lxman1

Perhaps you got a bad radiator. Mine did the same thing and replacing the radiator cured it. At highway speeds, you don't even need a fan, so I would doubt that it is the problem. Also check the lower hose to make sure it isn't sucking together at higher rpms.

g3mustang

At what temp do you check the lower radiator hose??

AdderMk2

Its the radiator.

The fan will keep the car cool at idle because it's not generating much heat.
when the car is under load, and moving... the air that gets forced through the radiator moves SIGNIFICANTLY faster than the air through the fan. If your car wont cool at highway speeds... its because of your radiator.

Check it for cold spots, and make sure you are running the proper mix of water/coolant.

g3mustang

ok guys thanks for the help!! i have a autometer temp gauge located in the factory temp sensor location. i have a 180 t-stat but looking at my temp gauge the temp doesnt start to go down untill 190 is that normal??

AdderMk2

yes...

g3mustang

ok last comment about this wnet to the drag strip and during a pass the temp doesnt go anywhere. only happens when im cruising. does this change anything??

AdderMk2

nope... still say its your radiator

g3mustang

Damit!! lol i found an old post with the same situation and you and mj said it was the waterpump or radiator cap thats where i got the idea from no biggie

AdderMk2

you would know if it was the radiator cap, because the cooling system would not hold pressure, and your overflow bottle would be full all the time.

If it was the waterpump, you'd overheat at idle.

g3mustang

so for fun yesterday i drained all my coolant. filled it back up waited for the car to get warm to burp the system, but the temp just kept rising. so i shut down the car at 200 degrees felt the top hose nothing was in it. popped it off to make sure. went to the autoparts store put in a new t-state car runs perfect. thanks for the help