upgrading the capacitors on the circuit board to prevent total failure. Many owners also replace the cluster backlight bulbs with LEDs for a brighter, more modern look.

Battery Drain and Grounding Issues

The E39 is notorious for parasitic draws from the General Module (GM) and the Light Control Module (LCM). A common symptom is a dead battery after sitting for a week. Start by checking the battery condition with a load tester, then measure parasitic draw. Common culprits include a failing GM that won't sleep properly, aftermarket electronics (alarms, stereos) not wired correctly, or a trunk light that stays on. Adding a low-voltage disconnect or a battery tender for long storage helps. Also, inspect the main ground strap from the engine block to the chassis and the ground connections near the battery. Corroded grounds can cause random warning lights, such as the ABS or DSC light coming on.

Sensor Failures and Diagnostics

The S62 uses many sensors that degrade over time. The most frequent are the crankshaft position sensor, which can cause no-start or intermittent stalling, and the mass air flow (MAF) sensors. Both are known to fail, and using non-OEM sensors often leads to poor idle or throttle response. Stick with genuine Bosch or Siemens sensors. The camshaft position sensors can also fail, triggering a check engine light and reduced performance. Another odd electrical issue is the failure of the heater blower final stage resistor, which causes the interior fan to only work on full speed. This module is cheap and easy to replace. Finally, consider investing in a diagnostic tool like INPA or ISTA (or a simple Bluetooth OBD2 adapter with a BMW-specific app) to read fault codes and monitor live data — it’s invaluable for troubleshooting.

VANOS, Suspension, and Supporting Systems

While oil, cooling, and electrical are the top three threats, several other systems require attention for long-term performance. The S62’s VANOS (variable camshaft timing) unit can develop rattle and loss of low-end torque due to worn seals. The common fix is to rebuild the VANOS with upgraded seals (often called the “Beisan” repair). This job takes a full day but restores smooth idle and throttle response. If your engine makes a diesel-like rattle at idle, VANOS seals are likely the culprit.

The E39 M5’s rear subframe and differential mount bushings are another weak point. After 100,000 miles, these rubber bushings become soft, causing wheel hop and vague rear-end feel. Upgrading to polyurethane or aluminum bushings tightens the chassis and improves traction. While you’re under the car, inspect the rear subframe for cracks near the mounting points — a known issue on early E39 M5s. A reinforcement kit from Turner Motorsport or a weld-in reinforcement plate prevents catastrophic failure.

Finally, the 6-speed manual transmission (Getrag 420G) is famously robust, but the clutch and dual-mass flywheel can wear out. Symptoms include clutch shudder or difficulty engaging gears. Replacing with a single-mass flywheel and lighter clutch improves rev response but introduces more gear rattle. Whichever path you choose, stick with quality components from Sachs or Valeo.

Building a Proactive Maintenance Plan

Owning an E39 M5 is a relationship built on prevention. A well-maintained car can easily surpass 200,000 miles, while a neglected one is a money pit. The most important interval is the oil change: use only 10W-60 oil (Castrol TWS or Liqui Moly Synthoil Race Tech) and change every 5,000 miles. This protects the VANOS unit and the high-stress bottom end. Spark plugs should be replaced every 30,000 miles (use NGK BKR6EQUP or equivalent).

Every 60,000 miles, perform the “cooling system overhaul” — replace radiator, expansion tank, water pump, thermostat, all coolant hoses, and belts. The same interval is a good time to refresh the VANOS seals, clean the idle control valve, and replace the fuel filter. For electrical peace of mind, replace the 20-year-old battery with a quality AGM unit, and clean all ground contacts. Budget for a suspension refresh every 80,000–100,000 miles, including control arms, thrust arms, and rear links from Lemförder or Meyle HD.

E39 M5 forums and dedicated communities like M5Board are treasure troves of maintenance logs and DIY guides. Leveraging these resources alongside sourcing parts from reputable suppliers (such as FCP Euro or ECS Tuning) ensures you get the right parts at fair prices.

In conclusion, the BMW E39 M5 demands a steward who respects its engineering excellence and accepts its age. By methodically addressing oil leaks, renewing the cooling system, staying ahead of electrical gremlins, and supporting the rest of the powertrain with proper maintenance, you can enjoy one of the greatest driver’s cars ever built — reliable enough for daily commuting and sharp enough for a weekend canyon run or track day. The key is not to fix things when they break, but to prevent them from breaking in the first place.