Ok so I understand that when the engine reaches operating temperature that the thermostat opens and allows the coolant to flow.

What my question is that i would like to know what other parts engage/have coolant run through them when the engines reaches that temperature. Im trying to troubleshoot a sound i hear only after the engine reaches the right temp and the coolant starts to flow. Its a rattling sound btw. Any help/suggestions are appreciated.

 

Nothing else engages but the coolant flows through the engine and heater core and radiator and back to the water pump.

Does the rattling sound change with rpms or bumps ect? Some possibilities is a engine pulley to heat shields ect.

 

The sound does not change when I increase the RPMs. But I do know that the Cat on my truck is gone and I have a replacement already waiting for installation. I know that my cat is the source of a rattle in my truck but I just find it very odd that when my truck reachs its standard temp that the sound gets louder. So my next thought was that something that is connected to my coolants route could also be contributing to the sound.