It could also be an "intermittant" pump like I had. Ran at idle, ran with the car off just not when driving. Put in a new pump and boom back to normal.

 

But you did see the coolant flow threw did you? And what fuse is it

 

I saw the coolant flowing, I felt the coolant flowing but it just wasn't working one bit. Cruising IAT2 130+. Now they are 10-15* above IAT1.

Not sure on the fuse..

 

Ok, do this:

Get some wire and two MALE connectors. Cut the connectors in half (you'll see what i mean in the photos).

Make this:



Find this relay: (this is for a Red Line, not sure where the Cobalt ones are, sorry. This method may not work for you guys, but I'm not sure so I'm posting it anyway.



Jump it like so:



The relay may be in a different spot on the Cobalt, but I'm sure you can use the same idea.

Once the key is in ACC mode, you should hear the pump run if it's working. My old one used to run, but like ****. I'd hit it with a hammer while it was running and it would pick up RPM. It would then slow back down. I eventually replaced it.