On LT4, probably same on many others.
Did you ever wonder what that black plastic thingie was connecting the two lengths of the heater inlet hose?
I was replace ing my hoses and couldn't figure out what it was so looked it up as the USPTO by the patent number 4800925.
It's a flow control valve to cut dowm on heater erosion from high flow rates at high rpm. It lets them size things to run a lot of coolant through the heater at low speeds without being too hard on the heater at high speeds.
That's your trivia lesson for today, you are now being returned to your regular programming.
While looking for that tidbit, I found out that if you type the patent nember and the word patent into Google, it asks you if you want to see the patent at the USPTO