The E39 M5: A Benchmark that Demands Upgrades

The BMW E39 M5, powered by the iconic S62 V8, remains a high-water mark for sports sedans. Its blend of luxury, handling, and raw power sets a standard that later models still chase. However, two decades of real-world use have exposed specific weak points in the engine bay. The timing chain system and the cooling system are the most common sources of failure. Addressing these areas with carefully selected upgrades transforms the M5 from a rewarding but occasionally fragile machine into a reliable, daily-drivable powerhouse.

This guide cuts through the myths and provides a clear roadmap for strengthening these critical systems. We cover the root causes of failure, the best aftermarket solutions, and the installation steps that matter most. Whether you are building a track-day tool or preserving a collector-grade example, these improvements will keep your S62 running strong for another 200,000 miles.

Timing Chain System: The S62′s Achilles’ Heel

The S62 V8 uses a single-row timing chain guided by two hydraulic tensioners. While the chain itself is robust, the supporting components are not designed for the long haul. The primary failure points are the plastic guide rails and the tensioner bodies. As the guides age, they become brittle and crack. A broken guide can allow the chain to skip teeth, causing immediate valve-to-piston contact and catastrophic engine failure.

Additionally, the lower chain tensioner—often overlooked during routine service—can lose its internal pressure. This results in chain slap at idle and erratic timing under load. The first sign of trouble is a rattling noise from the front of the engine, especially on cold starts. Ignoring that noise is a gamble with a five-figure repair bill.

To bulletproof the timing system, replace the following parts with upgraded or OEM-+ items:

  • Chain Guide Rails: Use the latest BMW part number (11311439728) for the upper left guide. This version has reinforced plastic that resists cracking. For the lower guides, consider the updated BMW guide rails that accept the thicker chain design.
  • Timing Chain: The OEM Iwis chain is excellent, but if the engine has over 150,000 miles, replacement is wise. Some owners upgrade to a VAC Motorsports heavy-duty chain kit that includes a duplex chain conversion. This is a significant upgrade but requires custom machining of the cam sprockets.
  • Tensioners: Install the Beisan Systems upgraded tensioner kit. It uses a higher-pressure spring and a precision-machined housing to maintain consistent tension. This eliminates start-up rattle and maintains timing accuracy.
  • Oil Pump Chain: The oil pump chain is driven by the timing chain and can fail. Replace the oil pump chain and its tensioner with the M5-spec parts from the E60 M5 (part 11417622817) which are stronger.

When ordering a timing chain kit, ensure it includes the updated bolts for the cam sprockets (stretch bolts that must be replaced). Also, buy a new crankshaft hub bolt—it is one-time-use and critical for maintaining proper torque.

Installation Best Practices

Timing chain work on the S62 is not a beginner job. The engine must be locked at top dead center using the proper tools: a cam alignment tool set (available from BimmerWorld). The front cover, oil pan, and vibration damper must be removed. When reinstalling the new guides, apply a thin layer of RTV silicone to the joint between the upper and lower crankcase sections—this area is a known oil leak point.

Torque the cam sprocket bolts to 20 Nm plus 50 degrees. Use a digital torque angle gauge for precision. After assembly, prime the oil system by turning the engine over by hand with the fuel pump relay removed. This floods the new tensioners with oil before the first start.

Cooling System: Preventing Overheating Under Load

The E39 M5’s cooling system is adequate for stock power, but it becomes marginal when driving hard on a hot day or after adding performance modifications. The S62 runs hot (thermostat opens at 105°C/221°F) to reduce emissions, but that temperature accelerates plastic degradation in the expansion tank, radiator, and water pump impeller. A cooling system failure at speed can warp the aluminum heads and blow the head gaskets.

Upgrading to a more robust cooling system is the single most effective reliability improvement you can make. It not only prevents failure but also provides a safety margin for spirited driving and track events.

Common Failure Points

  • Expansion Tank: The OEM plastic tank cracks at the seam, usually around 60,000-80,000 miles. Replace with a Zionsville Autosport aluminum expansion tank. It has a sight glass and a high-quality cap. It reduces under-hood temperatures and eliminates plastic failure.
  • Water Pump: The stock water pump has a plastic impeller that can separate from the shaft. Replace with a Stewart Components high-flow water pump. It features a billet impeller and a lifetime warranty. This pump flows 30% more coolant at idle and 15% more at high RPM.
  • Radiator: The stock radiator’s plastic end tanks crack. Replace with a full-aluminum radiator from Mishimoto or Zionsville. The Zionsville unit includes an integrated transmission cooler for automatic models and a high-capacity core that sheds heat faster.
  • Thermostat: The OEM thermostat can stick open or closed. Install a BimmerWorld 80°C low-temp thermostat. It keeps engine temperatures 25°C cooler under load, which reduces heat soak and knock tendency. Pair it with a 1.4-bar radiator cap to prevent boiling.
  • Coolant Hoses: All rubber hoses harden and crack. Replace with a silicone hose kit from Samco Sport. The silicone hoses resist bursting and last the life of the car. Replace the plastic expansion tank return pipe with a brass or aluminum unit—it is notorious for snapping.

