So I just recently replaced the timing belt, tensioner and idler pulleys, water pump and gasket, and OEM thermostat with new gasket. Used Subaru green coolant with Subaru conditioner and distilled water to fill up the system, making sure to back-fill the engine through the upper hose a little bit at a time to get all the air pockets out before I connected it to the radiator and filled the radiator up to the cap. I topped off the other overflow next to the turbo and then filled the reservoir up to the low mark. Engine ran perfect for the first two days and I kept an eye on the reservoir to notice any changes. I did notice that the reservoir would fill up well past the full mark and I would empty it down to the middle between the marks.
Now just today I noticed profuse amounts of white smoke coming from the driver's side of the hood and decided to have a look, knowing any residual coolant should have burned off by now. First thing I noticed was coolant was every where on my battery, below the reservoir, and on the engine itself, but it was isolated to the drivers side and wasn't leaking from anywhere, bringing me to conclude it was overflowing so much that it was squirting out between the reservoir and the tube that ran from the radiator into the reservoir.
So first I checked to see if the radiator was warm or hot to the touch but, infact, was as cold as the outside air (-2F here in Rochester, MN). At this point I am under the assumption I have a defective OEM thermostat that is locked closed and isn't opening when the engine reaches the optimal running temperature, causing the coolant in the engine to boil and overflow into the reservoir to relieve the cooling system of pressure.
I'll be taking it all apart again tonight to see what's up, but I definitely could use some pointers as to what to check for or if anyone has had a similar issue and knows exactly what it is.