Gully Posted August 5, 2017 Report Share Posted August 5, 2017 Hi all, When heading across to the Silverstone Classic last weekend I looked down and was horrified to see the temperature guage reading just below the red (car usually runs mid point on the gauge). I pulled over and nothing appeared to be amiss - hoses all at usual temperatures - so I gave the thermostat housing a couple of sharp taps to ensure the thermostat wasn't sticking: no change in reading. I then drove a bit further, with the car seemingly running normally, before stopping to check under the bonnet again. After a quick wiggle of the sender connection the gauge dropped to zero, where despite further wiggling it stayed for the remainder of the journey to Silverstone. Later on in the afternoon before the parade lap I wiggled the connection again and the temperature gauge read perfectly normally for the parade lap and journey home... Sorted, or so I thought, but clearly a dodgy connection to keep an eye on. I took the car to an evening show on Tuesday and on the journey out the car read normal temperature, but on the way home higher than normal, so I decided to buy a new sender. Fitted that this morning (before the rain) and took the car for a run - the temperature started climbing more quickly than usual and within half a mile was off the top of the gauge! Under the bonnet all the temperatures seem completely normal. Rubbish parts? I did buy from an eBay seller, so have another sender on order from Canleys, but any thoughts as to what else could be wrong? Fuel gauge is working fine, so voltage stabiliser should be okay. I replaced the thermostat a few months ago and the engine temperatures seem to be fine and consistent - warms up, thermostat opens, radiator gets hot, all other hoses warm up - whatever the temperature gauge says! Thanks, Gully Link to comment Share on other sites More sharing options...
Pete Lewis Posted August 5, 2017 Report Share Posted August 5, 2017 sounds like youve been sold a 121997 sender for old moving iron gauges not the GTR108 you need for bimetal stabilised mix and match the two very different systems and you get high readings all the time ... seen one guy changed his engine on the old forum for this cock up pete Link to comment Share on other sites More sharing options...
Ben Caswell Posted August 5, 2017 Report Share Posted August 5, 2017 Could be the voltage stabilizer playing up watch the fuel gauge if that climbs up to full at the same time then thats your suspect. Link to comment Share on other sites More sharing options...
Gully Posted August 5, 2017 Author Report Share Posted August 5, 2017 Could be the voltage stabilizer playing up watch the fuel gauge if that climbs up to full at the same time then thats your suspect. Thanks Ben, but the fuel gauge is fine. Gully Link to comment Share on other sites More sharing options...
Gully Posted August 5, 2017 Author Report Share Posted August 5, 2017 sounds like youve been sold a 121997 sender for old moving iron gauges not the GTR108 you need for bimetal stabilised mix and match the two very different systems and you get high readings all the time ... seen one guy changed his engine on the old forum for this cock up pete I wondered - will report again once I have the new one from Canleys! Thanks, Gully Link to comment Share on other sites More sharing options...
DrKai Posted August 10, 2017 Report Share Posted August 10, 2017 (edited) my temp was reading constantly high but excluded stabilizer on basis that fuel gauge always seemed fine. after going through pretty much every other part of the heating system i thought XXXX it and replaced the stabiliser... et voila perfectly cool gt6 (the engine at least) Edited August 10, 2017 by KevinR Swearing XXXX'd out Link to comment Share on other sites More sharing options...
Pete Lewis Posted August 10, 2017 Report Share Posted August 10, 2017 Dr K im no moderator but i feel you should edit the F word , its bad practice , best use something more suitable 1 Link to comment Share on other sites More sharing options...
DrKai Posted August 10, 2017 Report Share Posted August 10, 2017 my bad folks wasnt thinking Link to comment Share on other sites More sharing options...
Gully Posted August 10, 2017 Author Report Share Posted August 10, 2017 Well, new sender arrived from Canleys earlier in the week and as tonight was the first dry evening since it landed I've now fitted it and test driven. Result - reads high off the scale in exactly the same way the previous replacement did! Grrr. Again, everything else seems normal. Once it's cooled down I may try re-fitting the original, as that was reading sensibly intermittently. I guess I now need to decide if I try changing the voltage stabiliser next, or replacing the thermostat again. Gut feeling is that the fault is electrical. Interestingly, even though I've changed the speedometer previously, I've never found the voltage stabiliser, so some tracing of cables is going to be needed! Gully Link to comment Share on other sites More sharing options...
Pete Lewis Posted August 10, 2017 Report Share Posted August 10, 2017 its supposed to be held on the back of the speedo case with a single screw if its dangling it will read full voltage as the stab. case must be earthed Pete Link to comment Share on other sites More sharing options...
Gully Posted August 10, 2017 Author Report Share Posted August 10, 2017 its supposed to be held on the back of the speedo case with a single screw if its dangling it will read full voltage as the stab. case must be earthed Pete No sign of anything voltage stabiliser-like dangling loose behind the dash. I did fleetingly look for one when I changed the speedo back in the Spring as I knew it should be there, but everything was working and I dismissed the fact I couldn't find it. I've ordered one just in case and will pull out the middle panel to trace the feed to the gauges (supposedly from the hazards switch via the stabiliser), but not tonight - the light is fading! Gully Link to comment Share on other sites More sharing options...
