Looking at my handy chart (I deal in industrial chillers at my work):
25% = 14F
30% = 10F
40% = -6F
50% = -28F
Keep in mind the pipe burst rating is much lower temps. Meaning the freezing point is when the liquid is sitting in an open bucket and starts to turn into slush. Slush won't pump, but it won't destroy piping. 24% will get your burst protection to 0F, which is probably all you need.
To be honest, most cars probaly don't need 50%, but they are some and operated in such a wide range of location, that they play it safe. FWIM, we use 20-25% in our chilled water system so we can run 32F water temps, keep CW coils in 100% outside air handler from bursting if hte pumps or steam reheat fails, and lastly, I think 15-20% is needed ot prevent bacteria growth... obvisouly not an issue in a hot water boiler that runs over 120F.
Maybe just try dropping the glycol percentage and see what happens.
I guess I didn't think much about it.
Lowest I seen my thermocouple buried in Concrete showed 32F