Series 3 XJ6 Temperature Gauge Graduations and Hot Running

Ok, I swear I read a thread about this before but for the life of me I can’t seem to find it. So I wanted to make sure I am reading the gauge correctly, the first graduation mark after 90C is 100C and the next one is 110C, right? I checked with an IR temp gun and it seems to be correct but I just wanted to make sure. FYI the reason the engine is running hot is a faulty aux cooling fan that I am fixing at the moment.



The green sector denotes ‘safe’ - from boiling, William; provided the system holds prescribed pressure. The coolant boiling point is then at some 120C - and the markings is as you describe.

As an aside; auxiliary fans are usually set to start at 95C - and the ‘main’ fan should nominally keep the engine temp a thermostat temps with a well working cooling system. It’s no the higher temp that is alarming - but a continuous rise…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

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Never done the test, but it seems so.
I have the 87°C thermostats and the gauge is always just below the 90° mark.
And my sender has the correct resistance to temperature values.

Is your car overheating on idle, cruising or both?

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When cruising around the neighborhood with the A/C off it stays around 95C and with the A/C on its closer to 100C. but after a drive sitting in the driveway with the A/C on it likes to creep up a little past 100C and stays there. When the aux fan was working it stayed rock steady at 90C without A/C and closer to 95C with A/C on. I am not super worried, I have a feeling when I fix the aux fan it will solve the problem!

Great thanks!

Yes i have had cars that like to go into nuclear meltdown, but this car was behaving just fine when the aux fan was working. staying at a steady 90C and occasionally going past that on a warm day with the A/C on. I suspect that I left the relay ground wire undone when I replaced the water pump, ever since the water pump job i had noticed the car ran a little warmer than before, but that was when it was cool outside, now that it is warm/hot it has made the problem much worse! Fingers crossed its just a forgotten ground and not a dead fan, or some cooling system fault!

In theory, and in all but extreme conditions, the engine temperature should never be more than the thermostat’s nominal rating.
The AC would put extra load and that’s why the Aux fan is called for.
To put your mind at rest, the best would be to compare your gauge readings with an IR thermometer. Both sender and gauge could be a bit off.

I, unfortunately, know that the gauge is correct as is the sender as I just replaced it and have verified multiple times with an IR gun that it is accurate to +/-1C. I am going to fix the Aux fan and I’m going to test the fan clutch as it seemed like it was not moving that much air at idle. The only other thing that it could be in my mind, is the new water pump. Maybe its not moving nearly as much water as it should. Although I doubt it.

True but don’t these cars run at 90C when they are “healthy”?

I would start with the fan clutch, then the radiator.

Yea, I have done some research on how to test them and it seems pretty simple and it’s pretty obvious when your viscous coupling in the fan has failed. Really hope its not a clogged radiator. I would prefer not to take the entire cooling system apart.


R&R’ing the radiator is one of the easiest jobs on these cars. And it’s something that should be done regularly, not on an as-needed basis – by the time you decide it’s needed, damage may have been done.

From my experience, if you hear it when you start the engine , then stops, then you hear it again when engine temp rises above 90°, it works ok.
When mine failed I couldn’t hear it at all.

Good to know! i’ll give it a try tomorrow

I heard my fan three times: once on a hot day, once when I drove without the main fan because the clutch had seized, and the other times the coolant was really low, the gauge ran way into the green and it really wasn’t good. If it shows ~88 warm on a cool day it shouldn’t exceed 95…maybe 100 running into traffic with the AC running. Something is up.
It shouldn’t run hot when rolling otherwise it is likely not the fan clutch, give the fan a spin. Resistance?

Alright, I was able to test the fan today and I have been flushing the coolant system at the same time (it was very brown and dirty). The fan seems to be operating, but doing the infamous “newspaper” test with a magazine I am able to stop the fan while it is at/above normal operating temp. Now it doesn’t stop super easily but with a fairly small amount of pressure I am able to completely stop the fan and when released it seems lethargic when it speeds back up again. This leads me to believe that the fan clutch is on deaths door, as I went for a drive and it got hot even faster this time.

The standard test is to give the fan a good twirl, William - if it spins on for more than half a turn; it’s a sign of clutch failure. However; travelling a speed; the ram effect renders the fan unimportant…

That engine temp varies a bit with load, and generally runs warmer at high ambient temp; it’s sort of ‘normal’ - sort of in reasonable health. Our jaguars were not overcooled, and coolant system deteriorates over time. But I would be concerned if an auxiliary fan was required - unless the weather is hot and the car stationary.

xj6 85 Sov Europe (UK/NZ)


I would do the radiator at the same time though, I am quite certain that it’s not in top shape.
I had an inoperative clutch for quite some time, but a good radiator, and temps were kept at bay except on slow driving at hot days.
The rule of thumb is that above 60 km/h neither the clutch fan, neither the electric fan do anything any more…
It’s a fairly easy job, and on plus will make the change of the clutch a much easier job.

When stone cold it does in fact spin for a little more than 1/2 a rotation, but strangely when hot (with the engine off obviously) it spins even more, more like a full rotation or 2.

To be honest this car mostly cruises on the 101 coast road which is just stop and go traffic at around 45mph max. the brief amount of time I had it on the freeway before trying to fix this problem yielded a nice and cool 90C or slightly below. I don’t think the radiator is bad, as sufficient airflow seems to keep the car nice and cool at 70mph (105-110 kph). when it gets hot is when the A/C is on max and is driven around my neighborhood which very hilly.

A detail that I forgot to mention is this car has been fully apart ie engine out for the paint job. which is when we checked the radiator and it seemed undamaged and in good condition. just needed a good cleaning. I am fairly certain that the radiator isn’t %100 good as new but I feel it is in good enough condition seeing as the car was behaving up until recently in regards to temperature.

I agree that a new or professionally cleaned and flow-tested used radiator would be ideal but Its a bit expensive to do at the moment for me and unless you can find a new radiator for less than $800-ish. Now if the problem persists even after a new fan clutch I will obviously be forced to get a new radiator.

Alright I somehow missed this but, does anyone have any experience with these cheap radiators from china sold through ebay? are they junk or “decent”. if its the latter I could justify replacing the radiator immediately if the clutch does not fix it.