Engine Coolant Temperature Sensor for the 2013-2022 Audi S8
Understanding the critical role of the coolant temperature sensor in your S8's 4.0T engine and how to choose the right replacement.
- The Audi S8 has multiple coolant sensors; proper diagnosis is key to replacing the correct one.
- Symptoms include check engine light (P0117, P0118), poor MPG, overheating, and erratic gauge behavior.
- For this critical part, choose premium aftermarket brands like Hella, Vemo, or Delphi for reliability similar to OEM.
- Ignoring a faulty sensor can lead to poor performance and, in a worst-case scenario, severe engine damage from overheating.
Symptoms of a Failing Coolant Temperature Sensor
A failing coolant temperature sensor can cause a range of issues, some of which can mimic other problems. Because the sensor's data is so critical for engine management, a bad signal can lead to noticeable performance changes. Be aware of these common symptoms:
- Check Engine Light: This is often the first sign. A scanner will typically show fault codes like P0117, P0118, P017B, or P2181.
- Poor Fuel Economy: If the sensor incorrectly tells the ECU the engine is cold, the system will run a richer fuel mixture, wasting gas.
- Engine Overheating or Running Cool: A faulty sensor might not trigger the cooling fans to turn on when needed, leading to overheating. Conversely, a false 'hot' signal can cause fans to run constantly and prevent the engine from reaching its optimal operating temperature.
- Erratic Temperature Gauge: The gauge on your dashboard may behave erratically, jumping to hot, staying on cold, or not moving at all.
- Black Smoke from Exhaust: An overly rich fuel mixture, caused by a false 'cold' signal, can result in unburned fuel exiting through the exhaust as black smoke.
- Hard Starting: Especially when the engine is warm, a bad sensor can make starting difficult because the ECU is using the wrong fuel and timing parameters.
Known Issues and TSBs
For the 2013-2022 S8, several Technical Service Bulletins (TSBs) relate to the cooling system. TSB 2062951/2 addresses the cylinder head temperature sensor (G407), where a damaged O-ring can cause moisture intrusion and sensor failure, leading to a red coolant warning and various DTCs. TSB 2069248/1, for 2020-2021 models, points to issues with the map-controlled thermostat that can cause a red coolant warning even when the engine isn't overheating, triggering DTC P218100. 🎬 See how to replace the thermostat and refill the coolant. While not a sensor recall, NHTSA recall 16V-619 for some earlier models involved a coolant valve that could leak into the wiring harness and damage the ECU, which could present similar symptoms.
Choosing the Right Aftermarket Sensor
For a high-performance vehicle like the Audi S8, sensor accuracy is paramount. While an OEM sensor is always a safe bet, several reputable aftermarket brands offer reliable alternatives that meet or exceed OEM specifications. For critical electronic components on an Audi, it's generally recommended to stick with brands known for supplying European automakers or those with a strong reputation for quality control.
| Brand Tier | Brands | General Assessment |
|---|---|---|
| OEM Supplier / Premium Aftermarket | Hella, Vemo, Delphi, NGK, Bosch | These brands are often original equipment suppliers to VAG (Volkswagen/Audi Group) or are highly regarded for their quality and reliability in European applications. Choosing from this tier is the safest aftermarket option. |
| Reputable Aftermarket | Beck Arnley, Standard Ignition (SMP), Holstein | These are well-known aftermarket brands that produce a wide range of parts. They generally offer good quality and are a solid mid-range choice. Beck/Arnley is noted to work well by some users. |
| Standard / Economy | Four Seasons, Global Parts, Motorad, True Tech, VNE | These brands often provide a cost-effective solution. While functional, for a critical sensor on a complex engine like the S8's 4.0T, it's often worth investing in a premium brand to ensure long-term reliability and precise performance. |
A Note on S8 Engine Complexity
The 4.0T V8 engine in your S8 has multiple coolant temperature sensors. The most common one to fail is the cylinder head temperature sensor, often referred to as G62 or G407. A forum user on a D4 S8 located this sensor on the front of the passenger-side cylinder head. Always verify the correct part number and location for your specific model year before ordering.
Cost Comparison for S8 Coolant Temperature Sensor
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket | $13.18 - $45.77 |
| New OEM | $50 - $90 |
| Shop Labor | $100 - $250 |
Note: Costs are estimates and can vary based on location, supplier, and the specific sensor required.
Frequently Asked Questions
How many coolant temperature sensors does my S8 have?
The 4.0T engine has a complex cooling system with multiple sensors. Key sensors include the Engine Coolant Temperature Sensor (G62) at the cylinder head and the Engine Coolant Temperature Sensor on Radiator Outlet (G83). There may be others depending on the specific model year and configuration. It's crucial to diagnose the correct failing sensor.
🎬 Watch a professional diagnose P0128 and replace the thermostat sensor.Is replacing the coolant sensor a DIY job?
For a moderately skilled DIYer, yes. On the D4 S8, the main sensor is reportedly accessible on the front of the passenger-side cylinder head after removing some intake components. 🎬 Watch this walkthrough for replacing the A8 coolant temperature sensor. You will need basic tools and a deep socket. Be prepared for some coolant to spill, and have new coolant on hand to top off the system.
What happens if I ignore a bad coolant temp sensor?
Ignoring it can lead to serious problems. At best, you'll suffer from poor fuel economy and performance. At worst, the engine could overheat without warning, potentially causing catastrophic damage like a warped cylinder head. A faulty signal can also lead to excessive carbon buildup from running too rich.
Should I use thread sealant on the new sensor?
Check the instructions with your new sensor. Many modern sensors come with a pre-applied sealant on the threads or use an O-ring to seal. If it uses an O-ring, do not apply sealant; simply ensure the O-ring is new and properly lubricated with a bit of coolant before installation.
Helpful Videos
Technical Specifications
OEM Part Numbers: 079919523H 06A919501A 059919501A
The primary sensor is a thermistor type, typically with a 2-pin or 4-pin connector, held in place by a clip or threaded into the engine block/coolant housing. The 4.0T engine uses multiple sensors, including G62 and G83, for comprehensive thermal management.
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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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