here is a little light reading on the LS cooling system for you to peruse through. the thermostat controls the coolant returning to the block, not leaving the engine like a lot of us are used to. it is a good idea to ensure you have some flow through the heater hoses so the thermostat reads the engine temp better. some have had issues with engine overheating or at least getting really hot and they have found this to be the issue. there are also steam lines to get rid of the steam generated in the cyl head area.
anyway, you probably already know that. this is still some good info though. lots of other stuff on this site as well, including a pretty good write up on the LS engine lineage.
https://www.pirate4x4.com/tech/billa...CoolingSystems