So, I'am having this problem still with my poor mustang. My high hose is hot, but my low hose is cold. Does that means my Thermostat is put on backwards, and yes, I replace tha RAD. ! Thanks!

Also, is it good to use a failsafe thermostat with high temp. like 180 to 190?

 

When the engine is COLD, open the rad cap then start the car. Watch to see if water starts flowing thru the inside of the rad, Be careful to put the cap back on pretty soon though or water can start boiling out of the hole.

 

If the stat was backwards, you wouldn't be warming up your upper hose. After the engine is hot, your lower hose will warm up. 'til then, your radiator is doing its job.