Thanks guys for your advice.
My options are not so great. Down here near Cannes, France, there are no real Jag repair independents - only local Jag dealer!

? unless someone knows of one nearby I have missed?

The Jag dealer is only 5 miles away, just driveable without getting temp too high, other places would need recovery vehicle.

I will summarise:-

The car is almost 14 years old, 50,000 mils only, owned from new, serviced annually by Jag.

I heed your warnings not to drive the car (except to repair venue)

Since there was a slight overheat (55% with fans running) shown on the (I now understand unreliable) temp gauge (was always 45%!), until th Jag guy "did something" in 5 minutes yesterday (had said coolant was "too full"!
Then on the way home the gauge showed 80% approx, under the red area.
No warning lights!

I put on the Gendan and it showed 109° (229)F) and going up!

There has never been a coolant leak! (no orange liquid on the garage floor)

The coolant level has always been OK, as per the instruction manual.

Header tank is full.

I note your comments about possible temp sensor fault!! - and laser temp check.

?? Interestingly, to me, the radiator cap and surrounding area do not seem to be as hot as I would have expected in an overheat situation like this!

? is this indicative of poor circulation - or sensor fault ??

?? and would not such an overheat cause the coolant to overflow to the drain pipe ?

To me, as a relatively inexperienced guy (although I used to spend hours tuning the carbs of a Daimler Double Six in the late 70's and have changed the odd gearbox and Turbos in some lovely Lancias) I can't attack the S-type R.

I propose to do the following (my percentage golf shot):-

Go to my currently-booked service appointment next Friday, but tell them not to do the service until the overheat is fixed.

Ask them to:-(in this order)

-Consider first that there may not be an actual overheat if sensor faultty

-Laser test the temp

-Pressure check the system

-Check sensor (will their diagnostics show this though?

-Check themostat

Then; phone me, before wanting to replace water pump, or do any other costly work.

As you guys know who have older S-type 4.2's, there is nothing one can buy to give similar quality/comfort without spending many tens of thousands of £/$/Euros. But there will com a time when a harsh decision has to be made.

 

the temp sensor can not make an over heat but at can show a false one .
thats why you should back it up with a laser temp gun .
it sounds to me like the french mechanic removed the expanded coolant from the EXPANSION TANK .
thats why you check it cold as the manual says .
if the laser gun agrees with the gauge .
then
take the thermostat out and test it opens at the correct temp in a jug , or opens at all for that matter .
most likely its that .
if not the thermostat ,
id remove the water pump and check it has the pump is still attached to the shaft .
as a stuck closed thermostat or a broken water pump will cause both over heat and restricted circulation. has it had the stock water pump changed for the upgrade water pump in its life time ? i believe 03 and 04 V8/&R water pumps were revised. as the plastic was letting go of the shaft and failing to pump .

 

It's so vital not to let it overheat that I suggest it's not driven at all even if it has to be towed/flatbedded. If you can DIY fix it, or maybe get someone to do it where you live as an alternative to tow/flatbed.

If it overheats much it will need a staggeringly expensive engine rebuild (or new engine) which will cost more than the car is worth.

Bear in mind this car when new was a high end luxury performance supercar (as seen on Top Gear). They can break very expensively. You have to either DIY or pay...

 

If you cannot DIY then I would move overheat investigation to the very top of the list, never mind 'a service' by the dealer for now.

Could these people help?

Ferrari Rolls Royce Jaguar - Garage Spécialis

 

No, Datasports, pump was not changed.

I don't have facility to change water pump, but is thermostat easily accessible from under the hood/bonnet?

Will the Jag diagnostics show if sensor is faulty?
D

 

Looks a good place from the website, the dealer isn't confidence inspiring IMHO

 

The answer is a firm definite maybe. Any scanner, no matter how fancy, will only read what the sensor thinks it sees. If (big if) the sensor is inaccurate, you'd have to compare it to an infrared thermometer to determine if the value is accurate.

I'm not familiar with the Jaguar V8 temp sensor, but on other vehicles I've owned, the temp indication can become wildly inaccurate if the coolant level is low. Once the sensor is no longer submerged, I've had some instances falsely readng low and others high. I think the variation has to do with pockets of steam in the cooling system, but that's just a guess.

What I'm trying to convey is your temp gauge may not be accurate with the current low coolant level. Even if you topped it off, it probably needs to be bled to purge all the air bubbles. This is not a huge ordeal to do, but the dealership certainly didn't do you any favors by introducing a previously nonexistent problem.

My hunch is you had a minor problem to start. Could have been an actual temperature problem (bad thermostat, marginal water pump, etc.) or an indication error. Could be a combination of the two. Did draining the coolant cause the temperature to really climb that much? Or is it a false indication due to a pocket of steam?

