I was reading the service manual and trying to better undestand the water valve and the damper lever on the heater core. How is the best way to check this? I have felt my hoses and the return hose is warm but not as hot as the supply line. I have luke warm air. So I know I am getting some flow which is good, but trying to see if it is my valve is not opening all the way open or a partial clog. any helps and pics of this check would be great. The diagrams are decent but actual pictures help out so much more. Thanks yall.

91 Montero LS "Sandstorm", Auto, Dual Bouncy Seats, 2" Suspension lift, 2" Body Lift, GENII front IFS, 32" MT tires

89 Raider "Trailbreaker", 3.0, Auto, Dual Bouncy Seats