makingff Posted November 27, 2014 Share Posted November 27, 2014 The water temperature gauge on my CSR is inaccurate at best and tends to spend most of it's time bouncing from zero to over 100 before eventually stopping at zero. I've replaced the temperature sender (twice), had the earth connector replaced (the one to the water rail) and so my attentions have now turned to the gauge itself.Not wanting to spend the £80 for a new one without being sure what the problem is, I got to thinking whether it would be possible to wire the gauge to the battery via a potentiometer so that I could test the gauge through a range of voltages and see if it behaves as expected (i.e. steady) or whether I get the behaviour I'm seeing when it's in the car.Is this a silly idea? If not, what sort of potentiometer should I be looking for? Is there another, easier way of testing the gauge? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 27, 2014 Member Share Posted November 27, 2014 Not silly: that's the way to do it. Do you know the resistance range for your sender, or is there anything written on the gauge?Jonathan Link to comment Share on other sites More sharing options...
makingff Posted November 27, 2014 Author Share Posted November 27, 2014 Hi Jonathan, thanks for the reply.I'll need to check on both (and nowhere near the car at present) but the sender is one from an aviation company that Aeroscreens posted on the old forum (I'll do a search in a bit) which goes to 120c (the Caterham one goes to 150c). The gauge is the standard Caterham one (so I assume it's the same as all the others). Is there some kind of formula I can use? Link to comment Share on other sites More sharing options...
makingff Posted November 27, 2014 Author Share Posted November 27, 2014 The sender I have is a VDO 323-095 which has a range of 10 - 180 ohm's and upto 120c. Not sure about the gauge's range though... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 27, 2014 Member Share Posted November 27, 2014 That's all you need to know. The potentiometer (or whatever*) needs to offer the same resistance. If you do the test with the gauge still in the car and using the car's battery don't forget to use a fused feed.Jonathan* For your purposes you could do this with a few fixed resistors. Link to comment Share on other sites More sharing options...
Bob L Posted November 28, 2014 Share Posted November 28, 2014 Garden of England - so Kent. Anywhere near Bexleyheath? I'd be happy to take my gauge off and let you borrow it for 10 minutes to prove if your sender / wiring is OK. I assume they are basically the same but mines a 1.8K of 99 vintage (if that makes much difference). Link to comment Share on other sites More sharing options...
makingff Posted November 28, 2014 Author Share Posted November 28, 2014 Hi Bob, I'm near Tunbridge Wells so not too far away but not that close. Thanks for the offer. I'll try the potentiometer route first as I think this could be quite a cheap and quick test but may take you up on the offer if it proves inconclusive.BTW, my last 7 was a 99 vintage 1.8k - it was a great car! Link to comment Share on other sites More sharing options...
Nigel Fox Posted November 28, 2014 Share Posted November 28, 2014 Dashboard gauges are usually a hot wire instrument. The current passing through heats a bimetallic strip or coil linked to the pointer. They are slow acting so shouldn't bounce around.Normally if you connect the temperature sensor terminal of the gauge to earth, the instrument should go to full scale. Link to comment Share on other sites More sharing options...
makingff Posted November 28, 2014 Author Share Posted November 28, 2014 Nigel, I thought of the test you suggest but want to be able to try the gauge at different settings for long periods of time, hence the potentiometer. If the gauge turns out to be fine then it must be electrical and my suspicion would be the earth as my speedo used to do the same thing prior to a well documented mod. Link to comment Share on other sites More sharing options...
LazerBrain Posted December 2, 2014 Share Posted December 2, 2014 I helped a ReHaBer do this with an old VW camper fuel gauge which did the same thing. He used the potentiometer to show the gauge moved through its full range, then was planning to leave it on a particular setting for a while to test what happened. Link to comment Share on other sites More sharing options...
makingff Posted December 22, 2014 Author Share Posted December 22, 2014 Bit of an update.Had planned to do a test using the potentiometer on Saturday but, as the weather was so good, decided to have a run out instead!Temperature gauge starter off quite erratic then settled down a bit although the needle would fluctuate with revs (more revs = higher temperature shown).What then happened was very odd. The oil pressure gauge needle moved to the far right and stayed there. The oli temperature was normal, then engine felt and sounded fine and even after stopping and restarting, the needle would just move to the far right and stay there. I'm assuming here that there isn't an oil pressure problem.This has got to be earth related so I'm going to look to replace the main earth cables and take it from there. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted December 22, 2014 Member Share Posted December 22, 2014 I'd be having similar thoughts. You can use temporary earth jumps to see if they fix it before you do it definitively.Jonathan Link to comment Share on other sites More sharing options...
makingff Posted June 14, 2015 Author Share Posted June 14, 2015 Solved at last! In case anyone is interested...Oil pressure gauge was the gauge and a new one fixed the problem.Water temperature gauge took a bit more work however I'm now an expert at removing the scuttle and also at soldering. It turns out it was the sender cable that was at fault. I removed and cleaned every earth connection I could find on the car - that didn't work. Eventually I created a new set of cables for each of the connectors on the gauge and, by a process of elimination, worked out which was failing. I ran a new cable via the heater from the sensor to the gauge and it's working perfectly!If only I'd tried this first... Simon Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 15, 2015 Member Share Posted June 15, 2015 Well done. Jonathan Link to comment Share on other sites More sharing options...
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