erratic temp and fuel gauges

[chris b]

I've a 97MY 9000 Anni.   The temp gauge was reading very low and jumping around occasionally, including to zero (which put the cooling fan on) so I changed the temp sensor on the side of the engine.  That's stopped the zero readings, but the gauge remains erratic.  It generally shows just above the cold "blue" segment, but sometimes jumps up to a normal reading for a while before dropping back down again.  I've also noticed the fuel gauge reading low in sympathy! 
I've heard this may be a fault with a voltage stabliser in the instrument binnacle.  Grateful for any ideas of what it looks like and/or any suggestions for a fix for the problem.  Many thanks

[Paul @ Kippen]

chris,

I think I just answered this on another forum.

Paul @ Kippen.

[Audax]

Might it be useful to c&p the reply onto this forum too? If the other forum disappears then it may be useful to have the answer here too... Would prevent things like https://xkcd.com/979/ 

[chris b]

I've cut and paste the reply below so others with similar problems can see it.  Thank you for your help.  I'll look over it at the weekend.  Just bought a new thermostat so will try that first before attempting to take the dash apart...

   
    This could be a number of things. If we believe that the problems are linked then I'd start looking for a poor earth conection around the instrument binnacle or perhaps a loose edge connection on the circuit boards thereon. Either requires the top of the dash to be removed. Do a search to identify where all the hidden fixings are and don't drop the 5mm washer up near the speaker on the driver's side.

    Next. The temperature gauges are well known for erratic behaviour. It stems from the design which inputs the measured value from the sensor to the ecu which then outputs what it thinks you need to know. In other words, it sits moore or less in the middle unless things go seriously wrong when it swings widely so that you notice it. Looks to me like you have a failed thermostat.

    The fuel gauge could be a poor connection at the tank ( there is an inspection hatch in the boot under the floor) or have you checked that the setting is giving you mpg rather than litres per 100km.

    Paul @ Kippen.