While driving this evening in 35 degree weather the temperature gauge spiked and the car went into limp home mode after 65 miles on the interstate at 80 mph. I pulled off the interstate as soon as I could and opened the hood. The engine was cool the coolant was warm and after letting it sit for 15 mins I started it up and all gauges read normal.

I then proceeded to drive it and the temp gauge dropped from the middle of the gauge to cold, the car made it the remaining 15 miles home no problem. Any ideas what is wrong?

 

Sounds like a stuck thermostat to me. It may have freed up when you stopped.

 

had the same problem on my xtype too.. changed the thermostat and all is well...

 

Hi guys, spare the newb a few min.

My recently purchased '03 3.0 SE is doing something very similar and while the signs point to a faulty sensor, not knowing the finer details of the car makes me question my logic.

SA tends to be fairly hot and while driving in fairly warm conditions (24-28deg C) the motor seems to run very cold with the needle hovering around the 'quarter' mark (25% from max). Chatting to a friend with a 2.5 he says that usual operating temperature is around the half mark or just below.

On occasion, not necessarily under load, the needle will move to the half mark but then it's only a minute or two before it runs to the red. Switching the car off and then restarting sees the needle return to the 25% mark.

Coolant level is fine.
There is no water loss.
Minimal pressure in hoses when 'hot'.
Minimal heat in hoses when 'hot'.
No unnecessary radiant heat from the motor when 'hot'.

Cooling fans seem to have been hard wired to run permanently. (This worries me)

 

Previous owner probably hard wired the fans to bypass the fan control module, which failed.
If I was you I'd start looking for a working module to replace yours and get your system wire back to factory specs. After that's done then you can look into the reason for the low reading on the gauge, if it's still reading low. You really don't want the fans running continuously.

 

Thanks Green Machine.

I did notice what seemed like a heat-sinked module of sorts on the front slam tray that had been disconnected, wasn't sure what it was for though. Would this be the fan control module that you're referring to?
I agree, a engine that runs too cold is just as bad as a motor that runs too hot.

 

Spyke, yes, the finned module on the fan assembly is the control module for the fans. Unfortunately, I think you are going to find that the only way to get the finned module is to buy a complete fan assembly (both fans, the plastic mounting, with the module).

As for your erratic thermostat temp reading, I would replace the thermostat in the car first. It is an easy thing to do and that should fix your issue. With the hoses under the hood/bonnet being cool to the touch, that is telling me that the engine is truely running too cool. Then what is happening is once the thermostat unsticks itself, it is slamming wide open. This is leading to the coolant passing too fast through the radiator, not allowing it to be cooled enough. Therefore you are feeding hot water back to the engine.

If you need more help, let me know. Thermostat job is easy. Hardest part of that is getting the clips off of the thermostat (pair of neednose pliers does the trick). Replacing the fan assembly isn't hard, just need to have the front end of the car raised up a little bit so you can slide the fan assembly out the bottom (would be a good time to do it with the thermostat changeout since you will have the plastic deflector under the radiator removed anyways).

 

Great advice, thanks Thermo. (oddly appropriate handle there btw)

 

Spyke, if you knew what i did for a living, the name would make all that much more sense. When I got the handle, I was a nuclear reactor operator on a submarine pushing around 24 nuclear tipped missiles. Actually, the name is short for Thermomonkey (or Thermostatic Monkey). Believe it or not, running a nuclear reactor on a submarine is some of the easiest work I did. Gotta love a job where you sit on your hands and not touch anything. But, I have retired from that job and now work at another nuclear power plant maintaining all the electronic and low pressure control systems for the nuclear reactor. What a cake job that is. I'm loving it.

P.S. I could teach you how to run a nuclear reactor in about 5 minutes and that would cover 99% of what you need to know. It is that 1% that gets most people. But then, that is why I also picked up the nickname "Homer". BUt, I digress. Oh those were the days of living on the edge.

 

Yes, as Thermo said that finned thing is the control module and it isn't available from Jag by itself. However you could check around at salvage yards to see what's available. When I replaced mine going on 3 years ago now I picked up the complete fan assembly, that's the 2 fans, shroud and control module from a 2004 X-type for $100. I simply pulled my module and put in the new/used one and was back in business. Plus I've got a spare shroud and 2 spare working fans. Big savings over the cost of new parts.
This is the place where I got my parts: Nationwide Auto Recycling http://nationwideautorecycling.com

 

the fans may be hardwired for a different reason... the module or controller may work, try hooking it up before you go spend money.
we had to hardwire the slim fans on the track cars we built, if the car wasnt moving it would overheat on one of them, so the fans had to be always on.

 

I saw your post on that while searching. I'll troll the local breakers and see what is available - the US site isn't too much use to me yet.