Temperature Gauge incorrectly showing overheating

[Bahtatboy]

1973 +2S, recently refurbished.
Within about 5 mintues of start up from cold, the temp gauge is at its top limit, but the engine and cooling system show no sign of overheating. Today's runs were only the 4th and 5th since the car was delivered; there is only 50 miles on the rebuilt engine.
On today's first run, I stopped and investigated after about 5 minutes from start up (with gentle driving - still running in), and even though the temp gauge was in the red, I could comfortably place my hand on the block, head and radiator, and the water was at about 70C in the top of the radiator (measured with a cooking themometer). So it seems the thermostat is working. Checked the connection at the temperature sensor, and it was good.
On the second run today, of about 20 minutes, again the temp gauge was in the red after a few minutes, but again no signs or symptoms of overheating -- no steam, no hot smell, engine remained tractable and smooth.
Both the temp and fuel gauges rise slowly after turning the ignition on following a hot stop, indicating the presence of a voltage stabiliser (which I haven't been able to locate yet). The petrol gauge might be reading high, but I'm not sure.
Any thoughts or suggestions will be appreciated.

[mbell]

I would pull the thermostat and boil test it to be sure its good.

After that your looking at electrical issue with sender/gauge or regulator. Sender resistance should drop with heat, there likely values on the forum that map its resistance to certain temperatures.

From memory my 10v regulator is mounted to the back of the dash in the area below the speedo/rev counter, need to confirm its output is 10v, modern solid state ones are easily available to replace it.

Testing of the gauge would likely need a variable resistor to replace the temp sender to test it operation against the expected range of the sender.

[Lotus 50]

Sending unit!

[Billmack]

Both gauges are 10 volt voltmeters with damping for the needles. If both read high it's the stabilizer shorted if only the temp it's likely that the sensor in the head has gone bad. Does it read cold when its cold? Not sure where the stabilizer is. Often attached to the Bach of speedo or teach. Rectangular piece about 11/4 by 3/4 by 3/8 has two pairs of spade connectors one male one female. Likely fed by a dark green wire and feeding gauge with a light green wire. Can only be hooked up one way.

[Bahtatboy]

Thanks all. If I decide to replace the sender (sensor) unit, where's the best place to source it (in UK)?

[Bahtatboy]

Thanks all. If I decide to replace the sender (sensor) unit, where's the best place to source it (in UK)?

I've just spoken to the company which did the rebuild (or part of it), and they understand that there are two types of sendor units, and it seems possible that I have the wrong one installed. Before I remove it, does anyone know if it's possible to distinguish one from the other, and if so, how?

[alan.barker]

If you fit a new "Voltage Stabiliser" which are cheap you will have a good base to go from.
Many times they are screwed to the back of the Speedo which acts as the Earth
If it is just dangling around it is not Earthed could be the problem
Alan

[Bahtatboy]

If you fit a new "Voltage Stabiliser" which are cheap you will have a good base to go from.
Many times they are screwed to the back of the Speedo which acts as the Earth
If it is just dangling around it is not Earthed could be the problem
Alan

Thanks. Had a quick look to see if there is one, but couldn't find it (according to the manual it should be located close to and earthed to the speedo). Apparently solid-state versions are available -- do you know where I could get one if that's what I need?

[alan.barker]

SJSPORTSCARS for new Voltage Stabiliser under +2 parts. Please remember that the fixing bracket needs an Earth to it.
Have fun
Alan

[Bahtatboy]

SJSPORTSCARS for new Voltage Stabiliser under +2 parts. Please remember that the fixing bracket needs an Earth to it.
Have fun
Alan

Thanks

[Billmack]

Identifying smiths/Jaeger senders can be done by the color of the plastic insulator on the sender in my experience. That being said most of the experience is on bmc/ Leyland cars. Same maker for the gauges so probably similar coding.

[alan.barker]

If the Voltage Stabiliser is not Earthed correctly you will get high readings. Because the Gauges will get 12 volts instead of 10 volts
Alan

[Billmack]

A quick check is to check voltage at light green wire feeding the gauge. If 10 volts alls well. If more there's your problem. Mr Barker is right in that if that piece is not grounded(earthed) it will not work.

[Hawksfield]

Hi Bahtatboy

See my post with the same problem as you


viewtopic.php?f=39&t=45645

Good Luck

[Bahtatboy]

Hi Bahtatboy

See my post with the same problem as you


viewtopic.php?f=39&t=45645

Good Luck

Thanks