6 replies to this topic

[Dartmoor Paul]

I have an early Smiths magnetic type temperature gauge fitted in our Mini.  This is the sort that does not use the voltage stabiliser.  It has the correct early type sender unit fitted.  However it is tending to read a high temperature once the engine gets up to temperature.  The engine does not appear to be running too hot, so I wondered whether it is possible to adjust the gauge so that it reads slightly lower.  I suspect that this could be due to using the 82 or 88 degree thermostat rather than the earlier 75 degree item.

The photos show it in all its glory!

Attached Files

•  DSCN6948.JPG   45.77K   7 downloads
•  DSCN6951.JPG   42.85K   5 downloads
•  DSCN6946.JPG   63.9K   5 downloads

Edited by Dartmoor Paul, 23 August 2015 - 08:03 AM.

[dklawson]

My goodness that is rare.  Congratulations on having both a working early gauge and sending unit.

 

You CAN calibrate the gauge and sender to read better.  Rather than go into all the details here, please visit the link below to the MGA Guru web site.  The link is to the pages devoted to the magnetic fuel gauge, not temperature gauge.  Regardless, the gauges function the same and Barney (the website owner) has a section devoted to calibrating these early gauges. 

 

I cannot tell you what the resistance range of the early temp sender will be so you may need to remove the sender, connect a multimeter across its threads and spade terminal, and place the sender in a pot of boiling water along with a thermometer.  Cut the heat off and record the temperature and resistance every few minutes to develop a curve for the sending unit.  You will then be able to use that information to calibrate your temperature gauge using the methods shown on the MGA Guru site.  

 

The link starts by explaining how the magnetic gauge works, then using the forward/reverse arrows at the bottom of the page you will reach the calibration pages.

 

MGA Guru Fuel Gauge Link

[carbon]

If you're using a later type thermostat, then a late type sender may bring it back to the correct reading?

[Dartmoor Paul]

Thanks for some really useful information.  I'll study the link that you've provided and see how I get on.

[Dartmoor Paul]

I've fitted a variable resistor in line with the supply from the temperature sender.  By adjusting it down to about 3 ohms the gauge is now reading correctly.  I've road tested and all now appears to be correct.

[dklawson]

If I may offer a suggestion.

 

You used a variable resistor to find the 3 Ohm value.  That's great for experimental work.  Most potentiometers are not designed to handle more than a few milliamps for prolonged periods of time (wire wound potentiometers will be rated higher/longer).  So... I would carefully measure the resistance of the adjusted potentiometer and buy fixed 1/2 or 1 Watt resistors of the same resistance value and use them instead of the potentiometer.  They will handle the continuous current longer.

[Dartmoor Paul]

Good idea ... thank you.