Coolant level is OK, no leaking, coolant temperature on gauge is OK. Before light is on cca 2 minutes after start, now all the time... I change coolant temperature sensor, same problem... any idea?

 

If you mean this warning light



It's for low coolant level.

The sensor is located in overflow tank on left

 

It's V12 5.3 - 1983 H.E.

 

Paul, is this sensor also on 1983 ? I'm checking overflow tank on left , but can't see nothing....

 

Item #2 in this picture

Expansion Tank and Water Pipes-5.3 Litre - Parts For XJS from (V)139052 to (V)179736 | Jaguar Classic Parts UK

However, I think some earlier cars have a radiator mounted switch....but I can't swear to it

Cheers
DD

 

A good plan to include these details in your signature, that way they appear automatically.
The low coolant level sensor is on the header tank, it is nothing to do with the coolant TEMP sensor. The level sensor works by illuminating when there is NO current passing through it to earth via the coolant fluid itself. The sensor itself is a push fit into a rubber bung, which bung is itself a push fit into the tank body. So to test the sensor circuit, carefully pull the sensor probe out of the flat side of the header tank. Seal the bung with a suitable small bolt into the bung or similar to stop the leak. Once out, ignition on and car running, the sensor should have NO current possible to earth and the light on the dash should be on. Earth the sensor to the engine and the light should go out.


If it does NOT go out, then the circuit has probably earthed somewhere because of a broken wire insulator or similar, or the relay that controls the circuit or the sensor is faulty, etc etc.
Greg

 

nothing there. my XJs don't have coolant level sensor in EXPANSION TANK (no wires there)

 

Hi Zarnca

This was the Coolant Sensor, that 'Greg' was talking about but make sure the connection is clean and not covered in paint like this one.

Maybe you have just got a dirty connection.

 

No, my XJs don't have coolant level sensor here. My VIN is 112222 - expansion tank is without hole.
system with sensor:
XJS from (V)139052 to (V)179736
XJS from (V)179737 to (V)226645

 

The Great Palm's book says:


"COOLANT LEVEL SENSOR: On earlycars, it’s at the front right side of the radiator, where it’s very hard tofind unless you have the hood off. Sometime in the early 80’s, it was relocated to the header tank, whereit’s a lot easier to get to. If you havea car with the earlier sensor location, at a convenient opportunity you shouldrelocate the sensor to the header tank. Simply drill a hole in the header tank about 3” above the bottom and insertthe existing sensor with a new grommet, and find some way to seal the hole inthe radiator.


This sensoris nothing more than a pin that makes electrical contact with the fluiditself. The resulting ohmage reading isprocessed by an electronic gadget, C42294, into an on/off signal to the dashindicator light. "
So have a look there and follow the same test I mentioned above.
Greg

 

YESSSS, I resolve this problem. I changed temperature sensor and transistor in control unit (in a black cylinder - transistor CD4011).... but nothing. Now I finally found coolant level sensor - On earlycars, it’s at the front right side of the radiator (secret location). Little bit a contact spray and mystery is gone. Thanks to all for helping.

 

Good work !


Cheers
DD

 

Glad you're fixed.
Excellent post from Greg (and My Kirby Palm book)

 

Also wanted to say welcome to Zarnca