Audi S4 (2010-2016) Engine Coolant Thermostat: A Complete Guide
Keep your S4's supercharged 3.0T engine from overheating by understanding thermostat failure and choosing the right replacement part.
- Thermostat failure is a common and serious issue for the 2010-2016 S4; symptoms include overheating or an engine that runs too cool.
- Replacement is a very labor-intensive job (7+ hours) because the thermostat is located under the supercharger.
- Due to the high labor cost, it is strongly recommended to replace the water pump and PCV valve at the same time as the thermostat.
- If your engine is overheating, stop driving immediately to avoid catastrophic engine damage.
Is Your S4 Thermostat Failing?
The engine coolant thermostat is a known weak point on the 2010-2016 Audi S4 (B8 and B8.5 generations). Because it is located under the supercharger, replacement is a labor-intensive job. For this reason, it's critical to recognize the symptoms early and choose a quality replacement part. Many owners choose to replace the thermostat, water pump, and PCV valve at the same time to avoid paying for the same difficult labor twice.
Symptoms of a Bad Thermostat
A failing thermostat can get stuck in two ways: closed or open. The symptoms are very different for each.
- Engine Overheating (Stuck Closed): This is the most dangerous failure. The temperature gauge will climb into the red, and you may see a "Coolant System: Fault" warning. Your A/C may also stop blowing cold air as the engine gets too hot. If you see these signs, pull over immediately to prevent severe engine damage.
- Engine Slow to Warm Up (Stuck Open): If your car takes a very long time to reach normal operating temperature, or never gets there, the thermostat is likely stuck open. This will hurt your fuel mileage and can trigger a Check Engine Light for code P0128.
- Coolant Leaks: The plastic thermostat housing can crack over time, causing coolant to leak and pool in the valley of the engine, under the supercharger. You might notice a sweet smell of antifreeze from the engine bay or see your coolant level drop. 🎬 See where coolant pools under the supercharger when leaks occur.
Known Issues: TSB and Service Campaign
Audi issued Technical Service Bulletin (TSB) 2040491/1 for 2012-2013 models that could display a "Coolant System: Fault" message due to a defective thermostat. Additionally, a safety recall for a fuel system issue on 2011-2013 models (Recall 24AP) included a provision for dealers to update the thermostat at the same time, free of charge. While there is no direct safety recall for the thermostat itself, these actions show that Audi is aware of the part's potential issues.
Choosing the Right Aftermarket Thermostat
Since replacing the thermostat is so labor-intensive, part quality matters. You don't want to do this job twice. Here’s a breakdown of the available brands.
| Brand Tier | Brands | Our Price | Notes |
|---|---|---|---|
| OEM & OE Supplier | Genuine Audi, Vemo, Gates | $55 - $102 | OEM is the original part your car came with. Vemo and Gates are Original Equipment (OE) suppliers known for making high-quality parts that meet or exceed factory specs. For a critical part like this, they are a reliable choice. |
| Performance Upgrade | Mishimoto | ~$100 | Mishimoto offers a "racing" thermostat that opens at a lower temperature (159.8°F vs. 185°F stock). This can help keep a modified or tracked car running cooler, but it is not necessary for a standard daily-driven S4. |
| Value | URO Parts | $43 - $50 | URO Parts is a budget-friendly option. While their quality has been inconsistent in the past, they can be a viable choice if cost is the primary concern. However, given the high labor cost for this job, most mechanics would recommend a higher-tier brand. |
Pro Tip: Replace More Than Just the Thermostat
The thermostat is located right next to the water pump and PCV valve. All three are common failure items on the 3.0T engine and require removing the supercharger for access. To save thousands on future labor costs, it is highly recommended to replace the thermostat, water pump, and PCV valve all at the same time.
🎬 Watch: Step-by-step guide to replacing the PCV valve while disassembled.Frequently Asked Questions (FAQ)
How much does it cost to replace an Audi S4 thermostat?
At a dealership or independent shop, expect the total cost to be between $1,100 and $1,500. The part itself is not very expensive, but the labor is, typically running from $650 to over $950 because the supercharger must be removed.
Can I replace the S4 thermostat myself?
If you are an experienced DIY mechanic, yes. The job requires removing the supercharger, which is complex. It takes a full day and requires special tools like triple-square sockets. For most owners, this job is best left to a professional.
🎬 Watch: Full DIY walkthrough for replacing the thermostat and water pump.What is the difference between a regular and a racing thermostat?
A racing thermostat, like the one from Mishimoto, is designed to open at a lower temperature than the stock part. This gets coolant flowing to the radiator sooner, which can be beneficial for highly tuned cars or vehicles used on a race track. For a stock or lightly modified S4 used on the street, the standard temperature thermostat is perfectly fine.
My temperature gauge is normal, but I smell coolant. Could it still be the thermostat?
Yes. The plastic housing of the thermostat assembly is a common failure point. It can crack and leak coolant directly into the engine valley, creating a noticeable sweet smell long before it affects the temperature reading.
Helpful Videos
Technical Specifications
OEM Part Numbers: 06E121111AL 06E121111AD 06E121111P 06E121111S 06E121111T
OEM Activation Temperature: 185°F (85°C). Includes integrated housing and seal.
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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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