2021 Audi S4 Problems: 1 Issues Every Owner Should Know
2021 model year · 107+ owner reports · Updated April 2026
According to Au7o's analysis of 107+ owner reports, the 2021 Audi S4 has 1 documented known issues. No issues are rated critical, indicating generally reliable ownership. The most commonly reported issue is Thermostat Housing Failure and Coolant Leak with 107 owner reports. Across all issues, repair costs range from $300 to $800. DIY maintenance guides at au7o.io.
All 1 Known Issues
On the 2010-2025 Audi S4 3.0T, the plastic thermostat housing on the S4 3.0T is prone to cracking and leaking coolant. The housing sits at the rear of the engine making leaks hard to spot until coolant loss is significant.
Common Symptoms
- Coolant loss without visible leak
- Overheating warning
- Sweet smell from engine bay
- Coolant puddle under rear of engine
- Temperature gauge fluctuation
- Low coolant warning
How to Fix
Replace thermostat housing assembly with updated part. Use OEM or quality aftermarket housing with metal reinforcement.
What Owners Are Using
Parts and tips from 107+ owners who fixed this issue
- UpgradeThermostat Assembly (Wahler #410671.103D)