TR4 water temperature indication

[dave bailey]

I wonder if anyone can help with a problem concerning my water temperature indication. It's been a fault that I can't seem to get to the bottom of.

Switching the engine on (whether hot or cold) causes the water temperature gauge to slowly increase over a period of about 30 seconds to full scale deflection, where it stays till I turn the engine off. There is no problem with the engine actually overheating, so it's got to be an indicator problem. I've just fitted a new temperature transmitter --- same problem.   changed to a different gauge ---same problem. So all I'm left with is the Voltage Stabiliser, which I'm sure I changed not that long ago. 

Does anyone know how to check the voltage stabiliser?  I think I saw once that it produces 10V. (for some obscure reason). Although there are some things supplied via the voltage stabiliser, like windscreen wiper, flasher unit etc. they are just 'daisy chained' from it and work fine. The only other unit to be fed from the internal supply of the unit is the fuel, gauge  which is a bit odd in that a full tank shows as full for ages, but then moves down to empty relatively quickly. The tank then still having at least 20L in it. 

Any advice would be appreciated. 

Thanks. Dave.  

 

 

Edited August 27 by dave bailey

[john.r.davies]

Dave,

My first thought was the temperature sender, which is "Negative Temperature Coefficient (NTC) thermistor" whose resistance should fall as temperature rises.    While the OE ones work for many years, modern repros seem to fail quickly.   But you have excluded that - unless your new one was faulty?  Try another?   The gauges are just ammeters, very simple, unlikely to fail.

Which may leave the Volts regulator, but that supplies the fuel gauge too, so one would expect that to go awry as well.   It's there because the loom voltage in an OE dynamo-supplied car isn't stable - it's much better if an alternator is in place.   Anyway, the "regulator" works by NOT regulating the volts, but chopping them!     A multimeter set to volts if quick enough will show 12V (or whatever is the current state) - 0V - 12V - 0V - etc.   By chopping the voltage, it averages 10V as seen by the well damped gauges, and does so in the face of a varying supply.  Cunning, eh?

The OE 'regulator' is a simple switch controlled by a bimetallic strip.    On, the strip warms up, bends and opens the switch.  Off, it cools down untul the switch makes contact again.  And so on.  Simples!    Modern electronic regulators do supply a constant 10V, also easily found by a multimeter,, but some cheapoes are so slow they can't tell the difference.

See:  https://bullfire.net/TR6/TR6-44/TR6-44.html  

John

 

[dave bailey]

Hi John, thanks, I understand a bit more about the system now. Measuring the voltage out at the stabiliser to the gauges, it reads loom voltage ie 12.6V engine off, 13.6V engine running. (the gauge is still going to FSD. hot.) I have quite a good mutimeter, and assume that the voltage should show 10V. So I guess that the stabiliser is U/S.

Dave.

[RogerH]

Hi David

do not expect to see a stable 10V. It probably will not go over the 10V but what you read below is a mystery.

It may work perfectly - but...............

[RobH]

57 minutes ago, dave bailey said:

Hi John, thanks, I understand a bit more about the system now. Measuring the voltage out at the stabiliser to the gauges, it reads loom voltage ie 12.6V engine off, 13.6V engine running. (the gauge is still going to FSD. hot.) I have quite a good mutimeter, and assume that the voltage should show 10V. So I guess that the stabiliser is U/S.

The stabiliser doesn't sound to be working which is probably why the fuel gauge is reading oddly but that would just make the temperature gauge read a bit high, not go to 'hot' when the engine is stone cold. 

The fault you describe sounds as though you have a short circuit to earth somewhere on the sensor wire between the sender and the temperature gauge.  

A simple test would be to disconnect the wire from the sender. If the gauge returns to zero the wire is OK and the fault is in the sender.  If the fault persists with the wire disconnected, the wire is shorted to earth somewhere along its length.  

[dave bailey]

Hi Rob. I had exactly the same thought about 30 minutes ago. (after a couple of glasses or wine), So I'm going to string a wire directly from the sender to the gauge and see what happens. Interestingly the sender is earthed, but with this new sender it's a parallel thread, sealed with a fibre washer, I've also wrapped the thread with plumbers tape so I'm thinking that won't produce a very good earth. I will have to solder on a separate earth wire.  

 

[dave bailey]

1 hour ago, RogerH said:

Hi David

do not expect to see a stable 10V. It probably will not go over the 10V but what you read below is a mystery.

