When it gets hot, it goes out the overflow and into the bulk head. That's what you are seening. make sure it doesn't have a bubble in the line around the rails and through the back cooler. it takes some work to get them out. Also, you might have to use scratchers in low snow conditions. The coolers on the Fusions rely too much on the rails, and there isn't much of a cooler in the front or the back, so i had that problem all the time on my 600 fusion. Might want to make sure the water pump is still working too. when the motor is still cool, have the cap off and you should be able to see the water flowing. if it isn't your water pump might be broken.