System Integration and Maintenance

After upgrading the radiator, water pump, and expansion tank, you must bleed the system correctly. The S62 has a high point in the cylinder head crossover pipe that traps air. Use a vacuum bleeder or tilt the car nose up while filling. Run the engine with the heater on full hot to purge all air pockets.

Use BMW-approved blue coolant or a high-quality phosphate-free OAT coolant. Do not mix coolants—it can gel and block the heater core. Change the coolant every two years or 30,000 miles, whichever comes first. At the same interval, inspect the belt tensioner and idler pulleys; a seized pulley can throw the serpentine belt and cause an immediate overheat.

For track use, consider adding an electric fan conversion kit from Mishimoto. It pulls more air through the radiator at low speeds and frees up parasitic drag. However, ensure the fan controller has a manual override switch so you can run the fan after shutdown to prevent heat soak.

Scheduled Maintenance Intervals

The following table lists the recommended service intervals for the reliability-upgraded E39 M5. These intervals assume upgraded components are installed. If you still have stock parts, reduce the intervals by 50%.

  • Every 15,000 miles: Change engine oil (10W-60, Castrol TWS or equivalent). Replace oil filter. Inspect coolant hoses and expansion tank for cracks.
  • Every 30,000 miles: Change coolant. Replace the thermostat (use 80°C performance unit). Inspect water pump for weeping. Replace serpentine belt and tensioner.
  • Every 60,000 miles: Replace the expansion tank (if not aluminum). Replace all coolant hoses (or upgrade to silicone at this point). Inspect timing chain for stretch by measuring cam-to-crank correlation using diagnostic software (INPA or ISTA).
  • Every 100,000 miles: Replace timing chain, guides, and tensioners. Replace oil pump chain. Replace the harmonic balancer (vibration damper) – rubber separates and can throw the belt or damage the crank hub.

If you are starting from square one with a high-mileage car, perform all of the above at once. It simplifies ownership and ensures every critical component is new.

Cost vs. Benefit Analysis

A full timing chain overhaul (parts and labor at an independent shop) runs between $3,500 and $5,000. A full cooling system upgrade (aluminum radiator, water pump, expansion tank, silicone hoses, low-temp thermostat) costs approximately $1,200 in parts and $600 in labor. Compare that to the cost of a replacement S62 long block: $8,000 used, $15,000 rebuilt. The math is clear—preventative upgrades are the most cost-effective way to keep the E39 M5 on the road.

Beyond reliability, these upgrades improve performance. A lower coolant temperature allows more aggressive ignition timing, which translates to better throttle response and a few extra horsepower. The aluminum expansion tank and silicone hoses also reduce engine bay temperatures, protecting rubber seals and electronics. The engine simply runs happier.

Common Mistakes to Avoid

  • Using cheap aftermarket parts: Stick with OEM suppliers (INA, Iwis, Graf, Hella) or known performance brands (VAC, Stewart, Beisan, Zionsville). eBay specials fail quickly.
  • Skipping the oil pump chain: Many DIYers replace the timing chain but leave the oil pump chain. It is driven by the same system and fails at similar mileage. Replace it.
  • Not bleeding the cooling system properly: Air trapped in the S62 causes local hot spots that can crack the cylinder head. Use a vacuum bleeder or the BMW bleeding procedure (ignition on, heater full hot, fan at low speed, open bleeder screw until no bubbles).
  • Forgetting the valley pan gasket: While the intake manifold is off for cooling work, replace the valley pan gasket and the rear coolant pipe O-rings. It is a known leak that can only be fixed with intake removal.
  • Ignoring the CCV (crankcase ventilation): A failed CCV can pressurize the crankcase and push oil past the rear main seal. While the engine is open for timing chain work, replace the CCV diaphragm and hoses.

Final Verdict

The BMW E39 M5 is a legend, but it requires informed ownership. The timing chain and cooling system are not optional upgrades—they are mandatory for anyone who plans to drive the car hard or keep it long-term. By investing in the parts and procedures outlined here, you eliminate the two most common failure modes of the S62 engine. The result is a car that feels tighter, cooler, and more responsive than the day it left the factory. Drive with confidence.