Hello all! The heat in my 2008 Lacrosse CXL 3.8 has gone luke warm. I'd like to back flush the core with a flushing tee connector. What size hose is the outlet side? This should work? Hopefully?

 

Before getting involved in what may or may not be the problem, Do we know if the thermostat might be stuck open.

A quick way to tell, cold engine ,remove the radiator cap ,have someone start the engine and look into the radiator. If you see the coolant circulating with a cold engine, the thermostat is stuck open. If replacement is required, a 195 degree thermostat should be installed..