I've always used Mobil 1 synthetic and usually mix 4qts. of 10w-30 with 2qts. of 15w-50 to thicken up the viscosity a little. I have a 1999 Jetta GLX (A3) VR6 and my oil temps run close around 242F in the summer with AC on when running 80-85mph on the highway. Are there any synthetic 5w-30 or 10w-30 oils which are naturally a "heavy" 30 weight or even approach a 40 weight? Thanks for any recommendations.