My 90 Accord Is Overheating On The Freeway. When I Turn The Heat On It Blows Hot, And Then Temp Comes Down... Temp Gauge Reaches Almost To The Hot.... Seems To Do Ok In Town And Short Trips... But 30min Or More At 60mph Seems To Be Where My Problems Start. --- Water Level Seems To Be Ok... I Also Noticed That The Upper Hose Is Hot, Where The Lower Going To The Back Of The Engine Is Cool.... Could This Mean Themostate?