I have yet to be able to try some of these suggestions. I am waiting until the weekend when I will be able to work on the vehicle during daylight hours (It is dark when I leave for work in the morning and getting dark when I get back home in the evening). I do know that their is circulation; I can see it when the truck is running and the radiator cap is off. I had very warm air (not hot, but definitely warm–about 100 degrees F according to a thermometer I placed in a vent) for a few days earlier this week. That occurred after letting the vehicle run with the radiator cap off on level ground, but I ran it only for a couple of minutes. This morning, I was back to having only cool to luke-warm air.