i have a 2004 outback 3.0 that started overheating 3 days after i purchased it. I had the obveous replaced; heat sensor. radiater cap. When I went to rewplace the thermostate I found that it had been removed. Put in an after market therm and it didn;t change situation. I replaced water pump. That didn't work. Situation now is that the two upper hoses get hot quickly and are under pressure; lower hose is much cooler and not pressureized.Logic dictates either a bad therm (but it overheated even when the therm was removed) or a bad radiator (but the radiator seemed to pass water freely when I had it out. I understand there is a chemical that detects carbon in cooling system. Seems that should be my next step to rule out hg. I also understand that heater plays a roll in cooling system but not sure how much it would effect water temp and pressure. Any suggestions would be appreciated

Subaru's, I understand, use a special oversized thermostat, so, using the aftermarket unit was probably a mistake. Cooling is a big part of the car, and I would not advise fooling around with this, otherwise, you could overheat and blow the head gaskets. That would be VERY expensive.

Removing or cutting out the center of a thermostat in a Subaru is an old dealer trick. The car will then run cold and not overheat. If you put in a regular thermostat, the car will be fine on local drives but overheat on the highway. That is because the heater core is blocked. With that year Outback, the entire cooling system runs through the heater core. If the core is somewhat blocked, the whole system is blocked. Will get little or no heat through the heater inside the car. Solution. 1. Bypass the heater core completely by re-routing the tubes. No heat in winter. 2. Put in a special H bypass where the water can still flow through the heater core but can also bypass the core and circulate back to the radiator. A little heat in winter. 3. Replace the heater core. OEM part costs about $80. But ... you have to remove the whole dashboard. It’s about a 5 hour job.