ijonsson Posted September 30, 2017 Report Share Posted September 30, 2017 I'm confused, I have a "modern-classic" Smith electric temp. gauge and it shows over 100 deg C when I can measure around 75 deg C with an IR thermometer on various parts of cooling system including the sender and I'm sure the thermostat has opened. I have 9-10 V feed to the gauge. At ambient temperature the sender has about 1050 ohm resistance, I have two other senders, an old one with approx 500 ohm and another brand new one with approx 850 ohm. Which one should I use, by instinct I would say the one in the car as higher resistance should give lower reading, but ....? Quote Link to post Share on other sites
RogerH Posted September 30, 2017 Report Share Posted September 30, 2017 Hi Inge, they are not precision items. Why not try the others and see which gets closest. Roger Quote Link to post Share on other sites
barkerwilliams Posted September 30, 2017 Report Share Posted September 30, 2017 Inge, Remove sensor from car, fit a 5/8 UNF bolt into hole to stop water leaking. (or rolled up piece of card) Connect threaded part of sensor to an earthed part of engine with wire. Refit the loom sensor connection. Lower sensor into a mug and wedge mug suitably near engine. Boil kettle of water Fill mug with boiling water turn on ignition and read the temp gauge Alan Quote Link to post Share on other sites
ijonsson Posted September 30, 2017 Author Report Share Posted September 30, 2017 Inge, Remove sensor from car, fit a 5/8 UNF bolt into hole to stop water leaking. (or rolled up piece of card) Connect threaded part of sensor to an earthed part of engine with wire. Refit the loom sensor connection. Lower sensor into a mug and wedge mug suitably near engine. Boil kettle of water Fill mug with boiling water turn on ignition and read the temp gauge Alan OK, maybe it's time for a cuppa Quote Link to post Share on other sites
john.r.davies Posted September 30, 2017 Report Share Posted September 30, 2017 Plus 1, for Alan's procedure, but I'd boil the water on a camping stove, measuring the temperature of the water, and the gauge reading, as I go. Then you have a curve, that you can extrapolate beyond 100C as the pressure cap on theradiator will prevent the coolant boiling until about 120C. Temp senders are very "iffy" these days! John Quote Link to post Share on other sites
ijonsson Posted September 30, 2017 Author Report Share Posted September 30, 2017 Did test and the best one is actually the one that I had fitted in the car Quote Link to post Share on other sites
MikeF Posted October 1, 2017 Report Share Posted October 1, 2017 This may be a red herring. The original sensor on side screen cars is a capillary device. In later cars the sensor is electric and needs a stable voltage to work accurately [which is wired in], but is not present on earlier cars. An electrical sensor could well be affected by changes in charging/battery voltage etc unless a stabilizer is included in its workings. Readings certainly do change on later cars when the voltage stabilizer fails) Mike Quote Link to post Share on other sites
ijonsson Posted October 2, 2017 Author Report Share Posted October 2, 2017 This may be a red herring. The original sensor on side screen cars is a capillary device. In later cars the sensor is electric and needs a stable voltage to work accurately [which is wired in], but is not present on earlier cars. An electrical sensor could well be affected by changes in charging/battery voltage etc unless a stabilizer is included in its workings. Readings certainly do change on later cars when the voltage stabilizer fails) Mike I've measured the output from the stabilizer, it's 9-10V Quote Link to post Share on other sites
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