My new bus,  a 90 automatic which sat for a few years seems to be makin coolant vanish. I checked it for leaks thoroughly before its commissioning and we addressed some problems.  Now I find myself filing the expansion bottle behind the license plate for the second time. The system holds pressure, I don't know of any leaks, the heads have a thousand miles on them, and the heaters produce heat. The temp gauge has always seemed to stay a little low but that may just be where this one likes to hang out. 

Any suggestions on where to start? I've been out of the wbxer game for a little while and my head still thinks engines are supposed to have simple and reliable cooling systems like my zetec. 

-craig
'85,'90,'87 Syncro