My m104 seems to like right around 80, maybe a little more in traffic, up hills, with a/c, etc. Usually NOT up to 90.

I am curious what the optimum is. Should you start worrying if the car reads, oh 100 or 110 and holds there, considering the red zone is 120? (Barring the obvious fact that is usually doesn't read there so why is it now?)

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro