Stick your wet hand on bare metal and it it sticks use a block heater
As an engineer, this is not what I call "data".
I don't NEED a block heater, but even at 20 deg f there is a significant difference in starting with a block heater. At my first coolant change I'm going to install one on my current tractor.
I have 150w Kats glue on heater on the oil pan and recently installed a 450 w block heater. This morning ( it has warmed up lately) - 5 C I turned on the key and looked for the glow plug light to come on NO light I thought what the **** somethings haywire turned the key and it started as though the engine had been warmed up. They had been plugged in approx. 3 hrs. but the timer had timed out at least 15 mins. before I decided to go start the tractor.