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New to us 1987 XJ6 III 4.2 Sedan. (also have a 1974 XJ6 II)
I think I have read everything on the subject that I can find. Getting erratic readings from the cabin gauge. Starts out low, moves to the midpoint where it stays for a while, but then it moves very rapidly through the green and maxes out. Sometimes it bounces quickly from the midpoint to Max. Turn off the car and restart gauge will read slightly below green, as the car is already warm, but then repeats its erratic behavior. Have not hit it with an infrared to confirm normal operating temperature but will this evening. I do not think the car is overheating. Have replaced the single spade sensor/switch attached to the green wire. Same behavior. Unplug the green wire and the gauge is at zero. Ground the green wire and the gauge is at Max. So I think the gauge is okay.
Must be the wire right? Appears to travel down the front passenger side of the engine and then goes somewhere. Are there connections along the way? Would appreciate some insights on where I can check for a break. Part of the wire seems to have a speed connection to a small bulbous connector on oil pan or block? I suppose I can run a wire directly from the sending unit through the speedometer hole and attach it to the gauge to confirm.
Also have wiper issues but that's for another thread! Everything else works.
Did a little more investigation tonight. Car is definitely not overheating. 65-70C whether gauge is on normal or pegged. Weird even if sensor disconnected gauge moves a little, still under 50 when key is turned on. how is that possible. On my test run same experience: moves up slowly to 90 hovers there for about 8 minutes then starts to climb quickly within seconds to the high green then pegs it self.
New to us 1987 XJ6 III 4.2 Sedan. (also have a 1974 XJ6 II)
I think I have read everything on the subject that I can find. Getting erratic readings from the cabin gauge. Starts out low, moves to the midpoint where it stays for a while, but then it moves very rapidly through the green and maxes out. Sometimes it bounces quickly from the midpoint to Max. Turn off the car and restart gauge will read slightly below green, as the car is already warm, but then repeats its erratic behavior. Have not hit it with an infrared to confirm normal operating temperature but will this evening. I do not think the car is overheating. Have replaced the single spade sensor/switch attached to the green wire. Same behavior. Unplug the green wire and the gauge is at zero. Ground the green wire and the gauge is at Max. So I think the gauge is okay.
Must be the wire right? Appears to travel down the front passenger side of the engine and then goes somewhere. Are there connections along the way? Would appreciate some insights on where I can check for a break. Part of the wire seems to have a speed connection to a small bulbous connector on oil pan or block? I suppose I can run a wire directly from the sending unit through the speedometer hole and attach it to the gauge to confirm.
Also have wiper issues but that's for another thread! Everything else works.
Thank you for your anticipated assistance
Hanick
I suppose I can run a wire directly from the sending unit through the speedometer hole and attach it to the gauge to confirm.
I think this is the best and fastest way to rule out the gauge and sender. I wouldn't even run it through the speedo hole, just attach to sender, run a length of wire out under the bonnet, into the cabin through the door weather stripping and then remove the speedo or tach and replace the exisiting gauge wire with your test wire. Take a short drive and see what the gauge does. If everything works as designed, then you can decide on your threshold to pain and run a new wire properly.
Dave,
I ran a separate line from the sender to the gauge with the same behavior. Turn the key to run with the wire disconnected and the gauge moves slightly, why is that?
Start car gauge moves up, hovers at the 90 midpoint then, fluctuates in the green and rapidly moves up and maxes out. all within a minute or less. car is not overheating. Maybe my new sender is bad? Unplug gauge it zeros out, ground it and it maxes out. Could I have a bad gauge?
If you've replaced the sender in the engine block and tested with a new wire from the sender to the gauge, you have pretty much ruled out 2 of the 3 elements in the circuit. Looking back at the pictures I took when my dash was out, it appears that the metal frame of the dash is grounded and the clamping pieces that secure the gauges may complete the circuit through contact with the dash. Try wiggling the gauge or tightening the nuts on the clamping pieces. This thought is being thrown at the wall and might not stick at all, beyond that, the gauge would be suspect.
Do not feel alone. My quote skill is non existant/
Tme to review the Jaguar schematic S57. Immensely helpful...
Sensors a re a variable resistance device. Repond to temperature in respect the tmp guage.
Rmove the wire and touch to geound. If intact, it shl cause the guage to go to full on hot!!!
Teh other side of the cicuit is from the igntion switch. wonlky switch>? Wonky wires in the engine bay as doug suggests, a good place to staert One ithe wigglem test. Any change in numbers???
The temp gauge in my '87 often sits dead on 0 when I start the car up, and will not come off that number.
The fix? I thump it once on the glass (plastic?) with a fingernail. It wakes up and gives me no problems the rest of the drive.
The speedo in my '89 XJS also likes to peg itself to 80 mph and stick there. A thump or two on the plastic cover tends to fix it, as well.
I'm betting either the ground for that particular circuit, or something internal to the gauge itself (I've had many gauges fail in cars once they hit the 30-40 year-old mark).
I'm just glad I can still "fix" mine with a thump. Very cost-effective.
The gauges do need to be grounded to work properly. I would try running an extra ground wire from the gauge case to vehicle chassis and see if that makes it behave properly.I have had similar problems in other cars due to poor ground path the the gauge.
Coolant Temperature Gauge Wiring 1987 XJ6 III
