Starting this thread on Heater Core sludge ...since the search is apparently having problems... ( index passatworld_com-threadindex,passatworld_com-threadindex-delta: no such filter attribute 'replycount' ).
For those of you who've flushed heater cores, what did the "sludge" look like? If you've had an oil/water cooler failure that allowed oil into coolant, indicate this as well. (Is this the cause of sludge?)
Specifically looking for instances where the heater core formed sludge without ony other apparent failure. Could it be that the metal used to manufacture the HC is causing a slow fouling (sludge build-up on metal surface) regardless of the coolant used?
Thanks for your responses/opinions.