My "new" 1992 V12 coupe was finally delivered today, after months of waiting. So I promptly took it--I mean her--for a ride in the hills to stretch her legs. It is a blazing hot day, about 30 C (85F), and sunny so even hotter under the sun.
The car did not quite perform flawlessly. The temperature gauge would creep up to a few mm above the middle mark when climbing hills or the engine was stressed, and then drop down to normal or a hair under when cruising steadily. However, in town, and especially with the a/c on, the temp climbed to within a mm or two of the 3/4 mark. It seemed to hold steady about there, but I switched off the aircon for the last five minutes home as I didn't want to risk it getting any hotter for the sake of an experiment.
The first image is the max it got to out in the country, in the hills. The second is it in town.


Gauges after a run in the hills for about an hour. The temp varied between this and a low of a hair under the middle mark.




Temp in town, with a/c on, on a hot sunny summer day.

I called the seller, a specialist in older Jags, and he said that when they replaced the coolant, they measured the temps directly, and they were normal, so it may be a thermostat problem (just a thermostat replacement), but the temperature did seem to rise and fall consistently with what you would expect to happen based on airflow. The radiator uses the original yellow fan, which I am given to understand is not a great fan. The radiator itself was removed as part of the work, and I can't see any debris on it from outside, at least.

 

There may be a problem.

Or maybe not.

That it returns to a lower reading when unstressed (as opposed to continual climbing up-up-up) is encouraging.

IMHO anyone purchasing a V12 should go thru the cooling system from stem-to-stern just on general principle. Remove radiator for professional cleaning, new and correct thermostats, new fan clutch (and fan, if the older yellow type), proper bleeding, etc. The you'll know everything is up to snuff.


But....

Even that is no guarantee that the cooling system will hold thermo-rated coolant temp under all conditions, all of the time. Which is why Jaguar eventually threw in the towel and did what so many others have done: phased-in "idiot gauges" which hold a steady middle-reading under a wide range of temperatures

Cheers
DD

 

Thanks for the prompt reply. I was surprised to see just how variable the temp gauge was, after being used to a Japanese car with, I assume, an idiot gauge that never moved. Especially when I was keeping a firm eye on it to make sure it wasn't doing nasty things. It never reached the 3/4 mark at least, and always came back down with good air flow, but I am definitely going to take it to a garage as soon as I determine which is the most likely to know what they are doing. There's one about an hour's drive away on the expressway that the dealer recommended as knowing his way around a Jag V12, so that might be the place to start.
A hand-held laser thermometer has been recommended on some threads as well, so I might see about picking one up, and then asking where to point it.

 

Is the auxiliary fan working correctly?

 

It appears to be so (the smaller black fan to the left [facing front] of the big yellow fan, right?).
Whenever I shut the car off, I can hear it whizzing, and it shuts off after a few minutes. The engine is half-cool now, so I'm not sure how accurate this test is, but the main fan spins very little when spun by hand - just a blade's gap or so. I assume this means the clutch is fine. Unless it means the opposite. Or unless, being not completely cool, it means nothing.
The auxiliary fan spins a little more freely. Hard to be certain, as it kept hitting my hand as it was hard to move my hand out of the way fast enough.

 

Some Day, Some Day,

XJSs are really prone to losing the cooling fins in the lower third of the radiator. Have a really close look on the engine bay side of the rad, behind the rubber flaps (if still fitted). The symptoms you describe are really typical of that type of problem - lack of heat dissipation when airflow is minimal and a return to normal temp when airflow provides heat removal from rad.

You really do not want to overheat the V12! Very expensive, so get to the bottom of the problem.

The facelift gauges are a bit flaky, mainly due to earthing problem but the temp gauge is less prone to this problem. So, I'd start investigating the cooling system.

