Odd erratic engine temps

[fixkick]

one can drive and run obd2 scanner and plot ECT  like this,
here is dead dog slow (snail) thermostat, it works but is super slow. slow and reads too low even after many miles. classic 7+ year old thermostat (yours is not bad)
but can float and run as bad, ok?


if you keep driving and logging the light blue line when fully hot 180F,  is steady at all times, if yes,  it's not bad nor floating (each step is a scan by the tool) looping scans.
ECT light blue.