Chris Tyrrell TR6 Posted August 9, 2004 Report Share Posted August 9, 2004 Hi Guys. Does anyone know the temperature range of the Smiths temp gauge fitted to a CR series TR6? The gauge has been playing-up for a while and then last month stopped working altogether. I ruled out the sensor by checking the impedance when hot and hot. I stripped the gauge down to find that the needle was rubbing on the front bezel. I carefully straightened the needle and re-assembled. The needle now moves but never beyond half way. I removed the gauge again yesterday but couldn't see anything to suggest that the needle is still rubbing. If the gauge is showing the correct temperature then fine, I can stop worrying, but I would like to measure the temperature close to the sensor and compare it to the reading on the gauge. The car does get hot quite quickly and I'd like to keep an eye on the temperature. Many thanks. Chris. Quote Link to post Share on other sites
marvmul Posted August 9, 2004 Report Share Posted August 9, 2004 In general, the electrical T° gauges aren't very accurate, the mechanical one's of the sidescreen cars are better. The voltage stabiliser(behind the dashboard) is essential for these gauges. The sender can get less accurate after some time. Perhaps the needle moves only very little when the water T° rises from50 tot 80°C. In think the best option is replacing the sender unit and get the gauge overhauled or buy an exchange one. Quote Link to post Share on other sites
Guest ron Posted August 9, 2004 Report Share Posted August 9, 2004 Chris Try putting 12v across the terminals, it should go to full scale, as marvmul says they aren't very accurate in normal use but they should be consistent. Ron Quote Link to post Share on other sites
BryanD Posted August 9, 2004 Report Share Posted August 9, 2004 Can someone tell me what the resistance of a properly functioning Temp sender should be when 'cold'? My temp gauge rarely gets much off the end stop - although it gives a full deflection when the sensor cable is earthed. I don't believe the engine is running that cold, especially in this weather.... Quote Link to post Share on other sites
jean Posted August 9, 2004 Report Share Posted August 9, 2004 Chris, if your temp. and fuel meter are showing the same error the voltage stabilizer is faulty. The guages are calibrated to work with a voltage of 10 volts. For sure there will be full deflection on the guage at 12 or 14 volts. The stabilizer is in fact a bimetal strip switching the voltage to the guages from 0 to 12 volts in an on/off cycle. The guages will read the average voltage produced by the on/off ratio, to say 10 volts for a correctly operating stabilizer. On my 6 the needle only moves over half way in extreme conditions in general it stays in the middle, any further the fan will cut in. Jean Quote Link to post Share on other sites
Chris Tyrrell TR6 Posted August 9, 2004 Author Report Share Posted August 9, 2004 My fuel gauge is functioning correctly so that would indicate that the voltage stabaliser is okay. I'll put 12V across the gauge tonight and see if I get full needle movement. Many thanks. Quote Link to post Share on other sites
BryanD Posted August 9, 2004 Report Share Posted August 9, 2004 So disconnecting the the sensor end of the cable, then putting a voltmeter between it and earth should show a voltage of 10v ? Quote Link to post Share on other sites
john.r.davies Posted August 9, 2004 Report Share Posted August 9, 2004 All, esp. Bryan, I recently tested a new temperature sender, using a water bath gradually heated from room to boiling temperature. I measured the resistance with a multimeter and the actual temperature of the sender with a remote infrared thermometer. The resistance of the sender varied from 1 Ohm at 40 degrees C to 0.1 Ohm at 100 degrees C. There was a little 'sag' in the straight line between these two points. I couldn't heat the sender any more, to working temp. without seriously modifying a pressure cooker, and she wouldn't let me. An old sender had a smaller range, with a higher resistance when cold and almost the same when hot. Hope that helps! John Quote Link to post Share on other sites
Chris Tyrrell TR6 Posted August 9, 2004 Author Report Share Posted August 9, 2004 Well, I removed the gauge again and applied 12V across the terminals and the needle travelled the full range. I think I'll replace the sendor and see if that makes any difference. I sat in traffic with the sun beating down for an hour on my way to Malvern and the needle didn't go past half way. The car does generate a lot of heat but perhaps I'm not giving the old girl enough credit and expecting her to overheat! Quote Link to post Share on other sites
Guest ron Posted August 10, 2004 Report Share Posted August 10, 2004 Chris If it's any help mine normally sits between 1/3 and 1/2 scale and climbs slightly to just below 1/2 if ticking over for a while on a hot day [mechanical engine fan] what I would be looking for is any change to the norm rather than the actual reading. Ron Quote Link to post Share on other sites
Chris Tyrrell TR6 Posted August 10, 2004 Author Report Share Posted August 10, 2004 Well that interesting Ron. Mine gets up to just under half way within 10 minutes or so and then doesn't move at all, moving or static traffic. Mine also has the original mechanical fan. Perhaps I should leave things alone and just monitor the gauge for any change. One gets used to modern gauges where the needle reaches the top of the range and then drops back as the fan kick in, at least that's what happens to the unreliable modern car I own (Vectra...I'll never buy another Vauxhall), I'm even considering changing it for another classic. Just need to convince the wife! Quote Link to post Share on other sites
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