The 'E' Type Forum

I have started for the first time the motor some days ago but the water temp gauge does'nt work. How can I check it ? I have fitted a new thermostat, wiring beetween thermostat and gauge is OK .

Your voltage stabiliser may have failed, they do that a lot, I am on my SIXTH !

Is your fuel gauge working? if not then its almost certainly your stabiliser, check you are getting 10.5V out of it.

My fuel gauge is OK but what and where is the voltage stabiliser?

Behind your drop down dash panel, it has 2 connections each with TWO connectors, in your top left hand side of the flap. If your fuel gauge is working then you may have a bad connection to your water temp gauge from the VS.

Just earth the wire you have arrowed and see if the guage moves

I would be careful earthing the wire at the sender. If the gauge is working it will whiz straight off scale. If you have a 47 ohm resistor to hand short the sender wire to earth via the resistor...kinder to the gauge. They rarely fail so suspect the wiring of voltage regulator (or even the new sender) before the gauge.

Ian Is the voltage stabiliser the part where the wires 3 and 4 are connected ? What must I test on these wires? How the temp sender can be tested?

If you have access to an analogue meter...an Avo 8 is ideal then point 4 should be battery voltage...around 12 to 14 volts depending on whether the engine is running. Points 3 and 2 should show a regulated 10 volts irrespective of engine speed and point 1 will be less than 10...its voltage depends on the temp.
If you have a digital meter then point 4 will be 12 to 14. Points 2/3 may show random readings around 10 as the voltage regulator works like a flasher unit turning on and off to give an average 10 volts....analogue meters will show the average whereas most digital ones will not. They show the instantaneous voltage when sampled by the meter hence the digits will wander. An excellent example of where an analogue meter beats its modern digital successor and an Avometer is the rolls Royce of analogue meters.

If point 2/3 is 12 to 14 volts the reg is dead short circuit. If point 2/3 is zero volts the reg is dead open circuit.

The sensor itself is a thermistor with a negative temperature coefficient... It's resistance falls as it heats. I just measured mine cold with a fluke 289 digital meter and its resistance is 614 ohms. It will be a lot less at operating temp....around 100 too 200 I would guess. Hence unwise to ground the sensor lead as the meter will whizz instantly off scale.

Hope this helps? Incidentally if your regulator is dead it is a good idea to simply scrape out the mechanical innards and replace with a modern 10 volt low drop out linear voltage regulator. There is a thread on the forum on how to go about it i think? If not then try the internet or pay someone loads to supply a ready converted one. You can diy as the bits cost a couple of pounds at the most.

HI CACTUSMAN I have 12 v beetween 4/body and 1.5 v beetween 2 or 3 and the body . So if I have understood what you said I am beetween dead short circuit and dead open circuit ? anyway it seems that my voltage stabiliser is not right.

Moreover I just tested the resistance between the sensor and the motor and it is always 0 ohm. Is it normal? I did the same test with both the old sensor and the new one.

Hmmmm...Zero ohms is most definitely wrong. Did you disconnect the wire first? Make sure the lead is removed before you measure or you will be measuring the wiring and gauge etc and get a nonsense reading?
As I said the sensor is a thermistor.... A resistor whose resistance is temperature dependent. I measured mine yesterday and it was a bit over 600 ohms cold. Take it out and measure again between the connector and the thread. If it really is zero bin it.

As to the 1.5 volts that does not sound right either. Does the fuel gauge behave as it too is powered by the reg? Try disconnecting the wire from the reg at point 2/3 so the regulator is not loaded by the water or fuel gauges and re test to see if it is 10 volts. If you listen very carefully to the regulator it should be ticking much like and indicator flasher but much quieter.

If the sensor or the wire to the sensor has shorted out then the gauge may have tried to whiz beyond Max and been damaged. It may also have caused damage to the regulator...

Disconnect both wires from the gauge and measure the resistance. Not sure what it should be but it should not be zero and it should not be open circuit...infinite. I would guess somewhere around 10 to 100. I will check mine on Monday as I am away from the car till then.

Good luck!

Hi Julian.....by earthing the lead to the sensor the meter needle will not whiz off the scale, the meters have a bimetalic strip and a heating coil wire so when you touch the lead to earth the needle will rise up the scale......i wouldnt leave it connected permenantly but you will get instant results.....

Yes...a brief touch will move the needle. Still much wiser not to short but use a resistance...say 100 ohms. Meter will still move probably to Max but you limit the current through the rather delicate heating coil in my view.

Right.

Here are readings taken off my car.

Resistance of sensor cold is 630 ohms today - bit chillier!

I used a variable resistor in parallel with the sensor to mimick hot (saves starting and waiting for the car to warm). Gauge shows 70 dec C when the equiv sensor resistance is around 80 ohms. Measured with a fluke 289 digital meter.

Thus if you have a 100 ohm resistor across the sensor when cold the gauge should move to somewhere around the middle (70 dec C)

Measuring the voltage at the sensor (point 1 on your pic) using my trusty analogue Avo meter with the ign on.

Cold voltage is around 8.5 volts.
Hot the voltage is around 5 volts.

The Avometer needle dances around a bit as the reg flashes on and off.

I tried measuring the voltage with my Fluke digital meter and the reading was meaningless.

So your readings should be somewhere around these if the regulator/gauge/sensor are working correctly although I would allow a tolerance of =/- 10% at least.....we are not talking precision electronics!

Hope this helps. Julian

My two temp senders give me 0 ohm when they are cold and separated of the car ( the old on the photo as the new one!) If I have understood, I should have a minimum of about +-100 Ohms

May be are they both non functional ?

Hi Yves...you need to connect one lead of the meter to the thread part of the sender and the other lead to the connector on top of the sensor where the wire connects

Mgcjag beat me to it. One probe to thread and one to the screw term on the top where you connect the wire. Room temp look for around 600 ohms plus or minus 50 ohms depending on how hot your room is. Drop in a mug of boiling water for a minute, fish out while hot, dry with kitchen roll and immediately re test. You should see somewhere around 80 to 200 ohms I would guess depending on how hot. Don't burn your fingers!!!!

I will almost guarantee it does work...thermistors are pretty reliable. If it does indeed work th n suspect either the gauge or reg. The gauge, as described above, has a small heating coil that warms a bimetallic strip that bends and moves the needle. Measure the resistance of the meter between the spade terminals. I would imagine it will be somewhere around 10 to 50 ohms. If the weather is not too not to dismal I will measure mine. If your meter is open circuit....high resistance then the coil has failed. I would imagine someone somewhere could mend but may be simpler to get a replacement. They do turn up on a well known auction site quite frequently!!

It's the same result ...

Are you sure the meter is zeroed?. The needle is past 0. Somewhere there though be a zer o adjust. Short the probes and adjust till the meter is on zero ohms. Then measure. If it still gets to zero then, yes, dud thermo sensor....although it would mean your needle would have gone to Max and possibly burned out the sensitive heating coil sadly.

Incidentally if anyone wants the best analogue meter for classic car electrics look no further than the Avo mark 8.

Lots of info here

http://www.richardsradios.co.uk/avo8.html

Avoid the mark v and above as they have inferior quality switches and meter movement.

There are usually a few on eBay. These were among the best meters money could buy when new. No analogue meter for sale today comes anywhere close to an Avometer.

Thank's for theese exhaustives informations about ammeter.... I feel quite ridiculous with my coreen ammeter !