...and flushed, and flushed the heater core. Seemed to have good flow in either direction. No large chunks came out, just rusty water/coolant and some sediment. All the hoses seem open and not leaking. I'm still thinking that it's the ACC amplifier because
1) it came out of my parts car so it's not new; 2) I opened the servo water valve by applying 12v and when I plugged it back in to the normal circuit it closed up again;
and 3) the aux water pump won't come on (unless I jump it to the battery)

So, I guess I'll buy a new amplifier and new temp sensors while I'm at it...

also, I have to replace the parking/emergency brake pads so the #*@% thing will pass safety inspection...will probably go ahead and do a complete rear-axle brake job while I'm in there.

__________________
1978 300SD 149K miles silver-blue "Maxine" (mine!)
1979 300SD 318K miles red "Helga" (SOLD)
1980 300SD 321K miles yellow "Linda" (younger daughter's)
1980 300SD 148K miles blue (SOLD)
1980 300SD 153K miles green(parts car, SOLD)
Yes, I have a W116 fetish :-)