It may work perfectly - but...............

Thanks Roger, don't you find that life's a mystery?

[trchris]

Hi Dave 

l switched to an electronic stabiliser supposedly keeps a constant 10v been no bother…….yet 

Chris

[dave bailey]

Where did you get that from Chris?

[PaulAnderson]

I also have an electronic version of the voltage regulator, fitted maybe 15 years ago but can't recall at the moment where I got it from, perhaps eBay   I'll update if I do.

If you do a forum search on the term 'voltage regulator' everywhere you'll see over 450 posts mentioning it, and the answer might be in one of those. An example resultant thread is

Voltage Regulator RB106 problem - Technical - all models - TR Forums

 

[RobH]

Paul there is a confusion here. That link is about the dynamo control box.   The search needs to be for the  'instrument voltage stabiliser'  

This is the electronic version - you can tell because they list separate pos and neg earth versions. The original type work on either polarity. All the usual sources sell them e.g. :

https://www.autoelectricsupplies.co.uk/p/dashboard-voltage-stabilizer

 

 

Edited August 28 by RobH

[RogerH]

11 hours ago, dave bailey said:

Where did you get that from Chris?

Hi Dave 

for good or bad I bought mine from Moss 10+ years ago and still working fine.  There are many rantings saying how bad the Moss unit is but mine is good.  They are polarity sensitive. mine is NEG earth.

Roger

[roy53]

Watching this topic with interest Dave as my temp gauge reads very high .

After many tries to adjust I had a new transmitter delivered today but looks the same as already fitted with a white top.

water 70 but gauge reads just touching the red

Roy

[RobH]

Supposing your voltage stabiliser is working properly Roy, this can only be a mismatch of the sender and the gauge - it's a bit if a lottery whether you will find a temperature sender to match.   It's not easy,  but the best way may be to calibrate the gauge to suit the one you have.    - is that the adjustment you say you have already tried? 

https://centralcoastbritishcarclub.com/wp-content/uploads/2023/05/Fuel-Temp-Gauge-Calibration.pdf

The information I have says the TR4 used the GTR104 sender which is the red one:

https://www.minispares.com/gtr104-temperature-sender-transmitter-s-and-deluxe-mini-1964-1969

Edited August 28 by RobH

[Graham-P]

I had this, my temp sender connection snapped so purchased a new one from Moss which had a red ring beneath the connector and the gauge shot up to the red after a couple of mins running! I then learned that these are TR7 senders and the one I needed had a black ring. I managed to find  NOS on eBay from ANG Classis Car Parts, and now back to normal (pun intended). 
 

[stuart]

1 hour ago, Graham-P said:

I had this, my temp sender connection snapped so purchased a new one from Moss which had a red ring beneath the connector and the gauge shot up to the red after a couple of mins running! I then learned that these are TR7 senders and the one I needed had a black ring. I managed to find  NOS on eBay from ANG Classis Car Parts, and now back to normal (pun intended). 
 

Correct Graham. Ive posted about this several times, even my local autofactor states in their listings the red top is for TR7, all others need a black ring one.

Stuart.

[stuart]

15 hours ago, RobH said:

The information I have says the TR4 used the GTR104 sender which is the red one:

https://www.minispares.com/gtr104-temperature-sender-transmitter-s-and-deluxe-mini-1964-1969

Thats wrong Rob thats a TR7 one, its the black ringed one that is needed for earlier cars.

Interestingly though Robsport list the black ring version as Stag/TR7 though.

Stuart.

[RobH]

13 hours ago, stuart said:

Thats wrong Rob thats a TR7 one, its the black ringed one that is needed for earlier cars

If you look at that link Stuart, you can see they are selling a red one as GTR104 as do many other outlets. The GTR101 can come in black so perhaps that is the one better suited to early cars. 

The TR5 to TR7 is supposed to have the same GTR108 which is often shown with a black ring:  https://www.angclassiccarparts.co.uk/products/triumph-5981/tr7-tr8/heating-cooling/temperature-sender-switch-tr7-tr8-

the one with the red ring is normally a GTR104 used on lots of BMC cars with A and B  series engines.

These colours are a source of confusion as I don't even think they are a standard nor consistently applied.   The black ring was used both for the GTR108 sender and for the GTR102 - which was used on early BMC Minis which do not have a voltage stabiliser - and also the GTR101 which is very similar to the GTR104 above 70ºC.    

