ChrisJ15
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| posted on 26/4/25 at 04:45 PM |
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Caerbont Temp Sender Test
Hi,
My J15 has had constant problems with the Caerbont temperature sender/gauge combination. It works for a while then decides to massively over read.
Has anyone got a range of resistance values I can use to check the (TT3001-8N) sender before I order another one please?
I did measure 54 Ohms at 80ish Deg C which is within the range for the sender (287-23 Ohms for 40 - 120 Deg C) but may not be correct.
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gremlin1234
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| posted on 26/4/25 at 05:03 PM |
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check the earth, (chassis ground) engine to body to battery neg
[Edited on 26/4/25 by gremlin1234]
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ChrisJ15
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| posted on 26/4/25 at 05:54 PM |
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Thats always been a challenge because its mounted into a plastic housing which means it has to bolt onto a connector.
This has worked OK in the past and its been taken off and cleaned up and shows good continuity to earth.
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ChrisJ15
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| posted on 27/4/25 at 06:34 AM |
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One thing I noticed which was strange was that I get a different temperature reading with the ignition switched on but engine not running to when the
engine is running (higher when running).
I had posted this same problem some years back and someone asked if I should be using a voltage stabiliser. I discounted this because there's
nothing in the Caerbont instructions for the gauges for this.
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gremlin1234
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| posted on 27/4/25 at 07:55 AM |
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quote:
I discounted this because there's nothing in the Caerbont instructions for the gauges for this.
this page shows some caebont gauges require a voltage stabilizer
https://www.smiths-instruments.co.uk/app/uploads/2024/08/PIL128-Bi-Metal-diagram.pdf
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Mr Whippy
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| posted on 27/4/25 at 01:23 PM |
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quote:
Originally posted by ChrisJ15
One thing I noticed which was strange was that I get a different temperature reading with the ignition switched on but engine not running to when the
engine is running (higher when running).
I had posted this same problem some years back and someone asked if I should be using a voltage stabiliser. I discounted this because there's
nothing in the Caerbont instructions for the gauges for this.
Those symptoms are very obviously voltage related
Fame is when your old car is plastered all over the internet
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ChrisJ15
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| posted on 28/4/25 at 06:51 PM |
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I don't think the gauge (Caerbont ICT1-1452-01B) requires a voltage stabiliser.
The instructions that came with them were clear and showed direct connection to 12V via a 3A fuse with no mention of voltage stabiliser.
I've ordered a 500 Ohm potentiometer so I can test the gauge with the engine on and off as a starting point for diagnostics.
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ChrisJ15
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| posted on 3/5/25 at 09:51 AM |
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To test whether it's the sender or the gauge I connected the 500 Ohm potentiometer in place of the sender and moved it through the range of my
sender (287-23 Ohms representing 40 - 120 Deg C):
Engine off I needed 6 Ohms to get 120 Degress on the gauge and Engine running I needed 40 Ohms. Neither are correct (should be 23 Ohms).
The thing that stands out is I adjusted the potentiometer to get the gauge saying 90 Degrees with the engine off and when I started it it jumped
straight up to 120 Degrees.
That to me suggests there's some internal voltage stabilisation in the gauge (Caerbont ICT1-1552-01B 52mm 12V Water temp) which isn't
working. The voltages involved were pretty normal (12.67V off 13.87V running). The other gauges are the same spec and none of them are different with
engine on/off.
So looks like I need another Caerbont temp gauge which is an absolute PITA because I have to remove the centre tub to get to the gauges and thats a
big job, just when I want to be using it! I wasn't impressed with Caerbont before I fitted the gauges so should have used a panel to be able to
remove them easily. Very frustrating!
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gremlin1234
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| posted on 3/5/25 at 11:23 AM |
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quote:
Originally posted by ChrisJ15
So looks like I need another Caerbont temp gauge which is an absolute PITA because I have to remove the centre tub to get to the gauges and thats a
big job, just when I want to be using it! I wasn't impressed with Caerbont before I fitted the gauges so should have used a panel to be able to
remove them easily. Very frustrating!
or leave the gauge in place, and fit an external voltage stabilizer.
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ChrisJ15
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| posted on 3/5/25 at 05:47 PM |
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I did think about adding a 12V to 12V Voltage regulator but they all show two wires in and two wires out. I could only intercept the positive going
from he fuse to the dash area and not sure if the two negatives could be common.
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gremlin1234
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| posted on 3/5/25 at 07:09 PM |
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quote:
Originally posted by ChrisJ15
I did think about adding a 12V to 12V Voltage regulator but they all show two wires in and two wires out. I could only intercept the positive going
from he fuse to the dash area and not sure if the two negatives could be common.
common chassis ground should not be a problem.
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gremlin1234
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| posted on 4/5/25 at 02:08 PM |
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quote:
Originally posted by gremlin1234
common chassis ground should not be a problem.
to add, in this case, common chassis ground is ideal, but if you have canbus or other sensitive
electronics, you should use an explicit 'ecu' ground.
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ChrisJ15
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| posted on 4/5/25 at 04:19 PM |
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Thanks for the replies, no Canbus.
I think my approach will be. Buy new Gauge/Sender as neither appear to be working correctly.
Buy 12V Voltage regulator and see if this works temporarily, then when convient to take tub off change whole thing but retain voltage regulator (have
had other intermittant problems with oil pressure gauge).
I did think perhaps the problem is having a small gel racing battery rather than a larger battery which would smooth out the voltage fluctuations
more.
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TimC
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| posted on 9/5/25 at 10:55 AM |
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In my experience, Caerbont/Speedy Cables are brilliant to deal with. Have you spoken to them?
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ChrisJ15
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 posted on 10/5/25 at 10:17 AM |
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Thanks but I already had a new gauge/sender and voltage regulator. I didnt think fixing would be wroth it when the gauge is ~£50 plus didnt want the
car unusable for a period of time.
All fitted and seems to be working OK.
Did a few other jobs which had been waiting for the central tub to be off and then noticed the clutch master has been leaking into its rubber boot.
Who said kit cars are never finished! That one can go into the list of 'things to do when front clam off'! 
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