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Old 07-31-2003, 08:54 AM
JimSmith JimSmith is offline
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596
I believe the design temperature for normal operation of the car is closer to the 86*C figure than the present 96*C figure. When you are running with "excess" cooling capacity the engine temperature is regulated entirely by the thermostat. If, under those conditions the water temperature is 86*C, then that is what was intended for the engine coolant temperature.

When the heat load under other conditions exceeds the capacity of the system these fans come into play. This is normally not an issue as at highway speeds the air flow through the radiator without the fan should be enough to keep the system in the thermostat's regulation range. When you stop and idle in traffic, the fans are needed to regain some heat rejection capacity lost by the lack of air flow over the radiator surfaces. A higher water temperature will increase the effectiveness of the radiator as well, so the temperature stabilizes at a higher value.

If you have heating issues at speed, the thermostat is more likely the problem, assuming the fluid levels are correct. But an engine running with the coolant temperature being regulated by the thermostat is what was intended, and if the thermostat does that at 86*C I would not classify that as cold. I would call the 96*C value "hot" and, by the words in the manual, I would not consider it too hot. But I would be more comfortable with the 86*C number.

Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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