I'm not sure about a rattle, but if you look at the bottom of it, you can see the ball or the hole where it used to be if you completely remove the gasket. The ball missing will not make it not reach operating temperature. I've driven mine into a 25-30 MPH wind with outside temperatures right around 0*. I have no ball in the thermostat housing and never put cardboard in front of my radiator. Not only did I have plenty of heat from the heater with it not on full blast, my mechanical temp gauge stayed right below 195*. If something was not letting the thermostat close completely, I can see where it may never reach operating temperature. When I bought my current truck, I thought the heater didn't work unless it was about 45* or so outside. I thought core was plugged until I found out that neither heater hose was even warm with the engine running, the heater on high, and after driving 15 miles. When I went to replace the thermostat, there was a piece of broken 6.9 style glow plug controller holding it open.