First of all, the glass jar will not break because the water has space to expand UPWARDS, with the air having 4 routes to escape (HHO outputs, safety check valve and bubbler valve) and to make more room for the expanding water. So just in case it does freeze, it will not break anything.
The electrolyzer is capable of thawing itself in a few minutes. Start the engine and let it run for a few minutes. The electricity running through the spiraled electrodes acts like a heater and will melt the frozen water. This is safe to do because this heating process happens all the time anyway.
The best substance to PREVENT freezing is using windshield washer fluid instead of water. It's mostly water and it cannot freeze. If you need to add some more fluid, you don't have to take the device apart. Just take off the bubbler cap, inject some fluid through the hole and put the cap back on.
Optionally, use the "Charged Water System" which is a simple yet powerful system. In the charging process, charge a mixture of half WASHER FLUID and half tap water. In this case, the process will suffer somewhat in the winter, that is to say will not be as efficient as summer. Gasoline, diesel and veggie oil or bio fuel, none of those are as efficient in the winter. Yet I think it's better to do something than nothing.
Practical ideas based on user feedbacks