Good luck

Paul

 

Update: I took her out for a drive in town this evening with my wife, at sunset/after sunset, with the a/c on cold. The temp hit a few mm to the right of the middle mark, but no further, and when I could open her out, it dropped back to a fraction over the middle mark. It doesn't appear to be critically overheating, but it wouldn't hurt to get it checked out sooner rather than later, I think. The electric fan (aux fan) spun for about five minutes after getting back home.

Also, my wife hates it. Says the suspension's too firm, the seat too short front/rear and too slippery, doesn't like the windscreen wipers in her view, doesn't like the fact the a/c chills her feet and isn't cold enough on her face, and cannot believe you can't select between bringing in outside air and recirculating the interior air.
I'm a little surprised at that last myself, frankly.

 

Hi,

I have just been through the same thing with my cooling. I have only had this car for a couple months now, and when it was purchased, the gauge read about the same as yours. I however, didn't have any assurance that the system had been gone through. Now a month later, and the radiator is installed, albeit with cooler thermostats- the needle sits below the middle mark. When the radiator was pulled out, a third of it was full of debris. When the radiator was at the shop, it turned out a third of the core was full of stop leak.

I cannot imagine that my car was cooling effectively prior to the work, however the gauge didn't seem to indicate much of a problem. Has the radiator been recored?

Paul

 

I live in NE Florida and we consider 85F to be a cool day, not blazing hot. That being said my 86, V-12 runs just north of the "N" on 99F days with the A/C on and in traffic. On an 85 degree day it runs south of "N". I'd check for debris between the rad and condenser, make sure the foam is installed around the rad and the lower plate us in place between the air dam and subframe (most are missing). New, pepper thermostats might be in order to. Don't flirt with overheating in a jaguar v-12.

 

I'm pretty sure it hasn't. There's no mention of it. I was able to take a look earlier today through a narrow opening in the condenser, if I'm correct in saying that the immediately visible "radiator" seen through the grill at the front of the car isn't the actual radiator, and there were quite a few leaves I could see plastered against the rear part, the actual radiator. I'm pretty sure the shop had the radiator out - it, along with the replaced torque converter, was in a photo they sent me, so these may just be leaves I picked up today, but I would be surprised.

 

This could be what you may encounter.

 

Yeah, I've seen that nightmare pic. I really hope not....

JTsmks - I'll look up "pepper thermostats" and see what they are. I had a look under the car earlier today, and there is a wide but shallow plate stretching across the underbelly, under the radiator it seems, that appears to be the one you're referring to. And I think I will rethink my plans to move to NE Florida if 99F (37C) is normal for you - no doubt with plenty of relaxing humidity as well. My one visit to Florida was in December....

After another test run tonight, no a/c, it ran the usual mix of a trifle warm and just right in the hills, and then warm in town, even though it is night. By "warm" I mean it got to halfway between the 1/2 (midway) and 3/4 marks and stayed there. Not brilliant.

I will contact the place the dealer recommended tomorrow - for something like this I want a specialist's specialist eyes on it. I'll save fiddling with things myself for things that aren't quite so crucial....

 

most likely "proper" thermostats.

My wife likes the car. Neither of us like AC, so I yanked it out with the condenser. She had fun driving it last weekend.

 

Caution is good, no question. But to me, it seems your Jaguar is just fine. The guage tells it as it is. Far better than the "don't scare folks" stabilized versions now seen.


I like the IFR idea to measure real numbers at various places under the bonnett.


Yes, what you see from in front is the AC "cooler" not the engine radiator located behind it. It is that space as illustrated that gathers
the debris. Unseen, not good.


Forget stop leaks. An emergency measure at best. At worst, makes the realm issue even worse!!! Better, if it leaks, add coolant!! Old tech still works !!!


The auxiliary fan works. That is great.


These cars are partly chin breathers. The air dam is an important part. If damaged or gone, the radiator is deprived of needed air flow.
Hot good.


In a pinch help. If conditions are adverse. Hot day, slow traffic, etc.
pop the bonnet and let the hot air out. Immense help. Forward hinged bonnet good for this. Done on other critters from way back.


