My well-maintained '07 XK with 80K miles has displayed an odd behavior for over 5 years that I have yet to find an explanation for. After driving the car and shutting off the ignition, the cooling fan will start, or sometimes increase in speed if it is a very warm day. What is unusual, for me at least, is that the fan runs for exactly 4 min 0 seconds at ~50% maximum speed and then shuts off. It does this most - but not all - of the time. I have made numerous runs while monitoring and recording fan speed along with ambient temperature, coolant temperature, engine rpm, and vehicle speed. The fan behaves independent of the other variables, other than coming on while stopped at a stoplight/sign if the coolant temperature exceeds ~195F. Perhaps there is a sensor sending out a signal that leads to a default-mode operation of the fan. What may be relevant is that the fan also operates intermittently when cruising at steady speed on the freeway and elsewhere. It will come on, run at varying speeds (up to 35%), shut off, start up again, and repeat randomly with varying fan speeds. The fan speed reads 9% when the engine is first started from cold, but I can’t see the fan to confirm it is rotating. This reading could merely be an artifact of my AutoEnginuity DTC software. The fan speed reads zero after the engine is shutoff and sensor outputs are still being read.

This is not a major issue since the car never overheats, even in back-country San Diego in the summer. All cooling system components have been replaced and everything checks out as expected. While not a big deal, I am very curious what could cause this.

Thanks.

Dan

 

It sounds like normal behaviour to prevent remove hot spots which can peak immediately the engine is stopped.

Richard

 

Good point. I am not aware at that 4.2L engine has hot-spot issues upon shutdown. The car didn't do this for the first 4 years I owned it and none of the member XKs in the San Diego Jaguar Club exhibit this behavior nor does my '11 XJ 5L with 140K miles or any of the other eight Jags I have owned. Given the random on-off when driving at constant speed, I am suspicious that the electronics in the fan control module housed in the fan are starting to fail and causing the issue.

 

Please see the 3rd warning from page 1534 / 4000 sourced from the service manual to an '07. And the next page.

 

Thanks. I do recall now reading that input from these sensors, i.e., ECT, climate control pressure-transducer and transmission oil temperature, define fan speed. I have monitored the ECT and can determine no basis for the fan coming on when the engine is turned off or for going on/off when driving at steady speed. I have also made runs with the A/C on and off - again, no correlation. I have not monitored the transmission temperature. I'll make another run and plot it along with the others.