Inaccurate Temperature Gauge

Hi All,

2002 M13A Jimny

Any help would be greatly appreciated -
Temperature gauge on dash displays overheating once car is up to temperature. I have installed an aftermarket temperature sensor on upper coolant hose to verify that it isn't actually getting too hot (hovers around 90C). 

Have replaced ECT sensor and checked all wiring to and from dash/sensor/grounds. Sensor has resistance of approximately 55-60 Ohms when at 90C - this also matches a test with the sensor out of the car in a pot of 90C water, along with the 50C test in the service manual.

However, as a test, when swapping out the sensor for a normal resistor of equal value, 55 Ohms, the gauge shows a normal temperature half way up. 

I'm getting just over 14V to the fuel gauge's positive terminal, as well as a solid ground and sensor connection. The output from the gauge to the sensor is around 12V with engine running. 

Weirdly, the gauge will display correctly with the car not running - it will start to rise slowly from middle position to hot after a few seconds when I hear a relay kick over and the power to the back of the gauge climbs from 12V to 14V. 
It will also display correctly if the dash is independently powered from a separate 12V source (10V to sensor). However I don't see any form of a voltage regulator on the wiring schematics to indicate the dash should only be seeing 12V at all times. 

Once again - any help would be greatly appreciated.

The actual pointer on the gauge is possible to put on there in the "wrong" position. you could take a look at a dash picture from another 2002 Jimny and see if yours is off.
www.bigjimny.com/forum/8-my-jimny/61472-...kuza?start=84#203590
Here you can see when I swapped clusters (for a totally different reason) how the temp gauge and the other pointers got a bit off on the lower picture. Or they where off on the upper picture, I dont remember. Moved them around a bit on the old dash I think, but anyhow they work fine now.

is the temp. gauge needle meant to sit off the scale when the engine is cold then?

From memory yes. I now have illuminated bars on mine.

The lower picture with the low mileage dashboard is the one I havent fiddled with. It came out of a breaker car so might have been fiddled with before I bought it, but not very likely.
I would look at pictures of dashboards of the same year/model and put the pointer back at approx the correct place.
And maybe not think too much about it and, if the car works fine otherwise and do not loose coolant I would sleep well at night too.

btw now the same 40000km dash says 105000km. 65000km since 2019. plus the 112000 it had up to then ouch, my car is getting geriatric.

I agree with the advice above and will just add that the gauge needles are attached to little motors that sometimes develop "personalities" over time.  A little bit of crud or just random entropy can affect how the motor reacts to the instructions from the ECU. 

Other elements on the circuit board (capacitors, resistors, etc) can fail too, and unless you are set up to diagnose and repair surface-mount components, replacement of the whole assembly is the only real option.  It may be prudent to pick up a secondhand instrument cluster if one comes to your notice, in case of total failure.  (But I am not sure how this affects mileage readout on a Gen3, or how your MoT rules deal with that.)

yakuza wrote:

ouch, my car is getting geriatric.

Hmm, time to haul out one of the major assemblies and rebuild it on the kitchen table over the weekend, perhaps.