As to Thermostats. The correct specified working properly is the answer. Problem, modern sources don't always yield ones that work as they should. If any doubt, do the stove top test...


Enjoy that wonderful car. Think, but don't over think.....


Carl
Thsicar

 

Sounds like the wandering coolant gauge is the lesser of your problems.

If you're not used to seeing a gauge that actually tells the truth, like cars used to have, the needle movement can be quite distracting.

 

Sorry, I meant "proper" thermostats not "pepper" stupid auto correct😉

 

In my experience it is safe to say that your radiator is definitely not performing as it should. Get it removed, fins cleaned, fins of the oil cooler and aircon condenser cleaned out (the two things in front of the rad), and the inside condition of the radiator checked. Renew/recore if you have any iffy reports on that score. Renew all the hoses attached to the radiator and crosspipe as well as the thermostats. Get the parts from a reliable known supplier (eg Coventry West, etc). I think you are very sensible to take the attitude you are taking, and I also think you should do all these things ASAP. Do not allow yourself to be kidded that when you do a uphill run with the aircon on, it is normal for the gauge to the 3/4 mark. It is most definitely not. This is a clear indication that the system is not functioning properly.
Greg

 

Welcome to the site!
I had the honor to take graduate level Koto from Yuko Wada and Yuriko Matsuyama while at Florida state University in 1980

91 to 95 F here in NW Florida and the electric fan comes on when the needle is 1mm to the left of middle... here it does not go past the middle...
I had pin holes in my radiator so I replaced it w a wizard cooling AL one
some one here (G-D Bless them) pointed out that the Yellow fan had cracks in it.. the common failure with the yellow fan.... I picked up a new replacement Black one....
I did not replace the fan clutch (shame on me) (just found one for 15.00 free shipping)
the electric Fan it has been coming on al lot more lately so I am going to replace the fan clutch... as the temp has been creeping up at red lights and dropping back on open runs...

watch for leaks .... and a temp gauge that high would give me great pause....
I'll take mine for a run the long way home and post the temp picture(S)... with current air temp...


Please pictures of your lovely Car and Countryside...

 

Get a cheapo IR thermometer to see what the temps actually are.

Did you say it cooled off at speed? Maybe check the mechanical fan as well, see if the clutch is good.


What exactly does your wife drive/is your suspension in working order?
The XJS has a fantastic suspension, it devours the highway. The same suspension in the XJ12 was quoted as one of the most comfortable in the world by Jeremy Clarkson.

I've driven new cars that are less comfortable than my 30 year old bushings. I blast over speed bumps that others slow down to a crawl for. If your wife thinks it is hard, there is either something wrong or she drives around in a squashy suburban most of the time.

 

Thanks for all the replies. Very helpful indeed.
I've heard about the releasing the bonnet trick in a pinch, but didn't try it as I was checking how hot the car was getting, with eye firmly on needle (if it ever went over the 3/4 mark in town I would have stopped and opened the bonnet fully).

I'm going to get an IR thermometer today if I can, so if anyone can help me with where to point it and what temps to expect, that would be great. I'll also have a search in the forums for similar advice.

In terms of the suspension, I think it's in working order - the front bushes were replaced by the dealer before I got it, in addition to removal, adjustment and repair of the steering rack and front camber adjustment. There's a dip and bump along the a road near my place where my wife's little car feels like it's hit a deep well, and the XJS barely even registered it, for example. But it's not wafty or isolating at all. The suspension feels firm, sort of like a sports car. This is not just the first XJS I've owned, it's the first Jaguar I've owned - or driven, for that matter. So it's very hard to compare.

The car corners wonderfully, to the extent I've dared push it on twisty mountain roads, although I haven't yet taken it to highway (100 kph / 60 mph plus) speeds yet (the open road limit in Japan is a max of 60 kph - I might have gone beyond that, but not triple figures).