A Guide to the Engine Coolant Thermostat for the 2000-2005 BMW M5
Understanding how this critical part works on your S62 engine and how to choose the right replacement.
- The most common failure is stuck-open, causing a cold-running engine, poor MPG, and a P0128 code.
- For this specific vehicle, it is highly recommended to use an OEM-equivalent brand like Behr or Mahle for reliability.
- Replacement is a complex DIY job due to the need to remove VANOS lines and intake components to access the thermostat.
- Always replace the associated gaskets and O-rings with the thermostat to prevent leaks.
Signs of a Failing Thermostat in Your M5
The thermostat in the E39 M5 is designed to fail in the "stuck open" position as a safety measure to prevent catastrophic overheating. While this is better than failing closed, it still causes problems. Here are the most common symptoms you'll notice:
- Engine Takes Too Long to Warm Up: This is the most frequent sign. You'll notice the temperature gauge on your dashboard takes much longer than usual to reach the center position, or it may not reach it at all during highway driving.
- Poor Fuel Economy: When the engine runs cooler than it should, the engine computer (DME) compensates by running a richer fuel mixture, which hurts your gas mileage.
- Check Engine Light: A thermostat that is stuck open or not performing correctly can trigger a fault code, such as P0128 (Coolant Temperature Below Thermostat Regulating Temperature), illuminating the check engine light.
- Reduced Heater Performance: Your car's cabin heater uses heat from the engine coolant. If the engine isn't getting hot enough, your heater will blow lukewarm air, which is especially noticeable in winter.
Overheating Is Still Possible
Though rare, a thermostat can fail in the closed position. This is a critical situation. If you see your M5's temperature gauge enter the red zone, pull over immediately and shut off the engine to prevent severe damage like a warped cylinder head or failed head gasket.
Choosing the Right Aftermarket Thermostat
For a high-performance and complex vehicle like the E39 M5, part quality is crucial. While a Genuine BMW part is always an option, high-quality OEM-equivalent parts offer the same performance without the high dealership price.
OEM vs. Aftermarket Quality:
For many BMWs, including the E39 M5, brands like Behr and Mahle are the Original Equipment Manufacturers (OEM). This means they produced the original part for BMW. Choosing an OEM part from one of these brands is often the most reliable and cost-effective strategy, as it's virtually identical to the genuine part. When it comes to the available aftermarket brands for your M5:
- Tier 1 (OEM-Equivalent): Brands like Calorstat (by Vernet) are often considered OEM suppliers for many European vehicles. They are generally a reliable choice. Forum discussions for BMWs frequently recommend sticking with OEM suppliers like Behr or Mahle for critical cooling system parts.
- Tier 2 (Standard Aftermarket): Gates and Motorad are well-known aftermarket brands. While they produce a wide range of parts, owner experiences can be mixed. For a specialized vehicle like the M5, the consensus among enthusiasts is to prioritize OEM-spec parts to ensure proper function of the map-controlled system and avoid premature failure.
Pro Tip: Given the complexity of the replacement job and the critical function of the thermostat, spending a little more on an OEM-equivalent brand like Behr or Mahle is a wise investment to avoid doing the job twice.
Known Issues, Recalls, and Service Bulletins
A search of the National Highway Traffic Safety Administration (NHTSA) database and technical service bulletins (TSBs) did not reveal any specific recalls or TSBs for the engine coolant thermostat on the 2000-2005 BMW M5. However, there is a major, unrelated safety recall for defective Takata airbags affecting these models that owners should be aware of.
| Part Type | Estimated Cost |
|---|---|
| New OEM (Mahle/Behr) | $65 - $140 |
| New Aftermarket (Gates, Motorad, etc.) | $39.69 - $118.16 |
| Shop Labor | $455 - $668 |
Frequently Asked Questions (FAQ)
Can I drive my M5 with a bad thermostat?
If it's stuck open, you can drive short distances, but it's not recommended for long. The engine will run too cool, leading to poor fuel economy, increased emissions, and accelerated engine wear. If it's stuck closed, you should not drive the car at all, as it will overheat very quickly.
How difficult is it to replace the E39 M5 thermostat?
This is a moderately difficult job for a DIY mechanic. It requires removing the intake plenums and VANOS oil lines to access the thermostat housing. It is a more involved process than on most other cars and requires care to avoid damaging seals and components.
What other parts should I replace with the thermostat?
It is highly recommended to replace the thermostat housing gaskets and the O-rings for the three short alloy tubes that connect to the housing. Many owners also choose to replace the water pump at the same time if it has high mileage, as it is located nearby. Using new coolant is also a must.
What is a "map-controlled" thermostat?
A map-controlled thermostat has an internal electric heating element. The engine computer (DME) can heat this element to make the thermostat open sooner or at a lower temperature than its mechanical set point. This allows the DME to precisely manage engine temperature based on driving conditions, balancing fuel economy (hotter temp) and power (cooler temp).
Technical Specifications
OEM Part Numbers: 11537835558 11531315063 11531407772
Map-controlled electronic thermostat. Opening temperatures vary based on electronic control, with a mechanical failsafe.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- BMW M5: