the heater core in my 74 fj40 gets super hot (sounds right) on the bottome for the lower vents but the top of the core never gets hot - I can place my hand right on it. It there and air bubble or some junk stuck? New cruiser to me so I do not know how long it has been like this. Any ideas on diagnostics / solutions? I was going to isolate the core and use radiator flush on it / maybe take a hose and flood it out. Any other thoughts / plans? Thanks