Up here in the great white north... Well, its damp and green where I live...
I found that when driving the truck in cold weather, the heat riser valve doesn't just open when the manifold heats up. It opens and closes, depending on the temperature of the bimetallic spring right? I found that often, when pulling into stop and go traffic, where there were periods of idle, it would begin to heat the manifold again, if the temperature under the hood began to drop. Same thing when it was really windy. In fact, when windy and cold, sometimes it stayed on heat all the time.
I guess it depends on where you live, and what kind of driving you do. With a functioning heat riser valve, even if you live somewhere warm, you get a much faster warm up, with less stumble.
Plus, I always loved that after I shut the truck off and I was standing near it, I would hear the valve click back over to heat.
Just my two cents.
