RobH Posted July 16, 2020 Report Share Posted July 16, 2020 25 minutes ago, Mike 5 fan said: As a footnote, I recently had a faulty sensor, the first replacement had a red collar and was faulty, the second has a black collar and by new normal running temperature is now nearly ¾ up not ½ way as before. It's a little disconcerting. All sensors are not the same - there are differing resistance values and it sounds as though you have been supplied with the wrong type. This old thread might be relevant: Quote Link to post Share on other sites
Yarm 783 Posted July 17, 2020 Author Report Share Posted July 17, 2020 Hi Mike, that sort of doesn’t feel right, hopefully some advice will ensue from the Gathered royalty on this forum. I don’t even like the guage slightly over 1/2, let alone 3/4. Quote Link to post Share on other sites
AarhusTr6 Posted July 17, 2020 Report Share Posted July 17, 2020 Hi Good point on the sensor - I bought one of those heat guns, you know the ones for testing your bacon on the pan type things with a laser. Well temp guage was way over and heat pistol said 70 degrees so clearly not boiling so swapped hit sensor and this fixed issue. Quote Link to post Share on other sites
Mike C Posted July 18, 2020 Report Share Posted July 18, 2020 4 hours ago, AarhusTr6 said: Hi Good point on the sensor - I bought one of those heat guns, you know the ones for testing your bacon on the pan type things with a laser. Well temp guage was way over and heat pistol said 70 degrees so clearly not boiling so swapped hit sensor and this fixed issue. I also use infra red thermometers for a lot of cooling diagnostic work - engines and AC systems. They work well as you can quickly move from one component to another. I note the CV 19 checkers in the airports and shops are also using them. Quote Link to post Share on other sites
Waldi Posted July 18, 2020 Report Share Posted July 18, 2020 As long as you are aware of the limitations a relatively cheap IR (laser) temperature gun Is a good aid. Be aware of errors if you measure errors on metals (surfaces) like SS, copper, and aluminium (with includes aluminium containing high temperature paint). The emissivity of those materials is much lower, resulting in large errors. On cheap guns this cannot be corrected. Also the beam widens with distance, and what you see as a reading is the avg temperature in that beam. Thick materials like an engine block have a thermal gradient across the thickness, so you will measure a lower temperature than the actual inside temperature. If you are aware of these aspects, it can be a great tool. Examples: The inlet neck and bottom header of the radiator are very reliable areas where you can measure. The shiny SS returnpipe or the thermostat housing are less suitable. Waldi Quote Link to post Share on other sites
Z320 Posted July 18, 2020 Report Share Posted July 18, 2020 +1 for Waldi, he is absolutely right, Please let me add: ee see light/dark and color, this l laser guns sees hot/cold and emission. On cheap laser guns the emission rate is fixed by 90% (with dull wall paper) but metals are VERY different. Best is you know the temperature of the surface, modify the emission rate an your gun and then you can compare different temperatures of only this metal surface. See this photo. Why can you read Alfa Remeo? Why is the oil filler cap freezing? Quote Link to post Share on other sites
RobH Posted July 18, 2020 Report Share Posted July 18, 2020 This site has a good table of emissivities for various common materials: https://www.thermoworks.com/emissivity-table Note the vast difference in the first two listed - any polished metal is a very poor emitter but rusty or painted metals should read OK. Quote Link to post Share on other sites
AarhusTr6 Posted July 18, 2020 Report Share Posted July 18, 2020 Hi Yes . . interesting reading, mine was a cheap n cheerful but for the purpose of testing the guage saying it was boiling over it gave a good reading on the hoses and radiator and the swapping of the sensor worked. Rich Quote Link to post Share on other sites
Andy Moltu Posted July 18, 2020 Report Share Posted July 18, 2020 The issue with the sender being at fault is that it seems to read ok when the car is moving? Does the gauge move when you blip the throttle? If it does it might be an electrical gremlin causing the gauge to misread at low voltage. If the car only seems to overheat whist stationary it points towards an airflow issue. The fan switch not kicking in early enough may explain the car getting to a certain temp and holding at the level it switches on. If it continues to rise after the fan kicks in the question then arises as to whether the fan is shifting enough air. (Assuming it is shifting the air in the right direction. If you look at a modern car their fans seem to shift a fair bit more air than the after market ones sold for classics. Either they are genuinely more powerful or just damn noisy? I suspect aftermarket sales have to consider current draw to avoid flattening the battery of a classic with a dynamo or low output alternators. Quote Link to post Share on other sites
RobH Posted July 18, 2020 Report Share Posted July 18, 2020 (edited) There is a confusion creeping in here Andy. I think the diversion to sensors was in answer to the post from "Mike 5 fan", not to the original topic which as you say is nothing to do with sensors and seems to have been resolved by the OP. I think the reason modern cars have such powerful and noisy fans is that the radiators are proportionally smaller than those in old cars so need more help as it were. Edited July 18, 2020 by RobH Quote Link to post Share on other sites
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