Hello folks!
I bought my first Jag on Saturday, so obviously here I am with my first technical question. It's a 2002 4.0 V8.

When you start the engine the engine fan comes on straight away, and the temperature gauge drops onto the needle. Turn the engine off and turn the ignition back on and the gauge works as normal.

Obviously having the fan on all the time is not ideal, and the idea of not having a temperature gauge with a V8 engine is pretty terrifying!

Does anyone have any idea what I could check before I take it to a garage?

 

Does the fan run when the aircon is switched off? It should run all the time that AC is on

 

Not sure what this means.

Check the coolant level and monitor it for gradual loss.

 

It does.

It means it goes back to zero.

There's no problem with the temperature of the car - I've checked it and it doesn't get hot.

 

Also check divas bottle for minor pin hole leaks, very common problem overlooked on these S Types….it was causing my gauge to go wacky.

 

meant to say DIgas not Divas, lol

 

What's a digas bottle?

 

Digas bottle is actually the coolant reservoir bottle….it seems to be what all the bulletins call it….Its basically a common problem on the S type and Lincoln LS. And you don't really know its leaking until you pull it out… if you google "s type digas bottle leak" you will probably come up with most of the stuff i saw…originally my mechanic thought that was nuts…and that it couldn't effect the temp gauge…so we changed coolant sensor, and even the plastic pipe that ors into…but that was a waste of money….pulled the reservoir bottle and you could then see the tiny pin hole leak…. you have to also remove the support bar that goes across the back of engine compartment to pull it out…soak the bolts for that bar with penetrating oil a day or two before because the part were they come through on the bottom, (above front wheels) are exposed to everything that gets kicked up into your front wheel wells

 

Thanks for all the replies so far - I've pulled the ODB code and it said:
"Engine Coolant Temperature Sensor - voltage high"

Anyone know where the ECT sensor is located? It might just need a wiggle.