The question is what are they for, if not the temp? And more importantly HOW DO YOU KNOW when the temp is safe to drive hard?

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BMW - X5 4.8i w/all US options packages, 19" Y wheels, White/Tobacco, Huper Optik 50% tint
Mercedes Benz - E320 CDI Park Assist, NAV, Folding Mirrors, Premium Sound, Voice Command, Sunroof, Auto Rear Shade, Bi-Xenon