ever since I purchased my 99 Vanden Plas non turbo with 120,000 miles, I have been plagued with a problem with my temp gauge . When driving , the temp gauge would behave normally but once I shutdown the car , sometimes when I restarted the engine , the temp gauge would stay at the temperature reading that it was at when the engine was turned off. As a result , the temp gauge very often would peg out . No codes are ever thrown and there doesn’t seem to be any effect on the engine . Sometimes when I disconnect the ground on the battery , the gauge goes back to normal and seems to work fine until the car is shut off again . I just replaced the thermostat along with the housing and the thermostat sensor but the gauge is still reading all over the place . The car has never set off the Red temp warning light , but yesterday it did set off the coolent level warning on the dash . But once I restarted the Jag the warning cleared itself and after checking the coolant level it was about where it should be . Because of the high mileage , and not having any records of previous maintenance, I have replaced the tensioners , the timing chains , the water pump , the thermostat and thermostat housing , brakes , rotors and new shocks ( front and rear ) I realize most of the maintenance has no effect on the temperature readings but I was trying to give you an adequate picture of where I am at with the vehicle . I hope someone can shed a light on my problem , because the nearest Jaguar dealership is over 50 miles from me . This is my first time using the forum so I hope I used it correctly.

 

You could try replacing the temperature sensor if you have not done that already.

 

Thank you for the suggestion but that was just replaced . I was confident that that might be the problem too , but apparently not ,

 

If the needle is staying put when you switch off then that's a not problem with the sensor, it's a problem with the gauge needle or more precisely the needle drive.

The gauge is actually a stepping motor (ditto the fuel gauge) and is driven in small steps by 'up' and 'down' pulses generated by software in the instrument module. When you switch off the motors/needles are driven down to the zero position. When you switch on both gauges recalibrate by initially driving down below the zero point until the hit the mechanical limit (trying to drive even lower); they then drive up the correct number of steps for whatever the current reading is.

If the needle sticks and can't drive back to zero when the ignition is switched off, or on, then when the 'up' pulses are applied it moves up from the sticking point to an erroneously high value.

 

If you want to be sure of the temperature, both my readers will tell you the current temperature.
I am having a somewhat similar issue with my 04's fuel gauge.
Just drops to empty & the light comes on, then returns to normal.
Guessing my issue is at its fuel pump connection.
Will need to pull the rear seat to check things out.
But it works most of the time, i know it's not empty, & i'm lazy.

 

[QUOTE=Partick the Cat;2081635]If the needle is staying put when you switch off then that's a not problem with the sensor, it's a problem with the gauge needle or more precisely the needle drive.

The gauge is actually a stepping motor (ditto the fuel gauge) and is driven in small steps by 'up' and 'down' pulses generated by software in the instrument module. When you switch off the motors/needles are driven down to the zero position. When you switch on both gauges recalibrate by initially driving down below the zero point until the hit the mechanical limit (trying to drive even lower); they then drive up the correct number of steps for whatever the current reading is.

If the needle sticks and can't drive back to zero when the ignition is switched off, or on, then when the 'up' pulses are applied it moves up from the sticking point to an erroneously high value.
Patrick , that is exactly what seems to be happening !!!! Do you have any idea what it will take to correct the problem . I’ve searched the internet but no luck . I assume ( and we all know what happens when you ASSUME ) that, even though the gauge is malfunctioning , the Red overheating warning light would come on if it was actually overheating !!! My mechanic let the car run for quite some time while hooked up to his temperature gauge and it showed normal running temperatures !!! Could driving the car like this be harmful to the engine ??? The problem has never set off any codes .Thank you so much for your help !!! I love the car and would really like to keep it , so I am really trying to kill all the gremlins, but my knowledge of these fine cars is extremely limited

 

Dan

Sorry, no ideas really, it's never actually happened to me (yet !) so I've never needed to address the prob. I just remember others posting up about it but I can't remember who they were.

Dave (in wet Gloucestershire)

(Partick's the car's mascot, as in the profile pic).

EDIT: Try using the search function for this subforum (not the one for just this thread) and search on a combination of
'temperature', 'gauge' 'needle' and 'sticking' or things like that.