If it looks to be boiling, it's boiling and too hot.
My understanding is that older crockpots worked at lower temps, while crockpots in our food-police era work at higher temps from a sense that food should be brought quickly up to safely high temperatures.
I don't know exactly what the temperature thresholds are in either generation. But it does suggest that "low" on a modern crockpot is probably like "high" on an older one.
Some people go so far as to put some kind of electronic limiter into the power line in order to tone down the heat of modern crockpots.