My 2002 XJR - Day before yesterday I noticed that the auxiliary fan kept running after I shut her down, which is something it never does, although it did shut off after a few minutes. The ambient temp was only about 78 deg. and I had checked the coolant level only a week ago. But yesterday it overheated on me. When I was able to open the coolant cap I noticed no visible coolant inside, but neither have I seen any indications of coolant leak, like on the floor, unless it only loses it during driving. I thought perhaps the water pump, but in my experience bad water pumps always leak and this one isn’t. Or is it worse, like cylinder pressure sneaking into the cooling system through a rip in the head gasket? Certainly need to do some tests.

I’m open to suggestions.

Thank you

 

You're right to be worried as those engines can easily be wrecked if they overheat.

Maybe there are some existing threads with ideas?

 

Sounds like a dead Tstat. Waterpumps as you say leak - have you looked at the coolant overflow tank? it's located behind the LH inner front wing cover, if the system overheats the excess coolant goes there, then as it cools it returns to the header tank.

 

I'm also thinking it may be the thermostat because, somehow, the symptoms appear to be that it is not losing fluid and then overheating as a consequence, but rather heating up first and then losing some coolant as a consequence of boiling, i.e. the coolant not completing its full lap because of an obvious restriction, most likely a thermostat stuck close (or a an idling/broken water pump, perhaps?) I just need to check all this before I go into major items.

Thank you.

Cheers,

 

Siding with Sean here, that's exactly how mine started to act up, and that was the thermostat indeed.
Watch it, if it all gets too hot, your secondary tank overflows (it is designed to do that, a simple hole), and you will need to fill up the system for lost coolant.

 

Sounds like mine, too, also the thermostat. Went last year around 98K miles.

 

Thank you all fellows for the feedback, it will be the thermostat first. I'm surprised at how easy and accessible the X308 thermostat removal is on this YouTube clip. Will hardly even lose much coolant.

BTW, is there a "better" or improved thermostat that I should rather get for this application?

Thanks for the info.

Cheers,

 

Not a better thermostat, so plan on replacing every 3-4 years when you do a coolant change.

 

One more question, where do I find the "header tank" and the access to it? I still can't tell from all these denominations, why so many names?:
-- Expansion tank
-- Header tank
-- "Fender" tank
-- Recovery tank
Which one of these is the one by the windshield next to the brake reservoir?

One last question... Can somebody tell me what is the specific reason why these cars cooling system need bleeding, or when? I've never heard before about having to "bleed" the cooling system in any of my cars, including my XJS.

Your feedback is much appreciated.

Cheers,

 

The R is self bleeding - coolant constantly flows with the ignition on, the auxiliary intercooler pump does this job, any air flows up to the header tank, which is located next to the throttle body, I've called it 'the header tank' because Jaguar have called it that on all their pre 70's cars, it's habit!

It's referred to as the 'coolant exapansion tank' on our cars, sorry for the confusion!

 

Well, the culprit was certainly the thermostat. Upon testing, the warming water pan came up all the way to sea-level boil temp (100 C, 212 F) and the old thermostat never opened. Conversely, the new one began to open at around 84 C. I also replaced the 100K-miles-old filler neck cap (the car's about 75 miles from reaching 100K). Topped off the fluid and went out for a drive with the needle glued exactly in the middle of the gauge's range once it warmed up. I guess that reaching boiling temperature for a real short time didn't necessarily cause any damage (warp) to the head joint surfaces. The engine ran very smooth and powerful as usual and certainly no leaks.

Inspection of the system's hoses, including the intercooler hoses, reveal that they don't look necessarily bad, considering that they are all the original hoses in a 100K-miles car. I also did notice how unusually easy to access and to replace they are, including all the intercooler hoses. I'm certainly going to purchase the majority of these hoses and get them replaced all at once for piece of mind. I wonder what else in the cooling system should be replaced at these many miles. Belts wise, the main serpentine belt was replaced about 1500 mile ago.

All your feedback and comments are much appreciated.

Cheers,

 

Glad you found the problem! Just waiting on my tstat to get here. Been having a problem with the fans running after shut off as well.

 

If you have no water pump leaks or noises, you're just losing cooling efficiency due to too slow coolant flow because of a malfunctioning thermostat, therefore the system has to be calling in for help from the auxiliary fans that otherwise it wouldn't need to. That's how mine started out, but soon the darned thing simply refused to open at all and when that happens, it doesn't take much time for the (not-moving) coolant in the coolant passages wrapped around the hot cylinders to start boiling. Luckily, I'm always paying attention to my gauges, so I was able to stop the engine immediately, which probably saved me from major consequences.

BTW, I bought my thermostat from the local AutoZone store for $11.99, including the seal, plus the "radiator" cap at $13.99 and a gallon of the Prestone Dex-Cool antifreeze for $16.99. The parts carry a 1 year warranty. I'm pretty sure that these parts (made in Germany and Israel, respectively) should be as good as whatever quality the actual Jaguar parts may be. There should be Autozone stores in Dallas, or similar.

The great thing in this case is how easy and accessible the parts are to replace, considering that we have a supercharger with its intercoolers right there. Even a water pump replacement appears to be not that complicated as per my service manual, and again, in spite of all the supercharger components in the way.

Hope your problem is resolved in a routine, easy manner and with no complications, like mine luckily (and surprisingly) turned out to be.

Cheers,