Hi Marc, this from my FSM. Testing the sender - a semiconductor device - calls for a Smiths instrument tester. I expect none of us have one of those! Frank is on the right track. It should be possible to measure the resistance of the sender at room temperature and at boiling point (effectively nil on the gauge and full scale deflection). Theoretically using sample resistors (in place of the sender at the car) you should be able to make the gauge operate between nil and full scale. If your sender is good the nil and full scale resistances (measured as you boil up the sender) should match the sample resistors used in place if the sender. That’s what I would try. Paul.
Thank you Paul!
What book is that? Looks like it contains a lot of interesting information.
/Marc
Hi Marc, it’s the genuine Jaguar Workshop Manual. Paul.
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Directly between the sensor connector and ground, Mark - wire disconnected. The resistance readings may jog someone’s memory…
And my gauge has temp numbers, not ‘normal/hot’ - hence the question.
Frank
xj6 85 Sov Europe (UK/NZ)
Marc,
at this point any discussion isn’t worth the 12 EUR for a new sender. Your original is non-functional and arguments about the quality of new ones are moot as you won’t be able to fix the original one.
It won’t be the voltage regulator unless your fuel guage is acting up similarly.
Last cross check is to ground the sender and check whether the guage needle pegs out right.
Swapping the sender is a 20mins job.
Good luck and keep us posted
Jochen
75 XJ6L 4.2 auto (UK spec)
1 Like
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Two minutes, Jochen, with the correct sender - unless you have along walk to the car…
With the engine cold, there is no need to lower the coolant level…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thanks everyone!
Since the sender on the S2 is located upside down under the water rail I have received some words of caution.
I was told by a trusted expert to be very careful when removing the sender since it is possible that crud has been collected in the cavity just above the sender and that the crud could damage the threads when the senders was withdrawn.
Anyone with experience of this?
/Marc
Hi Marc just completed this task with none of the issues that you mention. Main thing is to cover the distributor with a plastic bag to avoid coolant getting into the electrics.
Thank you. Good to hear.
/Marc
Hello!
An update on the temperature sensor issues. I replaced the temperature sender and everything now seems to work as intended. The temperature gauge now points to “Cold” when the motor is cold and stabilizes somewhere between “o” and “r” in “normal” when the engine has reached operating temperature.
Thank you all for your advise and support.
/Marc
1 Like
Thanks Marc,
for the update! Congratulations for a job well done. Your update will show others following you that - fortunately - sometimes problems are really easy to identify and remedy.
Unfortunately, temp sensors don’t have a clear failure mode. Many times they cause less obvious misrepresentations of the respective guages and a high risk of misguided concern, outright panic and $$$ spent for no valid cause.
One question left: Did you encounter a flood of crud when you removed the sender? - Frankly, I wouldn’t know why a lot of crud should accumulate at a point where to my understanding the water flow is quite intensive, and why even some crud pouring out would be able to damage the thread … sure enough you’d feel any residue in the way when fixing the new sender.
Enjoy your car
Jochen
75 XJ6L 4.2 auto (UK spec)
Hello Jochen!
Thank you.
I wouldn’t call it a flood, but yes, the coolant that came out when I removed the sensor was rather brown. There is a cavity/groove in the water rail just above the coolant sensor where i guess crud can accumulate.
I had no issues removing the sensor. It came loose rather easy and I could then unscrew it by hand. Just to make sure, I cleaned the threads a bit with a cloth, let them dry over night and even used some compressed air to remove any remaining dirt before fitting the new sensor.
/Marc
1 Like
Question: Is the coolant temp sender for the gauge different than the one for the FI system on my 1975 XJ12C? I see the two pole sender on the B bank just behind the thermostat. What is the single pole sender behind that?
Completely different. The one for the gauge provides a modulated ground for the gauge, I think. The CTS for the EFI is a variable resistance in a 5V circuit.
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‘Averaging’ is pointless for verifying dash gauge reading, Mark - the only relevant temp is from the water rail at the base of the sensor. This is the temperature picked up by the sensor and works the gauge…
One question; are all the senders of the same type? The gauge/sender is a ‘matched pair’ - and different gauge/sensors may not be compatible.
