Temperature gauge reading high.

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Wellcroft

Member
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16
A bit of a strange one....

Temperature gauge on series 3 reading high.

Check all the obvious eg.

Sensor replaced with correct series 3 replacement
Voltage stabiliser replaced with electronic version. Out put from unit is 10.15V under tick over and rev'ing conditions Checked using both analogue and digital meters.
Earths checked and all good.

The odd thing is that the gauge is reading between cold and normal when the engine is cold. Check temperature when gauge enters the red and the temperature is 48 at the bottom and 68 (using infra red temperature unit) at the top on the radiator.

So fairly sure is the gauge. Can these be adjusted. Simpler option is to fit a durite or TIM gauge but it would be nice to get the gauge working.

ideas please
 
Have you checked the thermostat in boiling water and cold to see if correctly open and closed.
 
The voltage regulator should output just 10v , if you getting 10.5v that could make it read high
 

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Just check the temperature gauge now with ignition on, temp gauge showing between C and N and its 7 hours since running engine. Had same problem on old engine but since checking with hand held IT unit, knew the problem is common to both engines. CHECK ALL WIRING AND EARTHS AGAIN AND ALL IS GOOD. Will just put up with it until new Durite 2" mechanical unit arrives.

thanks for comments
 
Wellcroft said:
Just check the temperature gauge now with ignition on, temp gauge showing between C and N and its 7 hours since running engine. Had same problem on old engine but since checking with hand held IT unit, knew the problem is common to both engines. CHECK ALL WIRING AND EARTHS AGAIN AND ALL IS GOOD. Will just put up with it until new Durite 2" mechanical unit arrives.

thanks for comments
Click to expand...
Mechanical gauges are excellent things, used to have one in the 2a. You can see exactly what the temperature is.
 
Hi All.

Just gets more confusing.

Checked wiring again. Disconnected feed from voltage stabiliser to both temperature sensor and fuel tank level, 10.14 volts recorded at both terminal ends.

First . Reconnected temperature sensor, gauge was reading bang on N. Check voltage on sensor terminal (feed by green blue) wire) and reads 5.33 Volts which appears correct (50% = 5 Volts (half scale)).

Disconnected temperature sensor, and reconnected fuel level unit. Fuel reading was half full and voltage at the tank level unit terminal (feed by green brown wire) reads 4.98Volts. Again appears correct (50% = 5V)

Connected both temperature and fuel level, both readings readings exactly the same as before. so its appears that both displays are reading correctly.

Disconnected wire to temperature sensor and shorted to earth on the engine block and needle shot off the scale past red and half way across the H.

So it is possible that the sensor in not in the corrected position relative to the thermostat.

The engine is now a 2.5 tdi and using the original tapping point on the disco engine. The sensor is correct for a series 3 and not disco. I have used the series thermostat house with the side access point to the heater blanked off and the thermostat is between the disco and series parts.

Is it possible that as the engine does run a bit cooler and that the thermostat is not opening up so it is effectively is in a hot spot The thermostat was check prior to fitting to ensure it opens and closes (boiling water in a pan arrangement so should be ok).

Temperature at the bottom of the radiator is about 50 degrees and 68 degree at the top but the gauge is showing in the red.

Further thoughts please. Current trains of thought:-

moving the sensor to the heater feed hose when the new 'durite' unit arrives

removing the thermostat ( as the engine does run colder than the old series lump

many thanks for all your replies to date
 
200/300 tdi units do run cooler than the series. Why would you remove thermostat It's job is to have the engine and cab heater warm up as quickly as possible. Without out it you would have to drive for many miles in the winter to get any heat in the cab and for engine to reach it's proper operating temperature.
Forty year plus old gauge, old wiring, I would fit an aftermarket gauge that reads in numbers degrees and know what the engine is running at.
 
Hi All.

'Durite' temperature gauge arrived this morning and now fitted and surprise , surprise, the temperature is running at a steady 70. Took it up some serious hills, and temperature reached a maximum of just over 85 degree
Thanks for all your comments and particularly steve2286w who sent over the Gentlemans -guide- to- smiths-gauges.

I am now 99% sure as the the problem was the gauge especially since the gauge went to the nearly normal mark within a minute of switching on the engine.

For your information, I did the following checks which may be of help to others.

1) the voltage stabiliser is an electronic one and was giving out a constant 10.15V on tick over and under load
2) the earth was checked on the stabiliser and a separate earth added to ensure a good ground.
3) New series 3 temperature sensor was fitted.
4) No PTFE was used on the sensor thread and adapter. Sensor body was checked using a meter first from the brass body to a engine earth. Zero resistance.
5) Voltage checked to the sensor was 10.15V as per output from stabiliser
6) Disconnected wire to temperature sensor and shorted to earth on the engine block and needle shot off the scale past red and half way across the H.
7) Thermostat checked. Opening and closing correctly
8) Checked all readings with fuel level sensor disconnected. All were as expected

So I can only think it was the gauge.

Will let you all know if the problem comes back
 
Like I said old stuff, while mechanical items in good order, even of some age will be fine old electrics do deteriorate. The temp gauge in my series 3 is the other way when needle moves off the bottom it is up to running temp.
 
Hi Steve.

Yes. the 3 holes in the lower dash are now full.

One with the new temperature gauge, one with a volt meter Battery condition, and a twin USB outlet (for the phone and more importantly vehicle speed via a speed /GPS unit - my speedo is miles out with larger defender wolf wheels). Had the speed / GPS unit calibration checked by a friendly copper!

Derek
 
tottot said:
Like I said old stuff, while mechanical items in good order, even of some age will be fine old electrics do deteriorate. The temp gauge in my series 3 is the other way when needle moves off the bottom it is up to running temp.
Click to expand...
Interesting comment as the wiring is all new with 14 fuses fitted. A lot better than the original looms the previous owner had a big burn out and substituted some 20 + wires with 2.5mm house wires ALL IN YELLOW WITH SKOTCH LOCKS!!
 
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