I was sitting in traffic today when my '03 XJR overheated. I shut it off almost immediately. Did a pressure test it was good. No water in the oil. Filled it back up with water and let it run in park for about 10 minutes, no problems or codes. I then drove it for 15 or so miles. No problems. Any guesses what happened? Ive, got a couple of ideas but don't want to sway any answers.

Jeff

 

Filled it back up with water?

No low coolant message?

Either the fans didn't come on or you have a sticking thermostat. More info needed.

 

My 02 did a similar thing once. As a precaution I replaced the thermostat and the water pump.

I think that when mine overheated it was due to an air bubble in the system that just happened to be in the right place when the car was stopped in traffic for a long time. I had previously had a burst coolant hose and added coolant and did the repair without purging the system since I did not know there was a special procedure for purging the system.

There is a rather detailed procedure for purging the coolant system of air pockets, something like turning the ignition to position 2 with the cap off the overflow tank for 2 minutes. then opening the coolant port on the top of the supercharger air output (19mm hex socket) then adding coolant there if needed, etc. If you need the exact procedure I can look it up and post it on here.

 

Yes water for now. The low coolant switch needs to be replaced, it is intermintent. The overheat happened after a 20 mile drive, thus I don't think thermostat. Agreed, fan didn't come on, but must have late, I let the car run for at least 10 minutes in park. Fan works or doesn't right? What tells the fan to turn on? Where is the relay? Those are my two guesses.

 

It was the fans.