A mechanical seal for sealing a fluid in a space between an equipment housing and a rotatable equipment shaft, comprising: a shaft sleeve mountable on the rotatable shaft so as to be rotatable in unison with the shaft about a shaft axis, said shaft sleeve having a respective support surface oriented transverse to the shaft axis so as to face axially; a seal gland mountable to the equipment housing so as to define an annular chamber defined radially between said shaft sleeve and said gland, said gland having a respective support surface oriented transverse to the shaft axis in axially spaced opposing relation with said support surface of said shaft sleeve; a first seal ring (31, 51) mounted on said shaft sleeve for rotation therewith and having a planar front sealing surface (33, 53) and a back ring surface respectively facing said support surface of said shaft sleeve; a second seal ring (32, 52) non-rotatably mounted on said gland which is substantially coaxial with said first seal ring (31, 51) and has a back ring surface respectively facing said support surface of said gland, said second seal ring (32, 52) having a planar front sealing surface ((34, 54) disposed in facing, sealing relation with said front sealing surface (33, 53) of said first seal ring (31, 51) to sealingly separate first and second regions of said annular chamber during relative rotation of said first (31, 51) and second seal rings (32, 52) during shaft rotation; said first (31, 51) and second (32, 52) seal rings being formed of disparate seal ring materials having disparate thermal conductivities, characterized in that a thermally conductive one of said first (31, 51) and second (32, 52) seal rings is thermally conductive and has a greater thermal conductivity than the other of said first (31, 51) and second (32, 52) seal rings, said thermally conductive seal ring having a thin thermally conductive intermediate sheet (90, 91) fitted between said thermally conductive seal ring (31, 51) and its respective support surface, said respective support surface being defined by a thermally conductive material wherein a heat dissipating flow path from said thermally conductive seal ring (31, 51), through said intermediate sheet (90, 91), and to said respective support surface is thermally conductive such that heat buildup between said front sealing surfaces (33, 34, 53, 54) during shaft rotation is drawn from said front sealing surfaces (33, 34, 53, 54), through said thermally conductive seal ring (31, 51) and said intermediate sheet (90, 91) to said respective support surface and is dissipated therefrom. a shaft sleeve mountable on the rotatable shaft so as to be rotatable in unison with the shaft about a shaft axis, said shaft sleeve having a respective support surface oriented transverse to the shaft axis so as to face axially; a seal gland mountable to the equipment housing so as to define an annular chamber defined radially between said shaft sleeve and said gland, said gland having a respective support surface oriented transverse to the shaft axis in axially spaced opposing relation with said support surface of said shaft sleeve; a first seal ring (31, 51) mounted on said shaft sleeve for rotation therewith and having a planar front sealing surface (33, 53) and a back ring surface respectively facing said support surface of said shaft sleeve; a second seal ring (32, 52) non-rotatably mounted on said gland which is substantially coaxial with said first seal ring (31, 51) and has a back ring surface respectively facing said support surface of said gland, said second seal ring (32, 52) having a planar front sealing surface ((34, 54) disposed in facing, sealing relation with said front sealing surface (33, 53) of said first seal ring (31, 51) to sealingly separate first and second regions of said annular chamber during relative rotation of said first (31, 51) and second seal rings (32, 52) during shaft rotation; said first (31, 51) and second (32, 52) seal rings being formed of disparate seal ring materials having disparate thermal conductivities, characterized in that a thermally conductive one of said first (31, 51) and second (32, 52) seal rings is thermally conductive and has a greater thermal conductivity than the other of said first (31, 51) and second (32, 52) seal rings, said thermally conductive seal ring having a thin thermally conductive intermediate sheet (90, 91) fitted between said thermally conductive seal ring (31, 51) and its respective support surface, said respective support surface being defined by a thermally conductive material wherein a heat dissipating flow path from said thermally conductive seal ring (31, 51), through said intermediate sheet (90, 91), and to said respective support surface is thermally conductive such that heat buildup between said front sealing surfaces (33, 34, 53, 54) during shaft rotation is drawn from said front sealing surfaces (33, 34, 53, 54), through said thermally conductive seal ring (31, 51) and said intermediate sheet (90, 91) to said respective support surface and is dissipated therefrom.