Thermostat housing removal

All of which means that the engine is running at the thermostat temp, Ian - confirming thermostat function, as it should…

You also need to measure the temp at the sensor - which is what the temp gauge is getting. The sensor just varies its resistance and indeed checking its resistance against another sensor as you propose - and swapping the two sensor may show something. The sensor and gauge fitted must be a matched pair - and two versions of both are available…

All ‘our’ gauges use ‘straight up’ to show 90C - about 11 o’clock at 80, so your needle in the ‘white’ section means that the sensor is mismatched to the gauge, or faulty. It’s all about instruments; the engine is running at the proper temp - all xk engines are created equal…:slight_smile:

xj6 85 Sov Europe (UK/NZ)


these IR thermometers are just great, aren’t they? Your engine couldn’t to any better than what you measured. Now leave that t-stat alone and take care of the sensor and/or the gauge.

I was fooled twice by a slowly failing sensor and I have made use of two otherwise identical (fuel) guages with a considerable difference in reading. Change the sensor and I bet you’ll be back in the game. The variance in guage reading is immaterial given you use the guage primarily to detect changes.

Good luck


75 XJ6L 4.2 auto (UK spec)

One way to check is to Ebay a $25 Digital water temp Gauge & Sender, you will likely need a thread adaptor for a few $.

I have done this to verify factory gauge.

You CANNOT tee a water temp sender, it MUST be fitted with its body immersed same place as original, or it will not be accurate

I may do this for my 420G, which has NORMAL, runs between R and L, even in ambient temps above 30C, but I would still like to know what those represent in actual degrees C

The one I was using suddenly became innacurate by about 15C, so I have fitted it against the engine block (of another vehicle) that has a red area of 112- 117C, as it has a red light that comes on at 100C (so actual 115C on engine block would activate warning light)

I also found this a bitch of a job, but only because I didn’t realise that the housing itself had a tiny crack through which water was leaking. After the fifth attempt to stop the leak with new gaskets and different sorts of sealant I finally thought to use a mirror to look underneath and see where the leak was coming from. I was lucky enough to be able to source a second-hand replacement housing at a very reasonable price from Ken Jenkins in Worksop (UK) which is a superb place. Fitted that and everything worked again. Parts like this are now getting hard to find, so I feel I was very lucky to find one. Moral of the story - metal can crack and leak, even though you might not expect it!