heater temperature problem?

hello all, my cabin heater runs what I would say .....'warm but not hot'....a nice pleasant temperature but by no means 'hot'
the temperature guage always reads 80' and never moves, radiator never loses water and has the aproriate 'green liquid' inside.
is this normal or is my car just getting a bit old? it,s a 1975 model but is a 1 owner, handed to me by my father.
perhaps i,m just used to the 'blowtorch' of the modern day models.
is there anything or areas of the heating system i should check or possibly replace?
thanking you...in anticipation

Could be as simple as a small valve that fails, forget the name. More complicated problem could be an electrical control problem which could run several hundred problems.

I get good heat when fan is in LO mode, but no heat when in HI mode.

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'89 420 SEL
'90 300 SEL
'84 300 SD (sold it)