Having heater issues with my 91 560SEL. The heat takes very long to get really hot when the car is at operating temperature but most of the time just cool to luke warm air blows through the vents. I had recently changed the coolant been probably 2 years already with the xerex yellow. I am leaning either towards the monovalve or aux waterpump? Any suggestions would be great.

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6