www.jec.org.uk

1991 Le Mans Pre-Facelift 5.3

Is there a recognised test for the operation of the fan?Im suffering "overcooling",gauge barely reaches 70C even after a long run + revs at 1000 ish when idling,fan spins when engine cold.

Does the LeMans gauge have the temperatures on it rather then just marked C N H ? I'm not familiar with them.
The torquatrol units can sieze with the added danger of the fan flying apart but there are many differing ideas on how to tell if its correct or not. Kirby Palm's book gives some interesting discussion on the subject, click on the 'technical' button at the top of the page for more information.
First things to check would be the thermostat(s) and the accuracy of the gauge itself I would think.
Pop

Best way of testing thermostat without taking things to bits and breaking gaskets is just point an infrared thermometer at the cylinder head and read off the degrees. They are not expensive to buy now about 20-30 UKP.

When the torqa slip-thingy jams solid while you are driving, I think you'd notice it. It happened to my freind's xj-s and made a real whoosh sound when engine revved. When the bonnet was lifted, there was almost a hurricane of air!

With the engine stationary and cold, spin the fan by hand. It should come to a stop within one revolution. If it's seized it will make a lot more noise than usual, if it freewheels it won't do much on the cooling front.

However, if the temperature doesn't get above 70, it's not the fan's fault and much more likely to be the thermostat not fully closing.

Thanks for the comments guys,sorry its a while in responding but I wanted to do some thorough tests.Answers to your questions :
The gauge is graduated in degrees C,the green section is 90 to 110 ish,min reading 50.
Used contact thermocouple for tests.Tested the fan and torq jobby as suggested,it spins free when cold and does stop within 1/2 to 3/4 of a rev.
I carried out a test from cold,car at standstill,indoors with ambient 15 - 20C
Viewed from front of car,temps took at each thermostat housing inlet,next figure is top hose return into each side of rad,next figure is rpm,temp gauge reading,then oil pressure.Test took about 30 mins.

L/H bank
13.3/13.3/1400/<50/80 Temp sensor reading 3.589 K ohms
10 mins in 63.7/65.1/900/50/75
20 mins in 87.2/78/800/72/55
30 mins in 83.4/73.2/800/75/40

R/H bank
13.3/13.3/1400/<50/80 Temp sensor reading 3.589 K ohms
10 mins in 81/72/900/50/75
20 mins in 86/72.5/800/72/55
30 mins in 90.1/77/800/75/40

Tested reading of temp sensor after test and:
At 94C 180 ohms
At 95C 174 ohms

As you can see revs do die off,oil pressure is as it left factory,sensor it would appear is as spec,but gauge is out.........probably gauge?
Pleased I went through this exercise though...put my mind at rest !!! I think.

Pop,Heres the instrument panel hope this works

http://www.jec-xjs-forum.org.uk/xjsbb2/ ... 2-1_tn.jpg

Thanks Leon, thats a really nice instrument pod. Very similar, if not identical to the Series 3 V12 Sovereign I used to have. Are all the LeMans like that or did you convert it?

A few years ago driving along, I glanced at the gauges and had kittens when I saw the temp needle way up over the red zone. After much panicking it turned out to be a faulty gauge. The sender is cheap and easy to change and might be worth trying first as the gauge is much more work to get at.

Mine is the 'barrel' gauge so there may well be differences, but I found one of the resistors had failed, I couldn't determine exactly what value it should have been so I replaced the whole gauge. With hindsight I should have measured the replacement and then repaired the failed one to keep as a spare.
Pop

Thanks Pop.
The instrument pod was fitted when I bought the car,I havent had the pleasure of seeing any other Le Mans versions so wouldnt know if its an original feature or not.I wouldnt be surprised if its the same one as the S3 V12 Sovereign,I seem to remember reading somewhere about Jaguars "mix & match" policy years ago
I will check gauge but I think its off ECU,Ill get the books out.
Lovely car V12 Sovereign,always wanted one of those.

Leon,

Someone has changed your instrument panel. That's not an XJS panel that is fitted to your car. It looks one from a Ser III XJ12. A Le Mans XJS should have a standard XJS panel with the barrel gauges for minor instruments.

I suspect that is the problem. As you've successfully tested the 'stats (those readings look about right for an 88 degree 'stat), then I would guess that you have a gauge in that new cluster which is not in calibration with your sensor.

I think that MarkB wrote a post sometime ago about how he could set a gauge up correctly with some thermocoupling doubler... (or maybe I'm having an XJS fantasy????)

Anyway, at least you know that you probably haven't got an engine / 'stat / cooling problem.

Paul

Thanks for the info Paul,looks like Ive got a hybrid then,I thought that being a late pre-facelift it may have been subject to changes.
The temp transmitter however on Ser 3 V12 is listed as a DAC 2583,as is on the XJS Does anyone have any test figures for this transmitter? Ive got readings for the temp sensor for the ECU but not the gauge transmitter.
You may be able to answer my question on the 2 x red lights on the instrument pod top,what are they for? My handbook doesnt show these (reason being all too clear now)
Good to know the temps are ok though

Does anyone have any test figures for this transmitter?
With the sensor wire unplugged (open circuit) & ignition on the gauge should read full cold, with the sensor wire earthed the gauge should read full hot.

When I tested mine, test resistors gave the following approximate gauge positions:

H 22 Ohms
N 60 Ohms
C 100 Ohms

Pop

Thanks Pop,
Ill test it in week.

Tested the transmitter for the temp gauge,at 8 to 10 C it measured 1500 ohms.

<..>
I think that MarkB wrote a post sometime ago about how he could set a gauge up correctly with some thermocoupling doubler... (or maybe I'm having an XJS fantasy????)



Yes, that's right... I'd mentioned a gadget I've been using on my xj-s for many years. It clips onto the temperature sensor and it doubles the signal from it, so as to make it read 'twice as much' on the gauge.

I'd fitted it after I was puzzled why the gauge had read low, and only got to 'N' when the engine was boiling over.

Tested the transmitter for the temp gauge,at 8 to 10 C it measured 1500 ohms.

That's probably the right value for '8-10 degC'. I'd expect it to be about 15-20 times the 88 degC value.

The temp sensor is a 'NTC semiconductor', these have a moreorless exponential response. I wouldn't be suprised if the temp sensor was built using one of these:
http://www.thermistor.com/pdf/curves-z-y-t-w.pdf