Defender temperature gauge problems :(

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M

marwell

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46
Location
Gozo,Malta
hi lately i made a full restoration to my defender 90 and i have a problem with the temperature gauge..as i start the engine it works fine from cold but after a couple of meters it runs up to the red zone ...i removed the thermostat to see if it is jammed and left it out to see if it was the case and changes the sensor/sender twice, but it still runs up after some meters ...i checked the temp by hand and engine blocks and pipe are cool not hot... anyone got an idea :confused:
 
Temperature gauge on the landy works very simply, a regulated 10v positive to the gauge and then the other connection goes to the sensor which is earth (variable resistance, depending on how hot it is) Unscrew the instrument binnacle and check the voltage also run a bypass wire direct from the gauge to sender to rule out wiring, I had to do this last week on the mates 90, turned out his wiring going to the sensor was goosed! Hope this helps
 
Check the earth onto the engine. Had this with a kit car and it turned out to be a missing earth therfore using the temperature gauge earth as a return
 
earth strap to engine is good (12mm cable)...it is the same 200tdi engine i had ...the gauge part number is prc7311 and the sensor is prc8593 ...can it be a damaged resistor in the gauge?
 
Airlock mis matched sendors

Does it have a disco tdi engine fitted??

The sender will be wrong if so contact Steve Parker for the correct sender unit.

Be wary there are 2 types or thread and a few types of sendors with varying resistances for certain year of guage.
 
Its disco with thin thread. Spoke to steve parker. I should have right one. Have bought 4 different senders now and same on all.

Going to fit a stand alone i think
 
I've got this on mine (110 van) after working on dash board illumination so need to check earths. Serves me right for cleaning it all up while replacing bulbs & glueing bulb holders etc etc. :-(
 
The gauges take their ground through the body of the gauge! You need to make sure that the gauge bodies are grounded or they read silly amounts and act in a random manner. I installed large O rings around the gauges in order to stop them rotating and it was that that caused the issue. I now have a small cable with 6 small ring crimps and make sure that they are all grounded using that just in case.
 
cowasaki said:
The gauges take their ground through the body of the gauge! You need to make sure that the gauge bodies are grounded or they read silly amounts and act in a random manner. I installed large O rings around the gauges in order to stop them rotating and it was that that caused the issue. I now have a small cable with 6 small ring crimps and make sure that they are all grounded using that just in case.
Click to expand...
gauges work through resistance, the earth been the sender which is variable, earthing the gauge body is only for illumination anything else is coincidence
 
jamesmartin said:
gauges work through resistance, the earth been the sender which is variable, earthing the gauge body is only for illumination anything else is coincidence
Click to expand...

James this is what I've found.... The temperature gauge requires a ground. The input for the gauge is a resistance to ground i.e. the sender is attached to ground and its resistance changes depending on the temperature. The gauge has an input of whatever the voltage is between about 12.6 and 14.5 if it didn't have a ground connection it would not be possible for it to actually work because it needs a fixed ground in order to know where the temp is in relation to it (i.e. both connections vary voltage and ground). If you don't believe me try taking the temperature gauge out of the dash and just connecting the sender and ignition live and see (through its range). Not all gauges require ground, other than for illumination eg power or pressure pipe ones, but ground resistance ones do as they are effectively comparing the real ground to the senders ground.

I had this same fault a while ago, the gauge appeared to work to start with but the temp went far too high. It dropped to the normal level when I attached the ground. I then realised how the gauge worked internally and it made sense. Whilst trying to diagnose the fault I bled the system about 5 times, changed the sender, replaced the wire and borrowed a working gauge. It was only then that I realised (because it worked when the gauges body touched the metal of the dash surround). Once I realised I went back to the original wire and gauge with no issues since..
 
Last edited:
TRYING TO FIGURE OUT TEMP GAUGE PEGGING HOT ISSUES ON A D90 "RESTORED".
PROPER ENGINE AND SENDER FOR '92 200 TDI. BUILDER STATES NEW GAUGE INSTALLED AS HE RECALLS.
STARTS UP RUNS FOR 10 MINUTES GAUGE GOES FROM COLD TO PEGGED HOT. ENGINE TEMP AT SENDER IS 170F.
LOOKING AROUND AND FIND THIS THREAD WITH COWASAKI STATEMENT RE. GAUGE BODY GROUND CAUSING ISSUES.
SUPPLY GROUND TO GAUGE BODY, TEMP SETTELS TO NORMAL!!!
I'VE BEEN DOING THIS FOR 20+ YEARS AND LEARNED SOMETHING NEW AGAIN; TODAY.
THANK YOU SIR FOR THIS POST FROM A FEW YEARS BACK.
ALLEN
 
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