Dashboard engine temperature sensor fluctuating

[JSladen]

Got a slightly weird one here. (Xantia S2 Estate 1.9TD)

When driving along the temperature guage on the dash reads about 85-90 as I would expect, but can then jump up by 5-30 degrees at times. These changes seem to co-incide when high draw electrical items turning on/off (eg. the blower, radiator fans, rear demist and headlights/fog lights etc.) I have had the needle sat firmly in the red before, with no STOP/overheat light on, and when I've pulled over and checked it the engine temp has been fine. None of the other gauges move at all when this happens

Before anyone suggests it, I have checked the thermostat (replaced to make sure), and coolant system (drained/cleaned/bled twice), and there's no excess pressure buildup or exhaust smell from the header tank suggesting a head gasket issue. I've tried a replacement temperature sensor as well, and get a matching results.

I'm figure it has to be an electrical issue somewhere, but I don't know where...

Just wondering if anyone has had this issue before, and has an idea where to look at for fixing it?

[CitroJim]

Yes, a very well-known problem S2 instruments. It will be caused by a bad connection between the gauge itself and the contact 'fingers' it uses to connect to the printed circuit board behind it.

Often the problem can be confirmed by giving the top of the dash a good thump. the gauge is likely to return to normal.

The instrument pod can be dismantled with care and the contact fingers and pads cleaned up. It's not easy and is a delicate job..

Here's a picture of the back of the gauges showing the fingers:



And the back of the printed circuit board showing the contact pads:



This only applies to S2 instruments. S1 instruments are totally different...

[Northern_Mike]

Might I add to this, not wanting to scare anyone - I had this happen with a ZX 1.9TD , a 1994/95 model. Temperature gauge started to fluctuate going up the M6. I ignored it. The waterpump failed and threw the cambelt off.

I would wager on Jim being right in this case though, but...

[addo]

A timely post. My temp gauge hasn't been reading right since I drove through a mother of a puddle in some flash flooding last week. Figure either the alternator's dropped a diode or it's something like you describe above.

[Mandrake]

My temperature gauge does the opposite - it will say 85 or so while on a motorway then suddenly drop to 70 then go back up again. Hasn't done it for a while but it is quite disconcerting...

[JSladen]

Brilliant Reply from Jim, Thank you very much.
I've got a spare S2 dash panel (it has some marks on the front so I don't want to do a straight swap) so I'll have a play with that and figure out the taking it apart process.

I'll keep an eye/ear on the water pump as well just in case.