2012 Chevy Cruze Cooling System - radiator & lower hose cool to the touch

TLDR version: Car warmed up, operating fine, radiator and lower hose remain cold to the touch. "Mechanic" confused. 

Mom has a 2012 Chevy Cruze. She bought it new, and it has ~55k miles at this point. She likes it, and wants it to be her last car. Maybe 6 or 7 years ago it sprung a coolant leak at the thermostat housing and overheated. I replaced the housing and thermostat and it has been fine since. Saturday she called in a panic stating that she had no heat and got an "engine overheat" warning as she was pulling into her neighborhood. I went over yesterday to take a quick look and found it to be low on coolant. There's evidence of leaking at the thermostat housing again, but no smoking gun. I topped off the coolant and drove it around for ~30 minutes with all seeming to be fine. It warms up to just below 1/2 temp on the gauge and stays steady. It makes plenty of heat. 

What has me confused is that even after a 30 minute drive, the radiator and lower hose are still cool to the touch. My first thought is a stuck thermostat, but I would think that if were stuck closed there would be overheat issues within 30 minutes of driving. If it were stuck open, I would expect at least lukewarm temps at the radiator and lower hose. I was short on time and had to call it a day. My next visit will include an infrared thermometer. 

These things are apparently well known for various coolant leak issues. There is/was a recall, but nothing active based on a VIN search. I'm not so concerned with where the coolant went at the moment - I know that I'll have to find/correct that. Right now, I'm trying to get my head around how it's operating fine but not building any temp in the radiator or return hose. 

Thanks! 

Low coolant lead to an air bubble in the system?

If the engine temp is stable, that means the radiator is functioning correctly.  Depending on the outside temp, the upper rad hose will go from warm to hot as the thermostat opens.  It then pushes the cold coolant out of the radiator, up the lower hose.  You will feel the tank get hot, but the core will only be warm for a few inches away from the tank.

Its when the lower hose is hot that you have trouble.

Streetwiseguy said:

If the engine temp is stable, that means the radiator is functioning correctly.  Depending on the outside temp, the upper rad hose will go from warm to hot as the thermostat opens.  It then pushes the cold coolant out of the radiator, up the lower hose.  You will feel the tank get hot, but the core will only be warm for a few inches away from the tank.

Its when the lower hose is hot that you have trouble.

Understood. In my experience, I expect some temp increase at the lower hose. It feels completely cold to me. That said, it was in the high 30s outside - my fingertip calibration may be off. 

Folgers said:

Low coolant lead to an air bubble in the system?

Highly probable, but I've typically seen fluctuating temps when there is a bubble at play. I'm not seeing any fluctuation in this case.