Still trying to learn things about my xj. When should that second fan come on? Can anyone direct me to any good reading on the second fan?

 

It should come on over ~217°F or when you're running the A/C or Defroster. What year XJ?

https://www.cherokeeforum.com/f2/att...osting-268677/

 

91. I’ll run some tests. So far haven’t gotten above 210, but I didn’t turn on a/c or defroster

 

As it's a '91, not sure if pulling the wire off the temp. sensor will trip it.

 

Pulling the connector off the thermostat sensor turns on fan in a 92. , as does turning on ac or defrost..ONLY if there is enough freon to engage the ac compressor clutch. Pulling the sensor connector will trip a check eng light /code

 

Pulling the connector will tell you straight away whether the fan's working (but not, of course, if it's coming on when it should). I didn't mention the CEL because you wouldn't know, as you can't see it from under the hood & having reconnected it, the light will operate normally after the next start.