1989 XJS 12 , Lucas ignition vehicle . Temp guage climbs to just above the"N" , some times higher at times , but settles back above the "N". Does not change at higher speeds , when parked , and then restarted after 15 minutes or so , guage shows way above the "N", then come down just above the "N". System is full , no leaks or boil over . No leaves or debrit in the front of radiator. Just bought the vehicle , it's been sitting a while prior to my purchase .

Jaguar Sensor, XJ6, XJ8, XJS, XK8, S-TYPE, X-TYPE, XJ40 ...

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FITS: 1993-1994 6.0 XJ12 AND 1989-1993 V12 XJS FROM VIN 157118 ON, 1994-1996 6.0 V12 XJS FRONT DAMPER .... LNA1622AA - MAP SENSOR ... C42166-USED - USED SENSOR COOLANT TEMPERATURE FOR FUEL INJECTION

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Jaguar XJS Coolant Temperature Sensor - YouTube

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Working on the Jag and bringing it back from bad mechanics that have bad skills. If you do not know how to ...

air lock in the cooling system get a plastic bottle cut the bottom off turn upside down put on radiator filler and run engine cut full off water wait until all air bubbles stop then remove and put cap on see how that goes

Yes, if the Gauge continues to climb it is either the sensor or the Gauge

I would suggest having the engine temperature sensor and circuit checked, as well as your engine temperature guage. The guage is best checked with the use of a scan tool used by the dealer or a repair facility. If no signs of actual malfunction of the vehicle are present, you may just be throwing money at the car because of a false reading on your temperature guage. Some cooling systems require a specific filling procedure. If not done properly, air will be trapped in the system, causing similar issues to what you are experiencing. That would also cause loss of heat in the cabin, as well as overheating of the engine.

As soon as the temperature in the engine reachs the temperature of the thermostat rating i.e. 195 F or 95C, it opens. Then the temp. guage goes back to normal and the coolant heating in the engine begins again & the guage will even out after a number of thermostat openings. Make sure you retop off the the antifreeze after it has recicled a few time because of vapour lock etc. Good luck!

temperature sender unit top of engine cylinder head make sure its okay
and make sure wire going to it is not grounding
if it grounds or earths it will send the gauge up and down

First thing to do is replace the thermostat, and then do a test run.

The hoses may be collapsing, you may have to replace the radiator cap

make sure you cooling fan is coming on (this should when the temp guage starts to climb) and also make sure the temp sensor that turns it on/off is good. You could also have low coolant or bad thermostat (the wrong mix of coolant) or oher major mechanical issues but start with the fan and coolant level/mix

air con is broken