Join Date: Feb 2004
Location: Lexington, Kentucky USA
Gepetto, why not try burping the system to allow any air pockets to vent? It sounds like either a circulation issue or air in the system, which could be inter-related. At higher speeds, yes you are shoving more air through the radiator but there is also more friction and heat generation than at idle. And that heat has to be dissipated or it will increase coolant temps. Do you reckon the water pump impeller is still attached to the shaft? I have seen impellers come loose and freewheel.
And I would not rule out a bad thermostat, either.
Lexington, KY USA