I've attached a blutooth ODBII sensor on the connection in the driver compartment and get real time readouts on my iPhone. While my dash temp gauge generally stays on normal mark, I can see that the temp readings from ODBII show it runs around 190F on the street, about 210F-220F on the highway and up to 240F going uphill, but the dash gauge never moved off normal. So that's a 50F temp swing that wasn't shown on the dash. Is this "normal"? Should I be worried about the 240F temp display? I've heard that the ODBII sensor may not be the same sensor as what the dash gets, but still, its 240F somewhere in the engine, isn't it? I hope someone has tried something similar to know if this is typical or not.

 

240 sounds a bit hot. The radiator fans should be cycling on around 215 to 220 max.

Are your fans cycling on?

The factory gauge is computer filtered to only move the needle up to about 185F and then again when the car is in a true overheat condition, normally above 230F on the 2003 and earlier XJ V8s. I am a bit surprised the trigger point is different on your later model car.

I make a module that converts the gauge to true operation for the earlier cars (see my website below), but unfortunately do not have one available for your car yet.

 

Thanks for the response. I've only had my XJ8 for a week now, but I never knew that temp gauges were programmed to only show an alarm situation rather than actually following the temp, interesting. So, from your description it would appear that, at least my highway temps of 210F-220F are OK, maybe even 240F is the overheat borderline. I wouldn't have thought a car would normally run at those temps. Back in the day, my '66 Mustang with a mechanical temp gauge at the water outlet to the radiator rarely ever got over 180F-185F, no matter what, so I'm just not used to this yet. If anyone has had any different experience with actual running temps on a 2004 XJ8, I'd love to hear what your numbers are.

 

I can't help you with actual running temperatures, but though the temp gauge is computer managed and doesn't appear to give any info, I have found over the 9+ years I've had my 04 that it actually gives very small movements that are quite useful in saying what is going on. When holding a steady highway speed, the needle should settle in to show just a smidge below the center mark, even on hot days. Coming to a stop light after a hard run, the needle will rise to show exactly at the center mark, or just a smidge above, and after a minute or two, will come back down to just below the center mark. If the gauge is showing on the center mark or just a smidge above most of the time, then it is time to check the cooling system (t-stat, coolant age/level, pump, etc). I recently replaced the coolant and t-stat in my car, and the outcome was very noticeable in the gauge's subtle "normal" readings. Being computer managed, the gauge will show "normal", else peg to the overheat position like an on/off switch.

 

It sounds like you have the typical failed coolant housing... these break apart internally and water can not circulate in the correct path through the engine and radiator.

240 is too hot. On the highway with the airflow of the moving car you should not see more than 205, maybe 210 on a steep grade. Mine usually holds at exactly 195 on the interstate no matter how hot. Temps up to 220 are normal, after that I'd start getting concerned.

And ditto what everyone else said above, the "gauge" on these cars are useless.

 

Thanks all for the great info, that does help a lot! Question to MHamilton: the failed coolant housing, is this something that I can fix, or are you saying that parts on congesting internal passages and water sleeves? If that's the case, it sounds like a bare block tear down and rebuild, or is it something less drastic that can be accessed or checked on externally? What would I be looking for to verify if this is what happened?

 

See item #15 (non-supercharged): 2004 JAGUAR XJ8 Parts - Direct JPLV Porsche Parts.com.

Just replace this whole assermbly for $95.06. It includes a new thermostat, sensor and all seals. It is just bolt on.

 

IC engines are actually at their best thermal efficiency quite a bit ABOVE the boiling point of water. Fewer acidic blow-by byproducts form in the lube - or remain there - as well. Primary reason cooling systems are pressurized is to support circa 215-220 F operation.

Your Muskrat would actually have been a tad better-served at a higher temp than 180-185 F, and AFAICS, the Jaguar IS 'normally' so-served.

240 F is out of-bounds, however, and remedial actions recommended should be chased forthwith before it worsens.

The all-aluminium engines just do not have a great deal of 'forgiveness budget' inbuilt, and we need to respect that.

 

Thanks for the great link! I'm just wondering, before buying this, does this housing / pipe section have a known issue with impeding water flow? I'm just thinking logically, because mine has no visual damage or leaks from the outside, so it would appear I'm theoretically replacing a section of pipe with a new section of pipe, I'm not sure how this would impact a hot running engine, unless my pipe has something inside that is obstructing the free flow of coolant. Is there something about this section that could cause a flow problem?

Thanks for all the responses, this is a great forum, especially for a Jag novice like me!

 

Item #15 would appear to be a bit more than just a piece of hose as you suggest. Among other things, Item #15 would appear to include a t-stat, which can very much impede flow.

 

just looked at your link

outlet pipe with Supercharger
MSRP $1100
Online price $875

 

Dudemann44:

I just read your link and was in some respects relieved but at the same time very concerned. My car, 2011 XJL with 82,000 miles just this weekend had the engine overheat. The only warning I received was that the coolant was low, at which time I put in about 1/2 gallon also the temperature guage never did move off the middle of the dial. Well the car stopped running and I had it towed into the dealership which they have so far discovered a bad water pump and heater hose but additionally it go so hot it melted the fuel line and when they tried to start it fuel spewed out into the ground. Also it appears that there may be damage to the head. The warranty insurance I purchased is sending out a claims investigator to review before they authorize any coverage. Already we are at $ 2,000 before they get into the engine issues. Not good that the guage does not work properly.

 

Yes it is, but I probably should have mentioned that I just replaced both the radiator and thermostat last week to no avail. So, taking the thermostat out of the picture, I'm trying to understand where or why there might be a flow obstruction in section 15 above. I hate to spend $100 on something that may not be a part of the solution. If you or anyone knows why this could be the issue, I'd love to hear what part or parts inside of this fail and hinder flow, if this case, I'll spring for it. The one thing I am going to do this weekend is back flush the heater core, since I have nothing but cold air when the heater is on. I imagine its related to my problem, and its basically a free and simple fix. Since the radiator was jammed up and replaced, I would think the heater core has something similar going on and, while improving circulation, may get my temps down. I'll post the results next week.

Right now, the faster I go, the hotter the engine gets, so its not fan related. At 65 mph it maintains about 220F, at 70mph=225F, 75mph=230F and so on. At idle, like a traffic light, it drops right down to about 200F and stays there until you get moving. Water pump??? Go figure, I'm puzzled....

 

In case anyone was wondering, it turns out the above symptoms were caused by a failed auxiliary water pump. If you see these symptoms stated above, try looking at this pump, especially if your heater is also blowing cold aid. Just glad I'm done with this issue.

 

B****y Hell. Who'd ha' thunk to even look for such a creature?

Trying to remember the last time I encountered a machine that NEEDED an 'auxiliary water pump', and IIRC it occupied a rather large and expensive hole in the water...

Thanks for the heads-up!

 

Updating my issue. the insurance company has now required me to have the engine broke down, about 20 hours labor, and will come out and do another inspection. at this point they have not denied nor approved the repairs until after the second inspection is completed.

 

Rumour has it that $75/hr shops still exist - somewhere, but I'd expect twice that as more likely, so $3,000 to tear it down - more than 20 hrs again to re-assemble?

Sounds like they are throwing up roadblocks to encourage you to just go-away - mad or otherwise - to me.