Try running a higher percentage of water to coolant. I run 75%/25% and a bottle of water wetter during the spring/summer and early fall. I also sometimes short shift just a bit. Try to keep it under 6k RPM, especially on 90+ days. A lot easier to do with a dct. I've never hit limp mode and I've run pretty hard. Even had the car co driven on a track day on a high 80s day. I want upgrade my oil cooler, but have a 2016 GTI that I'm modding also. Just not enough money
