I have a 1998 Mustang GT ...I'm not sure what the problem is but if I'm driving on I95 for about 20min+ at around 90mph my add coolant light comes on, well I check the overflow res. and its full I've checked when its hot and when its cold, its full so i don't understand why I'm getting this light but its only when I'm on the highway and the car is hot for 20+ mins. A couple months ago i flushed out the radiator myself and ran a house through the block to get all the old **** coolant out and replaced the thermostat as well and refilled it back up with Preston concentrated coolant and distilled water. It runs fine and never get that light unless I'm on 95. Any advice or suggestions?

 

Common issue, don't sweat it https://mustangforums.com/forum/4-6l...ml#post5936191

 

so after reading that, it seems that its just a faulty sensor because I'm not leaking any coolant any where so I know my crossover isn't cracked

 

correct!

 

I just unplugged mine. Stupid thing isn't even worth changing. I've got an alum x-over, and it always stays full. I'll just watch my temp instead.