JohnD Posted August 10, 2017 Report Share Posted August 10, 2017 If you have one, the supply to the gauge (which then goes to the sensor) should read 12V - 0V - 12V - etc. if you have an OE one, or 10V if you have a modern one. And calibrate your sender and gauge. A pan of water on a camping stove,sensor in the water on extension leads (supply and earth). Heat the water, observing water temp And gauge reading, until it boils. Ow you know what the gauge means. John Link to comment Share on other sites More sharing options...
dougbgt6 Posted August 11, 2017 Report Share Posted August 11, 2017 As Ben and Dr K pointed out earlier on, the stabiliser supplies both the temperature gauge and the fuel gauge so both will be affected if it's a stabiliser problem. You may have a modern electronic one, these are quite light and can dangle anywhere behind the dash they have 3 wires, 12 volts in, 10 volts out and earth. Link to comment Share on other sites More sharing options...
Gully Posted August 11, 2017 Author Report Share Posted August 11, 2017 As Ben and Dr K pointed out earlier on, the stabiliser supplies both the temperature gauge and the fuel gauge so both will be affected if it's a stabiliser problem. You may have a modern electronic one, these are quite light and can dangle anywhere behind the dash they have 3 wires, 12 volts in, 10 volts out and earth. Yes, that's why I said In my initial post that I didn't think it was the stabiliser, but will have a good root around behind the dash over the next few days and trace where the supply to the gauges is coming from. According to the wiring diagram, there should be a feed from the hazard light switch to the stabiliser and from there in light green wires to the gauges. Will put the voltmeter on them in the first instance. Gully Link to comment Share on other sites More sharing options...
Gully Posted August 14, 2017 Author Report Share Posted August 14, 2017 Saying this quietly as I believe these cars listen, but I think it's fixed! I started off yesterday by trying John's suggestion of testing the gauge / sender combinations using nigh on boiling water and carefully immersing the sender. That showed that the old sender first removed as faulty read much lower than both the new ones (which were very similar). The new ones appear to be a single piece of machined brass, whereas the removed one is steel bodied with a copper sensor section inscribed Smiths Industries. On the basis that very hot water was giving me a reading below red, I began to wonder if the thermostat could be faulty... Having removed the thermostat, I checked it in a pan of steadily heated water alongside a spare I had in the shed. Both 82C stats and they opened together and fully, so I reinstalled and tested - same result: gauge rose rapidly and was off the top of the scale before the thermostat opened, but with no sign of overheating. Pushed the car back under the car port and left it to cool overnight. The only positive of removing and refitting the thermostat was that I removed a large piece of debris threatening to block the intake manifold pipe (looked like build-up from behind the sender). This morning I decided to check out the voltage stabiliser. I removed the dash centre panel and initially checked the voltage being fed to the temp gauge and fuel gauge - both read just over 12 volts. I then searched around a bit, but no stabiliser. I knew there wasn't one on the back of the speedo and I soon spotted a dark green feed connected to a pair of light green cables and by their location presumed that the voltage stabiliser had been deleted at some point in the car's history. I pulled the spades apart and re-checked the feed to the gauges which was gratifyingly non-existent! A new voltage stabiliser had arrived from Rimmers earlier in the week and I fitted it into the circuit, mounting it on the rear of the speedo to earth it. Hey presto - 10v at the gauges. Having run the car up to temperature (and covered a few miles in it tonight as a proper test), I can report the temperature gauge is now functioning normally with the new sender and stabilised voltage to the gauge. Happily, my over-reading fuel gauge is now accurate too (never dropped below a quarter before at lowest point and I'd previously bent the float arm so it was a quarter tank at this point, so returned the arm to the right profile this afternoon). So an interesting fault to chase through - I'd love to know what the specification of the sender was that went on the blink originally, as it had been working perfectly happily for at least 4 years giving sensible readings with a 12v feed to the temperature gauge! Many thanks to all for your helpful suggestions. Gully Link to comment Share on other sites More sharing options...
Pete Lewis Posted August 15, 2017 Report Share Posted August 15, 2017 Its probably a121997 for non stabilised moving iron gauges , thats a bit of a guess pete Link to comment Share on other sites More sharing options...
JohnD Posted August 15, 2017 Report Share Posted August 15, 2017 Thanks for the debrief, Gully! Its good to know that an ordered investigation, measuring the parameters, has identified the problem and found the solution. Much better, and cheaper, than semi-random replacement of parts. If I may, better than dunking the sensor in boiling water is to heat it from cold, noting the temp and gauge response. As you say, 100C is colder than the running temp of the coolant, and you can't easily heat the sensor more than that to test it. But "extrapolating" the curve of gauge response will show you what it will be in operating conditions. John 1 Link to comment Share on other sites More sharing options...
dougbgt6 Posted August 15, 2017 Report Share Posted August 15, 2017 But, there was a period of time, years, when the system appeared to be running fine without a voltage stabiliser? I had a klaxon on my car which stopped working, when I lifted the bonnet someone had hacksawed it off! Couldn't even be bothered to undo the bolts! Perhaps the same person did for your VS? Link to comment Share on other sites More sharing options...
Ben Caswell Posted August 15, 2017 Report Share Posted August 15, 2017 Good to get a final result well done. Link to comment Share on other sites More sharing options...
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