Since getting the XK8 I have noticed that when driving up long steep hills in warm/hot weather or in heavy traffic the radiator cooling fans often run fast, but usually return to slow within two or three minutes after the steep hill has passed. I recently replaced the water pump, thermostat, housing, hoses, flushed and replaced coolant etc, but the fans still came on high speed on the same long steep hills. ( of which there are many around my area )

Last week I removed the front number plate to do some other work at the front of the car, and realised that the plate is mounted such that it restricts air flow into the radiator grille. in fact it covers about 1/3 of the grille area. To improve this I made two brackets which have allowed me to re-attach the number plate about 2" lower down allowing more air flow into the radiator. ( and improving the look of the front end too ) The fans no longer seem to run fast going up the usual steep hills.

Whilst I was working at the front I noticed that there is no protection for the radiator underneath the front bumper/valance, and that any debris on the road could easily flick up and damage the radiator core. Is this normal, should there be a mesh/grille there to protect it ? I might fabricate something to be safe. The last thing i need is a dead rabbit wedged up there.

 

I would recheck the thermostat even though it's new or relatively new. Living in the San Fernando Valley part of Los Angeles, we typically have a minimum of 90 degree to 110 degree weather all summer and well into October. The only time I have ever had my auxilary fans kick on was when my thermostat went bad. And my license plate was mounted in the center third of my grill not allowing airflow either. Remeber that the temp. gauge will not give you warning before it goes all the way to overheated, and you certainly don't want that with the Jag's engine. Check to make sure the thermostat is opening and not installed backwards. I would wager this is causing your fans to kick on.