Last week I ran low without warning
My low coolant warning never triggered. I saw slight steam while sitting in traffic, and watched the temp gauge on on normal until the I got home and it jumped to red. (Good karma in driveway). Temp gauge told me red hot but sensor never warned me. I refilled to find the culprit as the radiator plastic-to-metal seal. Also replaced reservoir and low coolant sensor. It will be difficult to access this sensor for a change without pulling out the reservoir.
I still don't know if the new sensor is in force without running it low.