2010 Subaru Legacy 2.5

Markw1952?

Heads have been checked head gaskets are fine

Do the fans work? How did you check for a leaking head gasket?

BTW Mark has never turned a wrench in his life.

I thought he migrated away...or got lost in Priusville? Ed's right on it, except that the engine coolant temp function is in the ECM, so it's likely to be the fan switch or relay, or a fan itself. I'd also back-flush the rear heater hoses, as they are in-line with the system and can get blocked by additives and/or age. F_O_R: percolation in overflow vessel is easiest. Ern TSG/B

Hmmm...I suspect the wrench may not have plugged the fans in after the work? Happens.

Also verify that OE large-orifice t-stat is in place, as cheap aftermarket ones restrict flow.