What is causing my 99 ford f150 to overheat while on the highway

First The heading says 99 Taurus but the question says 99 f-150. Second, are you saying that the engine is overheating? The heater won't work if the level of coolant is low and that would explain overheating. The thermostat controls the temp of the heat, so if it is stuck closed then water can't circulate to the heater and the vehicle would overheat, but this is unlikely.

the other answers seem to concentrate on a non-working heater. Good luck with this problem.

Could be a fan clutch, sticking thermostat, or restriction in the cooling system including air in the system.

Does it slowly overheat while driving down the highway..If so the radiator is probably clogged..It can be partially clogged and cause the car to overheat,,but usually takes a little while...If it overheats in traffic..(stop and go ),,but does fine going down the road,,then it make sure your fan is coming on..

is the cooling fan operating properly(on and off at proper temps),does the rad have a flow problem this can cause it as well.you don`t say when and how long it takes to overheat.sitting idling for long periods of time,driving in the city only,on the highway,coming off the highway,only on acceleration,only with the a/c on.all these factors can make a difference in finding the problem.have you told the shop when and how its overheating.you may have to drive it under the same situation to get it to over heat and take it to the dealer and have them check it out when its happening or take it to a shop as dealer techs won`t spend as much time on it as they should because they are paid flat rate and if nothing shows in short order they kick it out the door and move onto a paying job.

timing is off thats the only thing that would still cause bit to overheat if everythin g is new

needs new water pump

i have a grand voyager 1999 and it temputure is running on the 3quater mark on the gauge is this right....

When driving down highway only, it overheats? When running steady, I take it you mean, sitting idling? If it's only overheating at highway speeds, and all else has been checked out & is o.k., I'd take a close look at rad hoses for soft spots (easy to squeeze) that may be causing hoses to collapse at highway speeds & restricting flow of cooling system. Another thing to try is, turn your heater on high fan & high temperature when it starts to heat up & see if temperature gauge goes down (cooler) at all. If it does, then rad not doing it's job properly.

possibilities include: fan clutch, water pump going out, missing fan shroud or baffles in front end, clogged radiator fins or a/c condensor may need cleaned. Possibly stuck thermostat, low coolant level , and this can be caused by faulty radiator cap. Hope this helps!

you may have a stuck thermostat,if all fans are working then just flush out radiator and replace
thermostat.check for any coolant leaks and check coolant level after few days