1.9TD overheat warning - real or spurious?

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Richard_C
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1.9TD overheat warning - real or spurious?

Post by Richard_C »

The Synergie has a temperature gauge and (as I now know) a warning light. The gauge normally reads just above 70, goes up to 90 in hot traffic jams and grinding up long hills.

Yesterday it went up to about 85 in a traffic jam in London, the second fan kicked in as it should, and when I got rolling again the gauge came back down to its usual 70+. All fine on a fast motorway run after that, then on the last few miles home, open country road doing about 55 on the easiest flattest bit of the day, the "STOP" and red warning light on the temp gauge came on. But, the temperature was just where it had been most of the day, a little over 70. Backed off a bit for a couple of miles and the light went out, cycled through that same sequence twice, then after a few more miles went out and stayed out so I got back up to normal velocity. The gauge read the same throughout. Today had a look, water level normal, no signs of anything untoward.

Might be a real problem, might be a duff sensor. Does anyone know how the temperature gauge and temperature warning light are set up on the 1.9TD ? Separate sensors? Different places measuring different things? Any views welcome.
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Re: 1.9TD overheat warning - real or spurious?

Post by Old-Guy »

I remember a post on just this subject (1.9TD Xantia admittedly) not that long ago. IIRC, the XUD9 has separate sensors for gauge and warning light. Your problem might be a failing thermostat (no longer opening anything like fully); when was it last changed? In my experience, they need changing every 5 years or so.
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Re: 1.9TD overheat warning - real or spurious?

Post by CitroJim »

Yes, indeed Guy, certainly in the Xantia the warning light and gauge run from different sensor and again in the Xantia, the often held cause of this is the brown Bitron sensor or the connections to it.

The Bitron sensor is failsafe as if it fails open-circuit it will bring the fans on and light the warning light... An open-circuit can be caused by bad connections and it's not unusual for a bit of coolant to get on the plug.. It's worth popping it off the sensor and giving it a clean.

One good thing is that it's 99.99999% likely it's an electrical problem rather than a real problem with the cooling.
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Re: 1.9TD overheat warning - real or spurious?

Post by isisalar »

On my Xantia the red warning light on the temp gauge sometimes comes on and stays on when the car is started, I was told it comes on when the coolant level is a bit low. A blip of throttle extinguishes it for me, it could be your level is a little low.
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Re: 1.9TD overheat warning - real or spurious?

Post by Richard_C »

Thanks all. This is making good sense, and its useful to know that there are 2 sensors and that the bitron sensor fails 'open circuit' - could explain a lot. I was pretty convinced that it wasn't a real cooling issue - no sign of head gasket problem and the water pump replaced at the same time as the cambelt around 10k miles ago.

I have had a quick look - water level is fine - there is a sensor of some kind on the header tank near the filler, and two inserted just above the thermostat body. I don't have time today for any serious work but will get a meter on them when I can. I think there is something to do with fast idle when cold which might be one of them. They look nice and dry but at 17 years old corrosion may be present in the connectors - last year I had what seemed to be a cps failure but a simple wire-wiggle put it right.

If it is the thermostat, I think the Synergie packaging engineers must have made a mistake. For some reason they have made it both visible and very easily accessible with plenty of room to get a 1/4 inch or even 3/8 drive socket onto the bolts. :-D

(on my wife's C3 3 pot petrol, I can hardly work out which bit is the the engine)
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Re: 1.9TD overheat warning - real or spurious?

Post by CitroJim »

The sensor on the header tank Richard, is the level sensor...

The two you are interested in is the blue one and the brown one on the thermostat housing. The brown one is the Bitron Sensor and the blue one the gauge sender...
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Re: 1.9TD overheat warning - real or spurious?

Post by Richard_C »

Thanks again for that. I remember my early BX had a troublesome level sensor. I do have a thin Evasion/Synergie manual, "Revue practique de technique automobile". Its all in French which I can just about cope with except the wiring diagrams which are unfathomable badly printed block diagrams.
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Re: 1.9TD overheat warning - real or spurious?

Post by Zelandeth »

Not meaning to hijack a thread, but a question I'd been meaning to ask for a while regarding the level sensor on the header tank. What does it do - specifically on the Xantia (S2, 1.9TD XUD9TE engine) which doesn't have a dedicated low coolant level light? Does it just light the red dot on the temp gauge? ...or does it do nothing at all? ...doesnt seem to be mentioned in the handbook...seems daft to have a level sensor but no display device attached to it.
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Re: 1.9TD overheat warning - real or spurious?

Post by CitroJim »

It lights the the STOP light Zel...

You sure the S2 does not have a low coolant lamp? I must look at an instrument cluster I have in my stash to see. Got me thinking now!!!

The sensor is just two prongs that measure the resistance of the water they are in contact with. If the resistance goes high the sensor assumes it's prongs are out of the water...
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Re: 1.9TD overheat warning - real or spurious?

Post by falling-out-with-my-car »

I had a problem with the Xantia over heating in traffic it was boiling over from the header tank yet the temperature gauge was registering 90 degrees and the fans were running fine.
it all turned out to be a faulty header tank cap. I got and OEM one from Wilco's car mart for 3 quid the citroen equivalent which is exactly the same was 29.99
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Re: 1.9TD overheat warning - real or spurious?

Post by Zelandeth »

Played exactly that game with my Skoda - which is what I reckon resulted in the head gasket getting cooked. It would behave perfectly until you put it under full load for more than a few seconds (i.e. climbing a hill), at which point it would then boil, which then caused the waterpump to become air-locked, stopped the coolant circulating...you get the idea. Changing the cap immediately got rid of the boiling problem, but sadly the damage was already done, and I reckon was before I even got the car. Sorting that out is going to be one of my winter projects by the looks of things. At least I have a garage now, thank goodness!
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Re: 1.9TD overheat warning - real or spurious?

Post by Richard_C »

Just to update.

Using the useful information here (thanks) about which connector is which, I took all 3 connectors off including header tank level, gave them a good clean with toothbrush and contact cleaner and reassembled. No repeat of warning lights. I've not had a proper long hot trip since, but I live in hope.

The wire clips which hold the connectors on are so much easier to deal with than the plastic tabs on newer connectors - you can see them for a start.
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