Hey guys, I noticed my car was taking a very long time to warm up, so I decided to replace my thermostat assuming it was "stuck open". And I'm glad I did. I've attached 2 photos showing the old thermostat (left) and the new thermostat (right). As you can see there is some debris in the old thermostat. I assume that black debris is the remnants of a silicone valve that is supposed to cover those holes, much like an oil filter? I am surprised to see that valve deteriorate and break apart like...

When to replace thermostat?