My wife has a 2005 Forester that had a problem with overheating. It has had new head gaskets, thermostat, radiator & hoses done at a reputable shop. It no longer overheats but the temperature increases on the gauge when she goes up long hills. It does not go out of normal range but she insist that something is wrong and is going to get another vehicle {never have another Subaru}. It has close to 200,000 miles and runs great. The cruise light flashes and check engine light are on. Scan shows catalytic converter. Could the Catalytic Convertor be causing the rise in temperature or is this normal and she just didn't notice before? Thanks

Check your electric fans.  If even one quits they will start to heat on a hill.    In driveway, hood open turn the a/c on , blower motor running.    Both your electric fans should come on .If not check fuses.   Wife's car did this... was a blown fuse on secondary fan.

Both Fans are working and fan relays have been replaced.

Well , Too bad...would have been an easy cheap fix. I then suspect you may need a radiator. 

It has a brand new radiator, cap, thermostat, and head gaskets

Could the catalytic converter cause a temperature rise. It is not overheating, just going up {in the safe range} while going uphill.

I have seen catalytic's glow red from too much fuel,  car hardly runs at that point.  However it had no effect on the temperature.   2005 is 13 years old now ... radiators do not last forever...   they are also easy to change and not that expensive to buy.   (EDIT)  My bad just reread your post you have a new rad.   ....  subaru thermostat ? or aftermarket ?

Edited February 6, 20188 yr by montana tom

Bypass the heater core and test drive it under the same conditions.

was an OEM thermostat used?

 

could there be a lot of debris/bugs built-up between the condenser and radiator?