I found a few threads on how to replace this part without buying the entire Heater hose Assembly, but I have yet to find in these forums or on the web a good explanation as to what purpose the plastic heater valve has? It seems to be a somewhat poorly made part, that can crack open over time and drain all your coolant leaving you stranded? If anyone knows exactly what part number #10188036 does I'd love to know. The only thing I can come up with is that is prevents backflow or possibly increases the pressure as the coolant flows through it?? when mine busted I was luckily only 1 mile from my house and I was able to drive home after the engine had cooled.

 

It is an apparent restrictor of some type. The actual part is called a flow control valve. I have a suspicion that it contributes to the heater core being easily clogged. It is possible that it was put there to reduce noise from coolant rushing through the heater core at high engine rpms. Just a guess.

[edit] There have been those that have removed the part and reported no problems that they noticed.

 

bond...
What you are describing is EXACTLY what happened to me last week! The cheap plastic tube broke into and dumped out all my coolant. I just removed the heater hose assembly and made a loop to bypass the heater core. Just make sure that you leave the bleeder section on.