After not having my car driven in over a month because it's been in the body shop for a new front end conversion (06 to 05). What I've done so far as far as troubleshooting and what I have as far as cooling.

New Mishimoto Radiator.
New A/C condenser
Subaru Super Long Life Coolant (2 Gallons)
Attempted to burp the air out of the system.
Temperature gauge fluctuates from hot to normal then back to hot. (it gets confusing..)
Noticed that maybe because of the high performance radiator, it might need more than 2 gallons of coolant because OEM radiators call for 2 gallons already.
Overflow reservoir seems to be extremely low, but wasn't sure if that could contribute to overheating because the level on the radiator itself seems to be perfectly full.
Lower hose is cold, upper is hot.
New upper and lower hoses, and no leaks.
Heater on full blast gets very hot when temp gauge goes up.

I'm hoping that it's something as simple as just adding more coolant into the reservoir because im wondering if because its so low, the overflow pipe sucks in air instead of more fluid. Causing air pockets in the radiator. I need to buy more coolant, but Subaru is closed in the weekends...

I'm also wondering if it could be the thermostat. Considering that the oem radiator was probably off the car, rust and debris could have built up causing it to shut close..

Any other expert opinions out there would be good. Im confused as hell.

 

if your getting temperature spikes then that means there is air in the system. You said you got a aftermarket radiator, yes these do take more coolant then the stock system. about a half gallon more then the stock system takes. Stock says 2 gallons, I'd buy three gallons and have almost a half gallon left when I did mine. If your replacing all the hoses it wouldn't hurt to do a thermostat too, I mean while your there you know.

quick way to fill your system rather than filling the overflow up by the radiator is to pop the cap on the upper reservoir, the one up by the intake manifold and fill from there once the car has cooled down that is. Makes filling the system alot faster. then make sure your overflow bottle is at the full line.

 

Cool thanks! And refilling the reservoir by the turbo did help too. I should've done that first before changing my thermostat to troubleshoot. I ended up buying Kragen's thermostat made by Murray Plus. I figured i'd buy that first to see if brand really matters since i needed the car up and running. My car runs VERY cool (yet normal) with the new radiator and fluid and it feels good. Later i figured i'd do the boiling water test to see if the old OEM t-stat was bad anyway, which im assuming it is since it didnt open up.

SO for anyone with overheating problems, i suggest you cool down the car, check if fluid levels are full (upper reservoir by the turbo, lower resv. by the radiator, and radiator itself) of course burping the system during the process making sure theres no leaks. Then if that fails, thermostat change would be a good next step to do. Then after you can start to conclude to bigger things such as a bad radiator, or even a water pump and hopefully not a blown gasket.. which would be pretty obvious as plenty white smoke will come out of the exhaust. Well Thanks guys of i-club.