Hello
I noticed when I first bought this slightly neglected RL with 130K the heat was very lukewarm when set at 80F on auto (climate control). The shop that repaired other issues also changed the thermostat and water pump when I told them of this. I found the air blowing was weak so I changed the really clogged cabin air filter (original). The AC was cold in the summer but this fall the heat blows warmer but only when I keep it at 90F and the blower speed on manual at the lower speed ranges. I am wondering would a simple coolant flush cure this or will it need chemicals to clean out the heater core or even a heater core replacement or something else. Looking in the coolant I see small glitter in suspension in the coolant (stop leak?) and grey gunk would form on the underside of the cap, before some coolant would get out of the cap (worn gasket/gunk buildup) but I replaced that and haven't had any problems.