Temperature gauge revisited

[vadas1]

I posted about my temperature gauge a while back. I have a Rover 3,9 EFI in my Stag. It runs great and using an infrared thermometer does not overheat. Yet within a few minutes of starting up the gauge goes straight into the red and past. I have a new Triumph temperature sender and temp gauge. A new voltage stabilizer and the fuel gauge works perfectly. I replaced the wire from the temp sender to the gauge bypassing the new wiring loom. Still does the same. The only thing left seems to be switching the temp input with the power input. If you look at the gauge the temp input is at 9:00 and the power in at 3:00. Should I switch them around? Any help would be greatly appreciated.

Ralph

[mjheathcote]

Fit a mechanical capillary gauge instead.
They do not lie and you can dunk the end in a pan of boiling water before fitting to ensure it is calibrated correctly.

[StagJonno]

Not sure what you mean re "temp input" and "power input"

As far as I'm aware, the only connections to the gauge are +10V from Voltage stabilser (light green), input from Temp sensor (green/ blue), plus a -ve and +12V for the illumination. Have you got a non-standard gauge?

Jonno

[vadas1]

Not sure what you mean re "temp input" and "power input"

As far as I'm aware, the only connections to the gauge are +10V from Voltage stabilser (light green), input from Temp sensor (green/ blue), plus a -ve and +12V for the illumination. Have you got a non-standard gauge?

Jonno

Completely standard Triumph gauge from robsport. Wondering whether switching the power in over to sender in side and sender where the power comes in. Probably try that tommorow as I am out of ideas why the gauge appears to be earthing somewhere with the latest wire switch.

[StagJonno]

Will be interested in your findings. As far as I know, the Temp gauge is a bi-metal type and is essentially a resistive element that heats up - heating of the bimetallic strip causes it to bend and move the pointer. The current flow (and therefore the heating effect) being controlled by the temp sensor which is a resistor whose resistance varies with temperature. The way the connections (+10V and Temp Sensor) are made shouldn't make any difference with a healthy gauge.

If your gauge is faulty with a short between the Temp Sensor input and the can, swapping the connections might result in putting a short circuit on the Voltage stabiliser, which could be damaging. Suggest you first, with the ignition off, disconnect both wires and then measure the resistance between the can and the Temp sensor input and then the can and the +10V input. On my one, which was working fine when removed, both of these are isolated from the can (ie indicating an infinite resistance). If yours isn't, then that's your problem and you'll need to replace/ repair. For reference, the resistance between the terminals on mine is ~65 ohms.

Jonno

[wilf]

Suspect a mismatch here between sender and gauge. Can't remember the precise specs for the various senders, but they do vary considerably.

[vadas1]

Will be interested in your findings. As far as I know, the Temp gauge is a bi-metal type and is essentially a resistive element that heats up - heating of the bimetallic strip causes it to bend and move the pointer. The current flow (and therefore the heating effect) being controlled by the temp sensor which is a resistor whose resistance varies with temperature. The way the connections (+10V and Temp Sensor) are made shouldn't make any difference with a healthy gauge.

If your gauge is faulty with a short between the Temp Sensor input and the can, swapping the connections might result in putting a short circuit on the Voltage stabiliser, which could be damaging. Suggest you first, with the ignition off, disconnect both wires and then measure the resistance between the can and the Temp sensor input and then the can and the +10V input. On my one, which was working fine when removed, both of these are isolated from the can (ie indicating an infinite resistance). If yours isn't, then that's your problem and you'll need to replace/ repair. For reference, the resistance between the terminals on mine is ~65 ohms.

Jonno

Thank you Jonno. I will try this. My brain is probably failing but what do you mean by "the can" ?
Cheers
Ralph

[vadas1]

Suspect a mismatch here between sender and gauge. Can't remember the precise specs for the various senders, but they do vary considerably.

I suspected that at first as well but now the sender is a Triumph unit as is the temp gauge. Both from Robsport and both brand new.
Cheers
Ralph

[wilf]

I think "the can" refers to the outer metal body of the gauge.


And if everything else checks out, the gauge is faulty.................

[StagJonno]

I think "the can" refers to the outer metal body of the gauge.


And if everything else checks out, the gauge is faulty.................

Thanks Wilf,

Yes, the can I was referring to is indead the metal case for the gauge. Only just found time to check in today.

Jonno

[vadas1]

Will be interested in your findings. As far as I know, the Temp gauge is a bi-metal type and is essentially a resistive element that heats up - heating of the bimetallic strip causes it to bend and move the pointer. The current flow (and therefore the heating effect) being controlled by the temp sensor which is a resistor whose resistance varies with temperature. The way the connections (+10V and Temp Sensor) are made shouldn't make any difference with a healthy gauge.

If your gauge is faulty with a short between the Temp Sensor input and the can, swapping the connections might result in putting a short circuit on the Voltage stabiliser, which could be damaging. Suggest you first, with the ignition off, disconnect both wires and then measure the resistance between the can and the Temp sensor input and then the can and the +10V input. On my one, which was working fine when removed, both of these are isolated from the can (ie indicating an infinite resistance). If yours isn't, then that's your problem and you'll need to replace/ repair. For reference, the resistance between the terminals on mine is ~65 ohms.

Jonno

I've done this and on both lines it shows infinite resistance. Resistance between the terminals is 63. Gauge takes about 4 to 5 mins to go past red from cold. 2 to 3 mins when warm. Completely stumped.

Cheers

Ralph

[StagJonno]

Ralph,

Understand your frustration - that's indicating no earth short circuit in your gauge (but doesn't of itself confirm integrity of the gauge, but makes one think that the sensor is the most likely culprit). I have a my old Temp sensor & gauge in stock that were working fine when I removed them (fitted a combined capilliary Temp & Oil gauge). I want to keep them so that the car can be returned to original, but would be prepared to lend them to you for a week so that you can do some substitution. If you want to do this, please PM your address details etc.

Jonno


Jonno

[vadas1]

Ralph,

Understand your frustration - that's indicating no earth short circuit in your gauge (but doesn't of itself confirm integrity of the gauge, but makes one think that the sensor is the most likely culprit). I have a my old Temp sensor & gauge in stock that were working fine when I removed them (fitted a combined capilliary Temp & Oil gauge). I want to keep them so that the car can be returned to original, but would be prepared to lend them to you for a week so that you can do some substitution. If you want to do this, please PM your address details etc.

Jonno


Jonno

That's a very kind offer Jonno. The sensor is brand new from Robsport. It is possible that it was a dud but I've managed to get hold of a mechanical temp gauge which will fit so I am going to go that route. Thank you again for your kind offer. The joys of British Leyland!
Best Wishes
Ralph

[StagJonno]

That's grand, Ralph,

You may need an adaptor extension to accept a capilliary as it's longer - I did. Think most of the usual suspects can supply.

Jonno