Sandy Blackwell

I pulled a good one and need help. I was putting a new thermostat in my CL700 and as I took the off the part that the water filter is on out slipped a cylinder with a ball bearing at the end (Before I got a chance to look at it). I don't know which way it goes back. Does the ball bearing end go in first toward the radiator or the opposite. Obviously I don't know the names of these parts but can usually figure out how to do things...not this one.