We too have experienced intermittent overheating with our Cummins 400 in a 2008 Winnebago Ellipse (rear radiator). On three occasions (June, Aug, & Sep) the engine coolant temperature quickly rose from normal (179-189) to 230. Increasing engine speed made no difference, and in all three incidents we had to pull over and shut down the engine.
Once we restarted the engine (the last time within 2-3 minutes of shutting it down) the coolant temperature immediately returned to the normal range, after which it operated normally. The latest incident, just two days ago, the ambient temperature was in the fifties and we were on a relatively level stretch of interstate traveling at 55 mph. With the exception of these three incidents, the engine coolant temperature falls in the 179-189 range except for very hot days and/or significant grades (when it may go to 205 or so).
We spoke with Freightliner Customer Service and the tech suggested a faulty fan clutch. Does this seem possible? Many thanks to all for your insights.