Hi All

You might notice I don't log in to this forum often, but I do find lots of excellent answers here, so big thanks to all of the members who provide such good advice.

This time though I'm stumped so hope someone can help me out. Recently I've been getting a false overheating warning on my X-type (2001 3.0 litre sport auto). I've seen many people with similar problems, but each one seems to be different and mine looks different again.

The symptoms:
On longer journerys, after doing 50 miles or so the temperature guage will start to rise to the end stop and the red warning light comes on. If I stop and turn off the engine, wait 30 seconds and re-start the engine the guage returns to normal, the light goes out and I can make a bit of progress before it repeats itself. It can't possibly be a genuine overheat, the engine would never cool that quickly. Sometimes after a few cycles of false warning, stopping and restarting the engine it gets to the point where it won't happen again.

I have a bluetooth OBD connector in the car, so I can see engine temperature on my phone. When the needle on the console starts to rise on a false overheat, the temperature on the phone does not budge.

I've read some posts on this forum saying that voltage can be an issue on these cars and could be the cause of this fault, so yesterday I got my multimeter out and ran some checks. Before starting, with a cold engine, the battery was at ~11.8v (a bit low I know but the car doesn't get used much so figured that's the reason). It started without hesitation, and the volts at the battery posts went up to 15.1. After a while, once the engine was up to temperature, the volts dropped back to ~13.2. I think this is in line with what Jaguar say it should be, so charging is fine even if the battery is a bit low (battery is only 3 years old btw) and looks like battery cables probably are too.

So, I don't think that voltage is the cause of my problem, but happy to hear arguments to the contrary? Although I have noticed that the voltage reading on the OBD is about 1 volt lower than measured at the battery with a multimeter.

Other possible culprits include the fan control module so, once the car was up to normal temperature, I set the AC to max and had a look at the fans. Both were running fast so figure that the module is doing its job. Is there anything else I should look at there?

The coolant temperature sensor could be a problem. But if that was giving false readings wouldn't that show up via the OBD? The temperature I see there doesn't move in fault condition, however the OBD is giving me code P0116, "Concern with engine coolant temperature (ECT) sensor".

The other things I suspect could be problems are the ECU and the instrument cluster, but I'm not sure how I would test these.

I'm really unsure where to go next with this. Any advice would be appreciated.
Thank you for reading.