99 Taurus Overheating

I have a 1999 Taurus with a 3.0 Vulcan that only over-heats at freeway speeds. Local town driving or at stop lights idling works great but once you get to 50+ miles and try to pass someone, it will jump from half way between H & C to Hot and overheat spewing fluid. I can drive it for a couple of hours in town stop and go but 30+ minutes at freeway speeds and it will overheat. I have flushed system, replaced radiator, heater core, thermostat,water pump, hoses. Electric cooling fans seem to work fine. Wierd at highway speeds cooling fans don't really come into play. Seems like water pump is not keeping up at highway speeds but it's been replaced 2x now. I have been told these years have an internal engine rust problem but the fluid is pretty clear after flushing. Any suggestions.... Much appreciated!
Jeff

When the thermostat was replaced, did you notice (if you did it yourself) if it has a little jiggle valve? That valve needs to be oriented properly at the 12 o'clock position. Also, I'm not sure if the thermostat will only physically fit one way, but you'd want to be sure it is not in backwards. Of course I'd expect that issue would show up during city driving as well.

Also make sure there is no air in the system. If your thermostat does not have the jiggle valve, there is probably an air bleed screw in the cooling system somewhere.

You may also want to try replacing the cooling system pressure cap with an original equipment cap. The system relies on the proper pressure for boil over protection (a pressurized system raises the boiling point and freezing point). Some forum users have experienced poor luck with generic pressure caps and have ended up purchasing a Ford cap to solve their issues.

In the past, there were issues with some waterpumps having reverse impellers. Depending on the belt routing, some pumps would rotate one direction and on other cars the pump was intended to go the other direction. If you didn't verify when the pump was replaced, hopefully you still have the original waterpump and can compare the impeller direction. If you don't have the original pump, pay attention to which direction the belt would have the pump rotating and see if that makes sense with the way the impeller is intended to work.

-Rod

Rod,
Sorry, forgot to mention but I had also replaced the bottle and cap with original ford parts. Yes, I'm sure the thermo is in correctly but didn't notice the jiggle valve? Impeller is moving in correct direction per belt routing as well. As you might notice, I'm running out of things to check. Like I said, you can be doing 60 mph but if you punch it into passing gear, it will start to overheat. Keep it at 60 and it's fine. I have also read that somewhere around 62-65mph the PCM will shut off the cooling fans but the fans shouldn't be needed at those speeds anyway. Any other ideas?

Wild shot.
Has your gas mileage dropped? A drop would indicate that the timing is retarding.

Had it into the Dealer and he ran overall diagnostics and computer for codes, none found . I'm assuming timing was checked as well but mileage hasn't changed and runs perfect other than overheating problem.

Since you've replaced the radiator, it shouldn't be restricted, but you may want to check the A/C condensor for debris that may be restricting air flow. Maybe, just maybe, the cooling fans pull enough air around the condensor, but when on the highway, if the fans shut off (I'm not sure about that) the flow may drop. Yep, it's a long shot.

After you pass someone on the highway, will the temp begin to drop again once you get around the car and start to slow down/let the tranny go back in to overdrive?

Does the car have a separate transmission cooler, or is the tranny cooler built into the radiator end tanks? I'd be frightened if the tranny fluid was getting so warm that it was actually heating up the coolant that quickly, but just exploring the options.

-Rod

A/C Condensor seems to be very clean. Tranny lines are cooled by radiator but they are hot but not burning hot to the touch when car is hot.

Yes, once you pass, if you ease off the accelerator it will come back down to normal temperature. This is a funny one...