Engine Coolant Thermostat Guide for the 1987-1989 BMW M6
Keep your high-performance S38 engine running at the perfect temperature by understanding and choosing the right thermostat.
- The correct thermostat for the M6's S38 engine is rated for 80°C (176°F). Using any other temperature will harm performance.
- A thermostat stuck closed is a critical emergency that can destroy your engine; pull over immediately if the temperature gauge spikes.
- For reliability, it is highly recommended to use an OEM-supplier brand like Mahle, Behr, or Vernet-Calorstat.
- There are no recalls or TSBs from BMW or the NHTSA for the thermostat on the 1987-1989 M6.
Symptoms of a Failing Thermostat in Your M6
A thermostat typically fails in one of two ways: stuck closed or stuck open. The symptoms for each are very different.
Thermostat Stuck Closed (Critical)
This is the most dangerous type of failure. The thermostat fails to open, trapping coolant within the engine block and preventing it from reaching the radiator. Heat builds up rapidly, leading to severe overheating.
- Temperature Gauge Spikes to Red: The needle will move quickly into the red zone, often within minutes of driving.
- Steam from Under the Hood: As the trapped coolant boils, pressure builds and can escape as steam.
- Engine Overheating Warning Lights: Your dashboard will alert you to the critical temperature.
Thermostat Stuck Open
This failure is less dangerous to the engine but still causes problems. The thermostat remains open, allowing coolant to circulate through the radiator constantly.
- Engine Takes Too Long to Warm Up: The temperature gauge may never reach the normal center position, especially in cooler weather or during highway driving.
- Poor Fuel Economy: The engine management system thinks the engine is still cold and runs a richer fuel mixture, wasting gas.
- Weak Cabin Heater: Since the engine isn't reaching its full operating temperature, the air blowing from your heater may only be lukewarm.
Choosing the Right Aftermarket Thermostat
For a precision machine like the S38 engine in your M6, not all aftermarket parts are created equal. The cooling system is not a place to cut corners. The most important specification is the 80° Celsius (176° Fahrenheit) opening temperature. Using a thermostat with a different temperature rating can negatively affect performance and efficiency.
Brand Quality Tiers
- Best (OEM Supplier): Mahle, Behr, Hella, Vernet-Calorstat. These brands are trusted in the BMW community for providing original-equipment quality and fitment. They are the recommended choice for reliability.
- Mid-Grade (Use with Knowledge): Beck Arnley. This brand often repackages parts from various manufacturers, which can include OEM suppliers. However, the quality can be inconsistent, as you don't always know the original source of the part inside the box.
- Economy (Use with Caution): Gates, Motorad. While Gates is a reputable brand for other components like belts, their thermostats receive mixed reviews. Motorad is generally considered a budget-tier brand, and some owners report premature failures. For a critical part on an M6, it's generally advised to spend a few extra dollars for a higher-quality unit.
Cost of Replacing Your M6 Thermostat
Replacing the thermostat is a relatively inexpensive job. The primary costs are the part itself and about one to two hours of labor if you take it to a shop.
| Item | Estimated Cost |
|---|---|
| New OEM-Supplier Thermostat (Mahle, Behr) | $18 - $40 |
| New Aftermarket Thermostat (Gates, Beck Arnley) | $18 - $75 |
| Shop Labor | $120 - $240 |
Frequently Asked Questions (FAQ)
What is the correct temperature thermostat for my 1987-1989 M6?
You must use an 80°C (176°F) thermostat. This is the original specification for the S38 engine and is required for proper engine management, performance, and fuel economy.
Is it worth paying more for a Genuine BMW or OEM-supplier thermostat?
Absolutely. The price difference between a budget aftermarket part and a high-quality OEM supplier like Mahle or Behr is often less than $20. Considering the critical role of the thermostat in protecting your valuable S38 engine, it is a worthwhile investment in reliability and peace of mind.
Are there any recalls for the thermostat on my M6?
No. Searches of NHTSA records and technical service bulletins show no recalls or specific TSBs related to the engine coolant thermostat for the 1987-1989 BMW M6.
Can I replace the thermostat myself?
Yes, this is a very DIY-friendly job for someone with basic mechanical skills and tools. The process involves partially draining the coolant, removing the thermostat housing, swapping the part, and then refilling and bleeding the air from the cooling system. The most common difficulty is properly bleeding the system to avoid air pockets.
Technical Specifications
OEM Part Numbers: 11531307737
Opening Temperature: 80° Celsius (176° Fahrenheit)
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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.
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