'92 f150 overheat

I have a 1992 Ford F150 nite stepside, with the 302 5-litre engine. The engine keeps wanting to over heat. Replaced water pump, upper and lower hoses, thermostat and had the dealer mechanics check the system. They can't
figure it out. They can not find a blockage in the radiator but thats not saying much. By now you ask what are the symptoms? Well, let me tell ya.. First time noticed the truck overheat was on a short..less then 10 miles trip on highway and off never faster then 65 mph. When got home noticed gage just at the high mark. Shortly after turning off truck radiator fluid overflowed out of the resevoir. Since then I am able to keep the temp by the 'm' on the temp gauge. Also, checked the fluid and no indication of a blown gasket, no leaks ect... the dealer even checked the fluid for a blown head gasket. Not sure what to do from here.
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mjb wrote:

Does it overheat on the highway, or just around town? If only at low speeds, fan. All around could be condensor blockage, engine timing, incorrect coolant mix, bad temp sensor or gauge (may be ground connection).
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Please explain how a bad temp sensor or gauge causes water to come out of the overflow? If it has a good cap and the system holds pressure it's overheating.
Still need to know if you drive it in town will it overheat or not?
Al
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