I recently picked up a 94 NAS 90. It's seems to be running pretty good but is losing coolant with no obvious leaks in the system. At highway speeds, it runs a little hotter than I'd expect but nothing too alarming. At idle or slower speeds, everything seems to stay in check on temperature. I'm guessing that I'm either losing coolant through a bad head gasket or it's escaping the expansion tank via a bad cap when it gets hot. Any other common places or things to check? Thanks for any suggestions.