Originally Posted by somewhereinusa
Are you sure that diagram is correct, it's not how mine was plumbed. It also doesn't make sense. The water is going to take the path of least resistance meaning, the loop to the rear heater. What inducement would it have to go into the front heater unless, it has an extra pump there? I had an extra pump but, it was also in the loop to circulate water better the front. (engine in the rear)
It's definitely worth opening the main heater access and taking a look because not all buses are plumbed the same way. Mine was exactly as I described it in my first diagram (which I'll add again at the bottom of this post) with no extra pump. When both heater cores were in place and connected there was no path of least resistance. That is, both heater cores were about the same size and imparted the same level of fluid resistance. In my situation, taking the rear heater core out and creating a loop would have created a significantly easier flow path and thus would reduce the flow going through the main heater core.
Perhaps this ugly diagram will help explain what I'm saying:
In that diagram if you want all of the flow to go through the bends (heater core), you should not create a path with very low resistance. This is what I did. I would urge people to take a look at their heater before looping since it could seriously reduce the heat output of the main heater which also provides defrost.