Hi there,

I have looked on here but can find no answer to my question. My temp gauge has suddenly stopped working - is this a major cause for concern ? should I not use the car. Any advice would be much appreciated.

 

I've moved your question from General Tech Help to MKI / MKII S type 240 340 & Daimler forum because you really need advice from members here with the same model.

Jaguar don't have too good a reputation for reliable temperature gauges. Later models like mine don't even have one!

Graham

 

As I recall, there is a small thermistor screwed into the water rail on the inlet manifold somewhere. As the temperature rises the resistance reduces allowing more amps to flow. The temperature gauge is therefore an ammeter, but calibrated in degrees C. I think there is also a voltage device somewhere to provide a fixed reference voltage.

First check will be to make sure you have a voltage at the thermistor. Then you need to check the thermistor itself for resistance, easily done as it lets the current go to ground on the manifold. If the thing is open circuit, then you have a duff thermistor.

 

With out checking, there is also this quirky voltage regulator that fails as well.
It's located inside the car on the fold down electrical panel.

 

The MK2 gauges are calibrated to run at 10V, if the thermistor is open circuit you should have 10V at the terminal if negative ground and 0V if it is positive ground and open circuit. You can short the lead to ground and the gauge should show "boiling" , if not check input voltage to the guage and regulator as Jeff said.

You can get a solid state regulator from cool cat in the US to replace the old one for better accuracy.

 

also check for the Captain Obvious- loose/missing connections, poor grounding to the chassis.

https://www.google.com.au/imgres?img...act=mrc&uact=8

 

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Replace the sensor on the the inlet water rail & check all wiring. That sensor commonly fails. Rubbish aftermarket parts.

 

To answer the second part of your question I personally would not drive a Mk2 without a working water temp gauge. After the oil pressure it is the most important instrument.

 

And sensors tend to fail reading low. Wiring problems to the gauge can make it read high.
Google 'a gentleman's guide to smiths gauges' for complete info.

 

Joseph Lucas no longer exists. Lucas today is merely a brand. I have five failed temp sensors. I'm a Magpie ~ they should be in the trash.

 

The Lucas trademark belongs to ZF and is licensed out to others. The remnant pieces of the business belong to more companies than you can count. Rolls-Royce have what may have been the best bit, with whom they had long collaborated, the aero-engine control division.

Lucas bought Smith's automotive instrument division in the 1980s, though one might have imagined it was much earlier. In fact, the ownership was brief as that division was subject of an employee buy out. Thanks to that, the business is still going and produces Smith's classic instruments (not to be confused with the many copies). The rest of Smith's Industries is also still in existence but has moved into control systems, sensors, aerospace electronics and other non-automotive areas.

 

I have given up being a "Magpie" with old electric oil and temperature sensors. I 'bin" them straightaway.
I have had oil pressure sensors leaks and failures in a number of Jags and in one case a blowout in my X300 which emptied the sump and by sheer luck I pulled up at a rest stop and found it before any damage was done.
The most reliable sensors are in my MK1 which has capillary gauge systems for oil and temperature.
NOTE for MK1 owners. Do replace the flex hose piece in the oil capillary tube if you can't determine its age. I had one "blow" many years ago.

 

anyone know where i can get a new temp sensor (the one the threads into the thermostat housing, or near it) for my '67 3,4l mk2? thanks, i've lost confidence in mine. and yes, i've done my due-diligence, scouring the net for an hour and finding many for jags, many look the same as mine, but could be calibrated differently, especially if they're advertised for an E-type or an MGB, or a Mini, or an XJ or XJS, etc., etc., etc.

the current one has a spade connector, but i'm not so sure it's right, as i said, i'm suspicious.

 

Mine came from SNG Barratt. It was damn expensive ~ About 50 GBP. I no longer find it listed. P/N C 15472 (Jaguar calls it an "element" feeding to the gauge)

 

Mine has a spade connector and so did my new harness.

Original on earlier engines.

 

https://www.sngbarratt.com/English/#...20%60C15472%60

I assume these are manufactured by the Wun Hung Lo Mfg. Co. (Directors, Sum Ting Wong & Ho Lee Fuc)?

 

Likely. It did not come up when I searched but I had filters on. The * would have ignored it.