Put a new coolant bypass fitting and hose. Now, the car is overheating (almost getting to the red line) but the upper rad hose is not hot. Thermostat stuck closed, right? Could it be anything else before I change the thermostat (it'* about 2 years old)? Would low coolant level do this?

Empty radiator?

Yes an empty rad will over heat the car. Top it up and see if the problem subsides.

Nice sig pic, is that a black hood? Hmm noone has seen my car yet.

Offtopic, but no it'* green like Bills' car. From my 94SSE parts car, the spoiler is a slightly lighter green and the fuel door will soon match it.