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I have an 70’s truck that is still overheating at highway speeds only. everthing has been replaced, but still runs a little hot. I am wondering if replacing the fan clutch with just a straight fan would cure the situation. Truck only gets 8 miles to the gallon now but with a 460 cid, I don’t think that running a straight fan all the time would affect the current mileage by much. Any thoughts?

Could you be a little more vague?

“70’s truck,” There were ten years in the 70’s. Not all F250s were the same.

“Everything has been replaced.” Everything? Really? Then you have a brand new 70’s F250, and it shouldn’t overheat.

Are you sure the temperature sender and the temperature gauge are giving you accurate readings? Have you measured the ACTUAL temperature of the coolant?

Sorry, 1975 f250 w/460cid. Engine rebuilt, radiator routed out (shop stated radiator like new), new 13 lb cap (per spec), new water pump, thermostat, coolant at 50/50, new reg fan clutch and then heavy duty fan clutch (heavy duty fan clutch did cause the temp to go somewhat loweer, so pretty sure temmp gage is within the ballpark), new sending unit, new hoses, may have missed something but everything is basically new. Timing according to spec at 10 BTC although it does run cooler at 14 btc. Does not overheat even when setting at long traffic lights and I live in Tucson, AZ. Only does it on the freeways at 50 mph or higher. The higher the speed, the higher the temp. Even slight inclines cause the temp to rise. Does have A/C condenser and trans radiator in front of the regular radiator. Wife has a 1967 f100. Straight fan and no shroud, it never overheats at anytime. Hence the question about going to a straight fan or flex fan on the 1975. At wits end. All suggestions gratefully accepted.

Just a few comments.

  1. A routed out radiator does not a new radiator make. Did they do a thermal mapping of the radiator before they routed it? After? You’ve changed everything else, have you considered a new radiator?

  2. has anyone checked out the tranny cooler and the AC evaporator (“radiator”)? If these are generating excessively hot areas that hot air hitting the engine’s radiator will compromise the ability of the radiator to dissipate heat.

  3. are all the shouds and air deflectors in place, including that plastic shroud beneath the front of most vehicles?