Xantia Engine Temperature Sensing and Bitron Unit

PeterMann · Unread post by **PeterMann** » 22 Jan 2004, 13:25

Xantia Engine Temperature Sensing and Bitron Unit
Recently had the experience of overheating my 1994 2.0i Xantia due to loss of coolant fluid. Although the temperature gauge is working accurately against the thermostat value, the alarm light in the gauge did not trigger until nearly at 120degreesC. I noticed the light come on (it was twilight) and immediately switched off.
Since then, there is a pressure residue in the cooling system, with gas escaping when the reservoir cap is released even when the engine is fully cold. My interpretation is that a pinhole leak has developed in the head gasket between a combustion chamber and the coolant jacket. The engine oil is unaffected, and the engine runs and pulls as normal (apart from atrocious starting), and the coolant slowly disappears.
This leak indicates that the temperature sensing system on this Xantia failed to protect against warping of the alloy head due to loss of coolant.
Looking for the engine temperature sensor, I do not locate a temperature sensor on the 3 visible sides of the head, but find a possible candidate adjoining the engine oil dipstick. But if this really is the engine temperature sensor, then all Xantias of the same design would be susceptible to expensive engine problems as a result of coolant loss, because as the water drains from the head, the head will be the first engine component that will overheat.
In the head is where the engine temperature sensor should be, so that temperature is monitored at the point which will be first to overheat.
Then there is the matter of the warning light not coming on until normal operating temperature (88 to 93 DegreesC) was exceeded by an extremely large margin. My instinct is that there was some fault in the apparatus which detects and triggers an overtemperature warning light, because with a 20psi relief cap I would anticipate a designed triggering temperature of about 105 degreesC. So, why did my warning light not trigger until 15 degrees above that ?
Is a faulty Bitron Unit a candidate for this discrepancy ?
Is the Bitron Unit a simple passive device, or does it perform complex signal-conditioning functions ?
Is the Bitron Unit (with its reputation for unreliability) serving some uniquely useful purpose, or can it be bypassed with reliable commonplace components ?
Where is the engine temperature sensor ?

alexx · Unread post by **alexx** » 22 Jan 2004, 13:48

Well, relief cap is set to 1.4 bar overpressure (=2.4 bar absolute pressure). At that pressure, water boils at 126.6 deg. C, so I think there's no need to trigger the warning light at 105.

PeterMann · Unread post by **PeterMann** » 23 Jan 2004, 07:41

Running at speed in Australian heat with aircon, running temperature holds steady at 93. I would have though that 17 degrees above the thermostat setting would indicate a substantial shortfall in the cooling capacity.

AndersDK · Unread post by **AndersDK** » 23 Jan 2004, 08:01

Peter -
There MUST be at least 2 separate sensors in the head -
One for the ECU - 2pole connector piece.
One for the overtemp warning lamp - or temp gauge with build-in electronics for the warning lamp - 1pole connector.
I have yet to see these 2 sensors combined into one unit.
I can only agree that any coolant temp sensors fitted in the block would be insane - and this is NOT the case on Citroen engines.
The sensor you found near the dipstick is for any oil gauge - being level or pressure.
As you know from your BX - there are 2 each 1pole sensors for the warning lamps - one of these would be extinct in favor of a 2pole sensor for later injection fitted BX'es.
They should be found near the thermostat housing - i.e. at flywheel end of top - known to have moved around a bit on various generation Citroen engines.
BTW your radiator fitted coolant level warning did not work ?
PS : You're aware that recently the Czek site added info on the Xantia aircon ? :
http://citroeny.cz/servis/xantiaser/klima/klima.htm

PeterMann · Unread post by **PeterMann** » 23 Jan 2004, 18:34

Coolant level warning never showed. Thanks for reminding me that this is probably out of action. Yes, oil sensor. OK, tomorrow will try viewing concealed parts of head with torch and mirror.

JohnCKL · Unread post by **JohnCKL** » 24 Jan 2004, 12:24

"BTW your radiator fitted coolant level warning did not work ?"
Anders, I don't think my 96 XTD comes with the device. Is it the sensor on the cap of the coolant spare tank? I don't have the sensor, just the cap but I can buy a sensor and the wiring is in place. Where does the warning light show up? My manual doesn't indicate where the warning turns up either. Is it possible to install it? Thanks.

AndersDK · Unread post by **AndersDK** » 24 Jan 2004, 14:17

I checked with Haynes Xantia electric schematics -
According to the legend for the coolant temperature/level warning circuit - there is no sensor fitted in the radiator (other than the fan thermoswitch).
Instead you have near the thermostat housing a combination sensor fitted : a level warning switch & temperature sensor for the gauge.
This is in fact a 2pole sensor.
- not to be confused with the ECU engine temp sensor.
On turbo diesels an extra separate over-temperature warning switch is fitted - but where this is located is not clear from the legend.
I don't know how to interprete "level" from this legend [:o)]
It could be "warning level" for the temperature - or low coolant level.

JohnCKL · Unread post by **JohnCKL** » 25 Jan 2004, 08:13

Thanks Anders. I thought there could be a coolant level sensor next to the coolant expansion tank filler cap in newer cars. Saw it in a newer XTD but the wiring was not plugged in. The mechanic said the wiring can't be plugged in as the car will show the stop sign. Was confused whether its meant to be a coolant level sensor at all.

LFY · Unread post by **LFY** » 24 Jan 2016, 08:23

I measured my ECU (green) coolant temp. sensor with ohm meter.
@ 21 °C the resistance was 2450 ohms.

Citroen says it should be 2500 ohms @ 20 °C.

So, is my CTS faulty? Should i replace it?

Unread post by **xantia_v6** » 24 Jan 2016, 08:36

You only have a 2% discrepancy, which may be partly explained by not measuring at 20°C, so I don't think you have a problem there.

BTW, you have replied to a topic which is more than 10 years old!

Clogzz · Unread post by **Clogzz** » 24 Jan 2016, 08:40

No, that's close enough.
About 2000 Ohms when cold and 3500 Ohms with a hot engine.

LFY · Unread post by **LFY** » 24 Jan 2016, 08:54

BTW, you have replied to a topic which is more than 10 years old!

Because i didn't want to create a thread for just a simple question.

I also measured the instrument cluster coolant temp. sensor. The blue one that has only one terminal.

@ 21 °C it's resistance was 2863 ohms.

Is it faulty?

About 2000 Ohms when cold and 3500 Ohms with a hot engine.

They are NTC type sensors. When engine gets hot, their resistances go lower.

@ 20 °C = 2500 ohms
@ 90 °C = 230 ohms

French Car Forum

Xantia Engine Temperature Sensing and Bitron Unit

Xantia Engine Temperature Sensing and Bitron Unit

Re: Xantia Engine Temperature Sensing and Bitron Unit

Re: Xantia Engine Temperature Sensing and Bitron Unit

Re: Xantia Engine Temperature Sensing and Bitron Unit

Re: Xantia Engine Temperature Sensing and Bitron Unit