New answers tagged subaru
From the above and your description I would change the coolant thermostat first, and secondly remove and check out the water pump for a displaced/broken impeller.
While a manual transmission in the Subarus seem to run high at highway speeds (according to this website, 3200 @ 70mph is normal ... this to me who runs a vehicle which maintains ~1800-2000rpm at 70mph seems high, but nothing like what you are experiencing), running over 3500rpm at 50mph seems quite a bit excessive. This could be the cause of your heating ...
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