Taking it easy for the first couple of miles is better I've heard, it brings all the fluids, instead of just the motor oil and coolant to the right operating temp before you slam it.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).