Have only been taking the Jag out this winter when the weather is dry and above freezing.

Prior to a big roadtrip this weekend, checked coolant, oil, and tire pressure, all in spec.

During the first leg, a 2.5 hour highway run Thursday night, dash Temp gauge never got much above the left side C marking. Car was idling at about 1200 cold, then 850 when stopped about 20 minutes into the drive. Noticed I was getting no warm air through the center vents even at max heat setting, but felt heat on my feet. Fans work fine.

At my destination, shut the car off after letting it idle a bit, turned on ignition and now Temp gauge needle was just touching the N. Started the car, the needle started moving slowly back down to a little below N.

Second leg was a four hour highway run Friday, same thing happened. Needle just above C the whole way, no heat through center vent, Temp gauge needle moved up near N.when car shut down and then restarted.

On the final four hour return leg, same thing again EXCEPT about halfway through the drive, the heat started working properly. That is, I set a temperature and it was maintained, coming through the center vent.

Neither the Manual or AC button was on at any time.

Any idea what I am dealing with here?

 

It’s either your thermostat, coolant temp sensor, or the coolant temp sender.

In that order.

Id replace the first two for sure. Not expensive, and easy to do.

what model year and engine?

 

As Vee has mentioned, it possibly sounds like a stuck open thermostat.

The temperature transmitter is the sensor that sends the signal to the gauge. On your V12, this is located in the LH water rail. The CTS doesn't send a signal to the gauge. The CTS is located in the RH water rail.

Do remember that the face-level centre vents on a late XJS operate quite differently to many aircon systems. You should not use the face-level centre vents as an indication of whether the car is heating up properly. If you read the owners handbook, you'll understand how those face-level centre vents work. They are NOT designed to flow "hot" air. See the thread here for a description of how they work:

No hot air in central and demist vent + Strange vacuum hose question - Jaguar Forums - Jaguar Enthusiasts Forum

Hope that helps

Paul

 

Hi inertion

Maybe this will help



Coolant Temperature SENSOR Located on 'B' Bank (near the Oil Filler) XJS V12



Coolant Temperature SENDER Located on 'A' Bank (To the Gauge in the Car) XJS V12

 

Thanks for all the quick and detailed information.

Everything has been behaving normally since I returned from my trip, temperature gauge, cabin heat, etc. Thinking that whatever was stuck - thermostat, sensor or sender - got unstuck.

Have to check if the 'stats were changed when I first serviced the car upon purchase about a year ago, if not, probably a good idea to do them before the warmer weather arrives.