That's why I've suggested undoing what the dealer did, topping off the coolant and bleeding the system. Get it back to the 55% indication you previously had.

From there, I'd suggest doing some diagnostic work yourself so you're not at the mercy of the dealer or other shop. You can get yourself an inexpensive infrared thermometer and see what's really happening. For $20 or so, you'd have a much better idea of the actual situation. Point and shoot, no wrenching involved. Just keep an eye on the temp gauge in case it is still accurate and the overheat indication is valid

 

I assume you went here:-
Jaguar Cannes
New, well fitted out, but part of ABC group having 3 or more dealerships in south of France.
Unfortunately, for me, the original Cannes dealer, with whom I had great relationship over 12 years, went bust - and I had to go to Nice for repair/service. Since there was a gap of 18 months before the new guys opened, all the "experienced Jag mechanics went to Aston Martin.
So I suspect thee is more Land Rover than Jag capability here?
D

 

Did you look at the link I posted above?

 

You may find my recent "overheat" experience of interest. Please note the difference of the V6 having a different type of sensor that reads the cylinder head metal, not the coolant. Despite this important difference, it's still a temperature sensor:

https://www.jaguarforums.com/forum/s...rature-186873/


In the end, after much headscratching and some panic, I discovered 2 out of 3 thermostats were bad, and also 2 out of 3 sensors were inaccurate. I never could have figured it out without an infrared thermometer to get a handle on the actual conditions

 

will this thermometer be OK? - Etekcity Lasergrip 774


Thanks kr98664

 

Also, the V6 can (sometimes? usually?) avoid catastrophic overheating. But the V8 CANNOT.

 

Yes, I think that model would be fine. It's amazing how inexpensive they are these days. Incredibly handy to have one.

I'm not sure exactly where to point on a V8. I have a V6 so there are some minor differences. Maybe somebody with a V8 can help.

If the thermostat is sending hot coolant to the radiator as required, you can test at the radiator inlet. This is where the upper hose connects.

One caveat: If coolant is not being properly routed to the radiator, you'll get a low reading there while the coolant will be hot back at the engine. For best results, I like to check both places, only I'm not sure exactly where on a V8.

As handy as an infrared thermometer can be, just be aware they are not magic. Like any tool, they have limitations. For example, with my recent thermostat debacle, I switched from a 192F version to 180F. At the front of the engine, there was so much hot air blowing back from the radiator, I couldn't see this minor drop in coolant temp at the thermostat housing. I could at the radiator inlet, however. There's a short learning curve to understanding the results, but I bet we could walk you through.

 

Excellent point. I had mentioned in passing to keep an eye on the temp gauge, but it's worth repeating. Make sure to avoid an actual overheat while troubleshooting. It would be a good idea to have a helper watch the gauge while you play with your new thermometer.

 

Thanks will do, and will plug in the Gendan to view the actual sensor temp on my computer.

 

Good informative link - will give them a call - thanks

 

I should receive an infrared thermometer today to check if sensor is correct or not, and temps around the radiator, thermostat in/out etc.

Forgive my many (due to inexperience) questions please. I have tried to look up diagrams on the web, but they are not always specific.

Please could you tell me where the thermostat is located - right or left of radiator as we look, and position? Is it accessible:visible or do I have to remove any covers.

See pics below.
To the left of he radiator, under the (full of orange coolant) tank there is the large pipe - is this in or out please? I'll call it Pipe1

*when cold this pipe squeezes easily! I assume it should be leess squeezable when hot and pressurised?

On the right side there is a metal pipe entering the top right rear of the radiator - what is this one? I'll call it Pipe2

In the centre, just behind the filler cap, there is a hose with a metal clamp which seems to go to the engine block, is this relevant? Pipe 3

Where else should I check the temps?

Thank you all for your ongoing help in trying to save my lovely car from leaving us!

 

Be sure to get the (free download or cheap on many sites) workshop manual.

 

pipe 1 is your top radiator hose .and it should definitely become hard with coolant pressure .
pipe 2 is one of your trans cooler pipes .
pipe 3 is no concern it's intercooler related .
test the alloy coolant manifold as the sensor is mounted at the back side of it .!
location of the thermostat is under the j pipe , the intake j pipe that goes from your air filter box to the oval alloy pipe in the center of your engine ,

so remove the plastic engine cover
then remove the plastic j-pipe .
and under there is an alloy coolant manifold with three t25 bolts holding the thermostat cover on . also it has the lower radiator hose attached to it .

heres whats under there .

 

Thanks Datsports - it's 10.30 am here in France, and I am now going down to the garage to do the temp tests