Adding a fixed resistor is not the correct, or final, solution. It is OK for getting the correct reading at one specific temp - but will be incorrect at others. However, a faulty wire may also introduce a resistance - which will cause the gauge to misread in the same way…
If you want to pursue this problem; use a variable resistor between wire and ground. Measure temp at rail with the IR - and adjust the resistance for the relevant gauge reading. Measure that resistance and compare with the sensor’s resistance. Repeat as the mood takes you.
What this actually does is to compare the temp ‘curve’ of the sensor compared to the what resistance the gauge wants for correct reading. If they differ; the sensor does not match the gauge - or there is something wrong with the gauge itself…
All this is sort of academic; if you sort of have an idea of what gauge reading relates to what engine temp - the main value of the gauge is mainly to supervise rise and fall of engine temps…
Frank
xj6 85 Sov Europe (UK/NZ)
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Possibly related to the EGR system, if you have one.
That position on the water rail was used for a wide variety of different thermal switches depending on year, spec, and original market. I tried doing a little research in the old parts catalogs to narrow things don but, as luck would have it, the image was so blurry I couldn’t make heads nor tails.
Cheers
DD
David,
I recommend that you post a picture of the part that you are asking about.
Paul
Mark,
why did you withdraw? You can easily amend the text, once you find you
got something terribly wrong …
As for your first point - my car is a 75 LWB car. At a certain point of
production it seems SII SWB were totally cancelled. Maybe it had to do
with the practical sale of the coupés, because after that point of time
the catalogues only specified “XJ6L” and “XJ6C”. So, all in all a SII
SWB car must be pretty rare.
As for your second point: the closed circuit test effectively only
states the condition of the guage. It is quite obvious that limited
obstructions by poor connections are not revealed.
Also: it always was my impression that the needle is supposed to go
twelve o’clock at considerably more than t-stat temp. At t-stat temp
(usually 82 or 88°C the needle is a needle width (88°C) or two (82°C)
left from northward. I was happy that after trying two new 88°C sensors,
the second of which proved to work correctly in a hot water bath, now my
needle finds itself at the “n” of “normal” warmed up under normal
conditions and will rise to the “r” with serious work (constantly +3000
RPM) or ambient temps. With very high ambient temps and lack of air flow
caused by city driving or autobahn jams it’ll rise to the “a”.
In your case I’d doubt whether the entire wire is shot. Maybe it’s only
the connectors. Besides the spade connectors at the sender and the guage
there should be at least another two plugs and sockets as per the wiring
diagram. Before tossing out the wire I’d go after these first.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
Why did I withdrawal? For the same reason why I haven’t been on the forum for nearly 6 months, posted a Video on YouTube, or even touch any of my Jags since. It will be six months this coming 23rd of November. My son, my best friend committed suicide by way of a bullet to the head. I was working on my Jag Mods video out in the garage when he left me a video text message. The phone was in the house charging.
I was waiting for him to show up after work for a out weekly pizza, movie, and Baskin Robbins (ice cream shop in the US) stop on the way home. I missed the video (by 15 minutes) of him telling me good bye and by the time I got the video message he would be gone? At the time, I thought Gone where FFS! We have a date! Then it dawned on me; Oh My God!! NO!!
I tracked him down via his cell phone. By the time I got there. the park was swarming with police, and a white van. The last time I saw my son he was covered with a blanket his feet dangling off the end of the stretcher. Shoe laces untied as usual.
My self-centered passion for making clapped out cars new again cost me something more dear to me than life itself. So needless to say, It’s been really hard for me to look any of my jags, or anything to do with a Jag without reliving the guilt for not being there when my son needed me most. I write this message with tears streaming down my face reliving the worst day of my life. For those who are wondering why? As if it really makes a difference, it was over a breakup with his girlfriend. A girl FFS! Then my dog and my pet Rat died – old age, but still my Son, Trent, loved these little critters as much as I do or did…
My Son, and our beloved pets sit on a shelf next to their pictures like a trinket. I’m withdrawing my post because I’m not ready.
Mark
I’m having trouble coming up with anything to write. This hits hard.
I can not imagine how the last six months must have felt for you.
I looked you up a few weeks ago but when I had asked before you were fine then. Wish you were now.
I‘m really sorry Mark.
I look forward to having you back when you feel better… thanks for writing. Wish there was anything we could do for you. Take your time.
Don’t give up.
David