Hey
I'm on aborad studies in California and bought myself a Ford Mustang a month ago for traveling. Since then i have some problems with the engine temperature.

The Problem is:
The Engine gets very cold when im driving on the freeway. As i know from other cars, the temperature needle should stay in the middle of the scale but it does not.

My Mechanic replaced a (damaged) Thermostat at first with an 180f Thermostat, later i let i replace with an 195f Thermostat. At City-driving the car reaches normal operating temperature... when i drive on the freeway the temperature falls down to almost "cool".

Do you have an idea whats happening?
I don't think the second new thermostat is damaged too...

Thank you for your help!
Lukas

 

Maybe an issue with the cooling fan running while car is at a higher speed. it should only come on when engine reaches a certain temp and if it is staying on could be your problem .

 

Sounds like fan running while car is on highway and not shutting off

Don't know much about 99 V6's but in general if it's a non electric, mechanical fan, that runs off the accessory drive belt the clutch may have failed on the fan itself. When it's hot the fan engaged and runs with the belt, when it's supposed to spin freely and the clutch so the accessory belt still turns but the fan doesn't.
If it's a mechanical fan this is the easiest of all fixes. You would need a replacement that you can get off of rock auto or a local parts store and it's like four bolts attached to the water pump pulley and you're done. After you loosen the belt first.

But make sure that's what it is first.

 

IT could be that the thermostat was installed upside down, which means, if the rpm go higher, the engine cools down. I had that issue with my Taurus. Especially on the freeway. You can notice that also during city driving if you go above 2500 for some time and see if the needle goes down. If it does, then it is upside down. I don't think it is the fan, as the thermostat should close, once the water is too cool. And then less water goes through the radiator...
LEXiiON

 

Are you sure you put in a higher temp thermostat? If you put in one that's too cool, it will keep cycling the radiator fluid constantly.