Hi all, I need some advice. 2004 XJR 130K. Recently I had a cooling hose leak. Replaced that and upper rad hose. Bled system, installed Jag coolant, cars runs great. Cool weather in Cali, but the cooling fans run hard almost ALL THE TIME. No coolant loss. I did notice when the rad hose went out that the Temp Gauge was garbage and unlike my other non Jag cars the XJR reads either at the halfway point (where it lives right now) or straight to the red, where it went after the hose went south.

After trolling the threads I read similar sentiments about 2000 2002 temp gauges being worthless, and most threads point towards a bad thermostat which I am thinking of changing?

Before wrenching on it again I wanted to get some feedback. Do the cooling fans ever go nuts? Is there maybe a temp sensor related to the fan that goes south, or is the thermo the most likley point.

Again feel a bit blind as the temp gauge reads perfect and some of the short drives should not even open the thermostat let alone turn the fans on full? Maybe it is partially opened?

Any thoughts or input is appreciated. Always great help here.

 

Typically, the cooling system returns to normal operation after service. I'd recheck everything and make sure nothing was missed, particularly as it relates to bleeding.


I think there is a P-code if the sensor has failed and the Check Engine light will illuminate. Are you seeing anything on that front?

 

Thanks RC. I bled it twice just to be sure and there was flow after the last bleed so I dont think there are any airpockets. That said it is not throwing any codes either. I will continue to poke around but for now I am still stumped.

 

Do the fans keep running off and on once you shut the car down? During a wash I quickly passed across the passenger (US) side underhood fuse box, which proceeded to blow open due to a broken lid. After this light dusting, the cooling fans did go nuts for the rest of the afternoon. I actually unplugged the battery because they wouldn't shut off. Once I figured out what happened, I heat dried the fuse box and the fan issue went away.

Don't wash under the hood on Jaguars, LOL.

 

No they just run at a high rate and shut off normally with the engine off. Good call on not washing underhood but it is just running abnormally high and presumably all the time while I am driving.

 

Definitely change your thermostat, they do fail MUCH more often than the engine temperature sensor. Thermostats really should be changed whenever your coolant is replaced. They are cheap and really should be considered a preventative maintenance part.

 

Second on the thermostat...

https://www.jaguarforums.com/forum/s...ad.php?t=87243

Thanks
-mag

 

You need to check what the engine temperature actually is.

Easiest way is with the Engineering Test Mode in the instrument cluster. Hold down the trip computer button on the indicator stalk and start the car. Keep holding for a few seconds & then release and you will be in the test mode. Cycle through the tests by pressing the trip computer button on the stalk till you get to the Engine Coolant Temperature indicated in the trip computer display in the instrument cluster.

I can't remember if it will show in ºF on a US spec car, but the values will be there without a decimal point, i.e. 0961 = 96.1ºC

The reason to actually check the temperature is that the fans will run flat out if there is no connection to the Fan Control Module, it defaults to flat out. If the temps are low & the fans run full then it's a wiring problem to the Fan Control Module.

If the engine is actually hot then yeah, check the thermostat. Another way to check if the thermostat is jammed cold is the main hose on the left top when you are looking at the engine from the front, it will be soft with the engine running if the thermostat is closed.

I've had to replace the thermostat on my XJR, so it's fairly common for them to give up.

 

Just had a similar problem when changing the coolant on the wife's Genesis. Gauge went to zero, fan stayed on all the time. P0116 Temp Coolant Sensor out of range/performance. I had managed to get the connector wet and it was v difficult to get at. It dried out on the way back from work. If its the ECT sensor you will also get a higher fuel burn till its fixed. ( fuel injectors stay in open loop)

 

Off topic a bit, but can you adjust the font in your signature? I just about fell off my chair!

 

If the temps are ok but the fans are always on check the plug for the fans.
There are 2 plugs behind near the S/C coolant pump
One caries the power and the other is the fan speed signal

If this plug is off the fan will run flat out all the time

Do a search for "fan Mod" i posted pics of the plugs there


Cheers
34by151

 

This is very helpful thanks. Did not know that was an option.

-mag

 

Awesome replies all around. I had some family issues (dying relative) so I have been out of the mix for the better part of Feb so thanks everyone for posting. Just getting around to the repair and changed the Thermo. So far so good. I flushed and backflushed everything clear and then buttoned up and refilled. The bleeding is taking forever. Seems like a TON of air in the system. Huge rainstorm for So Cal so I will get it off of the ramps and road test after another bleed. I will update everyone on the final prognosis. Thanks again for all of the replies

 

Just to update everyone, I replaced the Thermostat, did a correct bleed, and all is right with the cooling system. Thanks all for the replies and good advice!