There is a question to be asked. What's wrong with running 90+C on the highway in the summer? I've had my 300SDL since new and it runs 86-90C in the winter and 90-95C in the summer w/o AC on the highway. Add AC and it runs 94-98 on the highway and about 100C in the city. Remember, the aux. fan only kicks in at 105 due to engine heat. (Kicks in sooner for the AC ) MB Engineers must know something. The 603 does run hotter than the 617, probably to reduce emissions. I did replace the fan clutch and the thermostat a couple of years ago, when it was running hot, esp. in city traffic. By the way, my (orig.) owners manual states that the temp will rise "near" the red mark sometimes when driving. Just DON'T let it get into the red portion of the gauge. And, my 18 year old car has a healthy original alum. head and burns 1/3 qt. of oil every 3000 miles - just like it did when it was new. (MB(only!) coolant replaced every 2-3 years. Roteller-T oil changed every 3000 miles.)

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback