From what I have read so far about the 87 300D's original head problems, is that it seems to be caused from either not using the proper antifreeze, or else not changing it frequently enough. The one I just bought has the correct antifreeze in it, but I don't know how old it is, so one of the first things I want to do is change the thermostat and flush out the system. My concern is how do I flush the system out, without causing scale and such to come off and potentially clog up the coolant passages? The head seems to be ok, I checked the oil (which hasn't been changed for 3 months) and it didn't show any contamination, and the exhaust is clear. The car did almost overheat on a test drive, but found the aux fan fuse had blown. So I want to do the coolant change the proper way to try and extend the life of this head.

__________________
87 300D - Running on Veggie oil; 260,000 plus miles; Original #14 head