overheating shutting down on 1994 Ford Mustang

in two weeks mustang gauge showing rapid change in overheating then cooling down on its own. I've changed thermostat and heat regulator. car runs fine over 50 miles but then I exit in a town and engine shuts down overheating, yet temp gauge only shows half that its overheating, after cool down car runs fine again. I've yet to flush out cooling systom as my next step.

by in Las Cruces, NM on June 12, 2011
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2 answers 2 comments
ANSWER by , June 12, 2011
Check the operation of your cooling fan, it may not be working properly, that may be why it runs cooler on the freeway. Also check for any service engine soon codes, you may have a defective coolant temperature sensor or gauge sensing unit. here are some shops if you need some help: https://repairpal.com/directory?address=88001&car_brand_names=Ford
COMMENT by , June 13, 2011
the temperaure sensor I've replaced but not the gauge sensing unit. thanks for the help and will post of my outcome.
ANSWER by , June 12, 2011
Two other things to check: Rapid fluctuations in temperature readings could very well be caused by air trapped in the cooling system. Make sure that all air is bled from the radiator. Also, check that bugs or debris is not built up on the radiator or condensor restricting air flow through the radiator.
COMMENT by , June 13, 2011
ahhhh I've got a feeling that this may be the issue in how you've explained it....there are no leaks of anykind and everything else is working properly....so I assume I've got to just flush the entire cooling systom??