I have read as many forum pages as i can, but I would like some local opinion.

1999 or 2000 Jaguar Sovereign LWB 4.0 litre V8.

I know the temperature gauge is not very accurate, and tends to show normal (1/2 way) over a large range of temps, but just recently, my car started to overheat. I drained the radiator, the coolant was fine, and it certainly seems to circulate OK. It only overheats when standing still, or even when it is turned off after a drive. Seems to be OK when moving in free flowing traffic.

One day last week the air stopped working, the temperature gauge shot up, and and at one point it even seemed reluctant to change gears. I stopped, allowed the car to cool, checked the radiator, then drove home (2 hours later) and the temp gauge was completely normal (I have ordered a Real gauge package so my temp gauge actually works correctly).

The interesting thing is before the over heating, I had a small squeal in "one" of the belts (slipping?) after starting the car. This noise went away after a minute or so of idling or driving. But now, the squealing noise is gone completely. Does this mean I have broken a belt? I have looked and just can't see anything missing under the bonnet. Am I missing something hidden or really obvious?

Any suggestions on what might be going on? Your help is greatly appreciated.

(Sorry, one other thing, do I have an x300 on an x308? The compliance plate says 1999, and the forum says 1998 -2003 is an X308, but the sticker on the wheel arch says x300)

 

G'day Corsa59. Sorry it took a while to respond!

Mate I am an XJS man myself but I would think if you have an 8 cyclinder you would at least have an X308. The X300 didn't come in an 8 cylinder if I am not mistaken (I am not an XJ expert however!)

I know you have looked there but there would be a few local guys lurking around the XJ section here I am sure:

Under Jaguar Models (Modern)

XJ XJ8 / XJR ( X308 ) - Jaguar Forums - Jaguar Enthusiasts Forum

XJ XJ6 / XJR6 ( X300 ) - Jaguar Forums - Jaguar Enthusiasts Forum

That heatsoak is pretty harsh on the electrics on the V12 I know and being we are pretty much in the same area in QLD I can relate with the type of weather we have had lately.

Sounds like you got an issue with your cooling fan. You mentioned last week the air stop working? Have you got a bad electrical connection for your cooling fan perhaps? I had the same problem a year back where she would start to get real hot, but most noticable when I was idling or at a standstill. Driving along she would go back down. Opened up the bonnet to find my cooling fan was not on at all when it should be! I had a bad connection on mine, easy fix, although not familar with your particular wiring circuit. Does that fan kick on when it is supposed to everytime? My temp gauge gets just below the "N" when mine will start.

I also have some pretty common modifications on mine to improve cooling:

Cold Air intakes: From the factory mine use to suck it from the middle/front of the engine. I now have cold air sucking in via some ducts either side of my wheel wall.

Cooling fans: From the factory my model has a belt driven fan but the P.O took it out and installed an electric twin fan set up from a Ford Falcon. Much better air flow.

Also this year I have swapped out the water pump with a good mate of mine. It was so/so with sticking bearings.

And finally, when I originally got mine 3 years ago she used to overheat going up to Maleny from Landsbrough up that bloody big hill. Cause? Coolant was circulating but the radiator was 60% blocked! Took it into a rad shop to get fixed.

Anyway mate, I am definitaly not an expert on your model but there sure is some guru's floating around that could help you more.

Be sure to check out the X308 thread, and what I would do is start a thread, and I am sure you will get a response in about a day!

Good luck!

 

First up make sure the coolant is full and the air is bled from the system.
If you have air in the system it will overheat!!!

Next are you loosing coolant?
If you are you have a leak to find

Next are any of the belts broken or missing?
If you have lost a belt the water pump wont be working

Are the fans working?
If you checked all of that the most likely issue will be the thermostat followed by the water pump. Least likely is a blocked radiator or engine water passage.

It would also be worth replacing the oil and checking for water which is an indication of internal seal issues caused by cooking the engine. There are some other things to do like a pressure test on the cylinders but get the basics above done first


Cheers
34by151

 

My 99 S-Type V6 goes into limp home mode whenever the temp gets too high. I'd be instigating why yours doesn't do that too, as it's a definite engine saver.

 

Oh, mine goes into "limp mode", not necessarily when it is hot, sometimes immediately after starting. Often a sharp stab on the throttle with pop it out of limp mode. Other times I just need to shut it down and restart it.

I suspect it has something to do with the ABS/traction control module. For 2 years I have driven the car without traction control or anti-lock brakes. As I only drive it on special occasions, and not when it is wet, I don't mind not having them. My other car has no traction control or ABS, and I don't think I have locked my wheels up or spun my tyres in over 20 years! My dash is like Christmas all year round!

Strangely it did not go into limp mode when it was very hot.

I might be completely wrong, but it appears to me the engine only has one belt. Is that correct? I just can't see any pulleys that aren't connected to the serpentine belt. The water pump is definitely driven by the main belt.

I am starting to think the water pump may have been causing the noise on startup, and when it failed completely, the noise stopped. I don't want to pull it to pieces before I get the parts. I have ordered a new water pump, thermostat, an alloy thermostat housing and a new belt from the old dart, and when they arrive I will remove the belt, pump and thermostat, and replace them all.

I will let you know what I find.

 

So, six weeks on, the parts arrived in early January, I was in the USA and Mexico for all of January, and for the last two weeks I have been catching up with work. So nothing has been done on the car.

Today, I removed the serpentine belt, removed the water pump, and removed the thermostat. Both looked OK, so I suspect it must be radiator related.

I bought a metal thermostat housing to replace the plastic one, but chose not to fit it at this point, not sure why, maybe because it looked like I needed to remove the intake manifold to fit it, and that was way too much work for one day.

I fitted the new water pump, thermostat and serpentine belt, a really easy job, but doubtful it will improve my position. Of course the battery is flat because it wasn't turned over whilst I was away because of the overheating problem. Charging the battery now. I will get it started tomorrow, see what noises it makes, take it for a drive, and then decide if I need to remove the radiator.

I will let you know how I get on.

 

Hope you can get it sorted mate.

 

Good luck!