No, I didn't have a heart attack! In an attempt to prevent the "AC Performance Mod" thread from going over 30 pages, I decided to start a new one for my ultimate solution. This is in the engine and drivetrain forum, because the engine is the primary beneficiary of the modifications. The whole concept combines several aspects of issues surrounding this type of mod. The subject got started in that A/C thread for the purpose of improving A/C performance, however there are a few more things related to coolant flow in the back of the block that did not get properly addressed, and could have implications for someone diddling around with the water jacket plugs and heater hoses.

The most obvious application to me was tapping the rearmost port on the head there for a coolant filter. This is a must-have mod IMHO, YMMV. Neither here nor there. If you like it, fine. If not, skip it.

Around the same time, I also became aware of an application for this coolant port involving an issue with high performance engines blowing freeze plugs. It seems enough rpm will cause your engine to exhibit this behavior due to increased pressure in the water jacket. Adding coolant flow out the top of the head there may mitigate the problem. Although I don't expect to ever invoke this issue turning some crazy rpm's, I figure it's covered now anyway. If that's all you are worried about you can get a $500 kit with a fancy regulator from Opie or Wicked Diesel.

Last and certainly not least, the rear portion of the engine has always suffered from the potential to overheat before the forward areas. This is just a fundamental limitation in a water cooled engine under certain circumstances. Normally it is no great danger depending on your application and environment, but the potential is there. Cummins has been selling kits in various forms to address this problem for hard working engines in commercial applications since way back when. So at the end of the day, there are lots of good reasons to do something like this.

Now here we have it, done my way. Both rear ports from the head's water jacket are now flowing coolant at all times, either through the filter and heater core, or through the filter and a heater core bypass:

http://stuff.is-a-geek.net/PhotoAlbu...ics/CRD_36.JPG
http://stuff.is-a-geek.net/PhotoAlbu...ics/CRD_37.JPG
http://stuff.is-a-geek.net/PhotoAlbu...ics/CRD_38.JPG

The heater core return is now basically a double-tee, accepting return flow from the filter and/or the core itself filter and a heater bypass line, depending on the valve position selected. Seems to work perfectly. With the heater on high, fast idling in the driveway, I can turn the bypass valve 90 degrees, go back into the cab, and with my hand in front of the vents, feel the heat disspate to nothing within a couple of minutes. I will probably go back and re-do the heater inlet hose barb to get it a little further away from the exhaust manifold, pointing straight rearward to the heater core inlet at some point. I only did it like that to utilize an existing bend in the factory hose. I don't relish the idea of replacing that hose, it's kinda hard to reach.

 

Where did you get those 3 way valves?