hellow everyone hope evry one has good thanks giving i have 83 td with 242000 miles problem is , the temp dial never gose beyond 80 i just drove 2000 miles last week and while comming back i drove straight 850miles from s.c. to chicago in 13 hr avarage about 65/hr idrove 80mph continuously except stopping for desiel with all this temp dial never went above 80 it was really cold and heater was not blowing real hot air even regulator was on max position in summer with air on temp dial never gose beyond 80 my question is is termostate is not good or there no thermostate at all ? or how heater cor is bad ?9 though it dose blow hot air but not enough hot for this winter cold any and every help would appreciated thanks chandra

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Your thermostat may not be getting the engine hot enough but 80deg C is plenty of engine temperature for good heating.

I would replace the mono valve capsule and verify the operation of the auxilary water pump.