I think the GTR numbers are Unipart ones - Smiths used TT prefixes (e.g. TT3802/00  which is equivalent to GTR104)  

A lot of suppliers now seem to sell the TT6800/01 which is  a 'universal' sender with roughly the same resistance curve as the GTR 101/104 but it has the wrong thread and would need an adaptor. 

There will be a considerable variation between senders on the same gauge.  These are not precision devices and the specification on resistance is quite wide.  e.g. at 100ºC the GTR 104 can be anywhere between 42 and 57 Ohms. 

 

 

Edited August 29 by RobH

[trchris]

Dave l got mine from trgb

Chris

[stuart]

47 minutes ago, RobH said:

If you look at that link Stuart, you can see they are selling a red one as GTR104 as do many other outlets. The GTR101 can come in black so perhaps that is the one better suited to early cars. 

The TR5 to TR7 is supposed to have the same GTR108 which is often shown with a black ring:  https://www.angclassiccarparts.co.uk/products/triumph-5981/tr7-tr8/heating-cooling/temperature-sender-switch-tr7-tr8-

the one with the red ring is normally a GTR104 used on lots of BMC cars with A and B  series engines.

These colours are a source of confusion as I don't even think they are a standard nor consistently applied.   The black ring was used both for the GTR108 sender and for the GTR102 - which was used on early BMC Minis which do not have a voltage stabiliser - and also the GTR101 which is very similar to the GTR104 above 70ºC.    

I think the GTR numbers are Unipart ones - Smiths used TT prefixes (e.g. TT3802/00  which is equivalent to GTR104)  

A lot of suppliers now seem to sell the TT6800/01 which is  a 'universal' sender with roughly the same resistance curve as the GTR 101/104 but I think that is wrong for the TR5-6 and will probably make the gauge read high. 

There will be a considerable variation between senders on the same gauge.  These are not precision devices and the specification on resistance is quite wide.  e.g. at 100ºC the GTR 104 can be anywhere between 42 and 57 Ohms. 

 

 

ANG also sell the black ring one as being suitable for the saloons as well. https://www.angclassiccarparts.co.uk/products/triumph-5981/triumph-2000250025pi/heating-cooling/temperature-sender-switch-2000-2500-25pi

Last time we were here before is this thread. https://www.trforums.com/index.php?/topic/90926-tr56-faulty-temperature-sendergauge/

Intermotor 5273 worked for me the last time I needed one I think.

Stuart.

Edited August 29 by stuart

[RobH]

I've just found these resistance curves for the GTR101 and GTR104 senders. I now think these (or the equivalents) are the ones commonly sold as 'black' and 'red' respectively.

You can see that there is a lot of difference at first but that it narrows down above 60 degrees.  If you have a gauge  which is calibrated for the 'black' sensor but fit a 'red' sender instead, the engine will seem to warm up very quickly and at normal running temperature the gauge reading will be about 10 degrees high.  

I have shown that by the dotted lines.  The temperatures at which the senders reach (say) 100 Ohms are about 10 degrees apart. 

The same thing happens in reverse. If the gauge is calibrated for the 'red' sender then using the 'black' one will result in a slow rise from cold and a running reading about 10 degrees low. 

 

 

[john.r.davies]

It's not difficult calibrate your own sensor, by setting up a camp stove next to the car!

A pan of cold water over the stove, with the sender suspended in it, extension leads to the back of the dash board and heat it from cold, recording the water temp every few degrees with a cook's thermometer or an Infra red 'gun', and you can know exactly what the scale is on your gauge.

It will also show if the sensor is U/s!  As shown below.

John

Edited August 29 by john.r.davies

[dave bailey]

I guess you would also have to run an earth from the body of the sender to say, battery earth to complete the circuit?

[dave bailey]

I'm sorry I seem to have stirred up another debate on this subject. But for closure (I hope), I think that my problem is solved, having now replaced the voltage stabilser with one from TR Bitz and a sender from Revington TRs.

I say solved although the temperature seems to settle on the high side, around 210 deg. F. after 10 minutes running in the garage (not yet taken it for a run). I get the impression that this system is not particularly accurate, and depends on the matching of the individual components. I think that as long as you work out what your 'normal' is then it's still useable to show if something is not right. 

Thanks all for your inputs.

Dave.  

[john.r.davies]

"Extension leads"

So calibrate your new installation!   Know what "210F" really is!

John