A 50/50 coolant mix protects to about -34°F, which covers NYC easily. But coolant degrades, and a topped-up cooling system that's been bled with plain water can drop the freeze point to dangerous levels by year three.
A cheap antifreeze tester (under $5 at any auto parts store) tells you the actual concentration in 30 seconds. If you're at 60/40 or better, you're fine. If you're at 30/70 (water-heavy), drain a quart and replace with concentrate.
Frozen coolant cracks engine blocks. If you've been driving with low or weak coolant and the engine starts running hot, stop and call. We tow flatbed to your shop at our $249 / hour rate — same as every service.