Temp gauge Series 1 3500 oddness...

S

smudger

Member
The temp gauge on my S1 V8 started reading much lower than normal recently and then on Friday didn't work at all.
Wiring tested as usual - earth the sender terminal with ign on - gauge went straight up to red - no problem with wiring or gauge then - fit new sender, job done...

Except new sender doesn't register anything on gauge either...

I checked voltage in series between sender spade terminal and its Lucar terminal - 12v with ignition switched on but pretty wild all over the place with engine running. Is that even a useful test? No idea. There are no other electrical faults on the car that I know of.

The fuel gauge is steady and accurate so in theory no problem with voltage stabiliser?

So have I been really unlucky and got a duff brand new sender aswell (local independent parts shop, NOS aftermarket Raven brand made in UK)?

Or is something very peculiar going on...?

Any ideas or previous similar experience gratefully received...
 
Do a continuity check on the wire from the gauge to the sender terminal and try moving the wire about to see if it changes. It may be broken inside the insulation and the running engine vibrations are making and breaking.

Colin
 
Hi Colin. Thanks for that suggestion - I'll try that. I guess complete substitution of the wire from the sender to the gauge with a temporary length of wire known to be sound would also test the theory that the original wire although appearing to work ok with the earthing test, might be unreliable under actual running and road conditions? Simon
 
....To check the sender you can use a multi-meter to measure the resistance, This can be done by putting one probe on the brass nut of the sender and the other on the spade conector where the wire goes, there should be a reading, if it is goosed then there is no change. you could also use a test light and a battery as above. if the sender is goosed then the bulb wont light up. Can be done with out removing the sender....

The above is copied and pasted from this forum in 2003 with regard to another similar problem...

On trying the above test - the sender I have removed from the car shows no reading when tested as above.
The sender I have fitted to the car also shows no reading when tested the same way.
Both tests relying on the continuity meter power supply - no ignition switched on on the car...

So, does that show both the removed sender and the brand new one are both faulty if I've done it the right way?
 
Well, if it helps anyone else with a similar problem who has chanced upon this thread...

...yes, the continuity test was correct advice and proved to be conclusive - both the old sender on the car and the brand new one out of the box were duff. Another brand new sender was continuity tested straight out of the box and gave a resistance reading so was fitted to the car and works fine.
 
Poor quality parts are worst! Seems to be everywhere. Even our modern car, a 2008 Saab 9-3 fuel pump failed after less than a year. $400 plus a day of my time dropping the fuel tank wasted.
 
Good, glad you're sorted and it's also good to get the feedback. Very often questions get asked and suggestions made, then radio silence, leaving us non the wiser. I've learnt long ago that just because something is new, doesn't mean it can't be faulty. Which is why I've learnt to check all sorts of things to prove where a fault is.

Colin
 
Cheers Colin - I agree it can be frustrating to find an old thread that actually is really useful up to a point but then doesn't give the final answer. The one I found from 2003 was genuinely useful regarding the continuity test on the sender itself. I'm not an auto-electrician and that was new to me - but once learnt never forgotten.
But yep, sadly, don't trust new parts out of the box until you know they definitely work...
 
It is not rocket science. The temperature gauge is a resistor where the resistance varies with temperature. The resistance can be measured with any basic multi-meter.. If there is no resistance, i.e. an open circuit, the gauge is broken, (scraap0 Maybe a responsible supplier would test this before selling?
Perhaps someone with a good working temp. sensor could measure the resistance for a reference and post here
 
For what its worth, most of these sensors use NCT resistors, that is, Negative Coefficient of resistance, meaning the resistance goes down as temp rises.
 
jp928 said:
For what its worth, most of these sensors use NCT resistors, that is, Negative Coefficient of resistance, meaning the resistance goes down as temp rises.
Click to expand...
This would be useful to know. We replaced a 2000 TC sender with a new one, which has widely different characteristics to the original. It remains cold before shooting to max temp (moves from zero to hero in around 3 seconds), and remains until the engine cools again.

Have we been sold a pup, a engine temperature sender with a NCT resistance curve that suits a different P6 engine?? Or is the new part just bu99rd?
 
That doesnt sound like a curve, more like its shorting. To convince the supplier its duff I suggest you remove it, put it in very small pot and heat it, with a thermometer and meter attached and plot its resistance vs temp. Will see if I can find my old sender and test it.The temp sender is same for both S1 and S2 (568055), but different from the 4 cyls.
Am I right thinking your first post says the voltage on the sensor line is not stable? You should not see 12V there because the stabilizer should give a steady 10V.
Read this piece, noting that some of it refers to EFI systems that use 5V as base, rather than 10V I think our voltage stabilizer provides. There is a bit about testing a sender.

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I must say I have had no luck getting a reading on my old sender - which was NOT changed for a fault. on the 2k Ohm range meter would count up and then go 0L, for bigger than 2k. Next highesst ranges - 0L. ???
Next day - tested sender in car - 15C this morn, 1550 Ohms. Not convenient to run it today. Will report reading when hot.
 
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