[Engine] Overheat and antipollution?

[mikeB]

I was 20 minutes into a 50 mile journey in my 2005 2.0HDi Multispace (M59). The multi function display beeped and the message "High Engine temperature" (or something which meant the same) came up. I checked the temperature gauge and in the space of 5 seconds it went up from where it normally is to end of scale. The word STOP also appeared on the dash instrument. I did stop and checked the coolant level. It was normal. I got back in the car and everything was back to normal. Because I had a minor problem the previous day (the headlights stayed on when I turned them off - a further on and off and they were extinguished) I guessed the BSI needed to be reset.

I carried on, as I was some miles from home, and the same message came on a couple of times, again accompanied by the temperature gauge rising rapidly but then falling to normal within a few seconds. The engine ran completely normally. After about a further 20 mins the message did not appear again and I completed my journey, some of which was at 60 mph.

On the way home, again, after about 20 mins, the same message, but it was followed by "antipollution fault". Again the rapid rise and fall of the gauge. This happened a couple of times on  the way home. In addition the yellow engine symbol was lit. Everything seemed to be normal, no excessive heat, smell etc. I watched the temperature gauge closely and noticed that the gauge did seem to vary a little, between perhaps 75 and 85 degrees C, possibly a little lower than is usual. I know these gauges are not that accurate but it is normally rock steady. I suspect the thermostat may possibly be stuck open and/or closed. If it sticks closed the temperature will obviously rise - but so quickly? - Within 5 seconds?. Then, if it opens and sticks open, the engine will be overcooled and so the anti pollution system might kick in.

Tomorrow I will reset the BSI but would appreciate any advice. Is it best to simply replace the thermostat? Is it an easy job?  Has anyone else had this problem? All comments welcome.

[cancunia]

It might be a faulty temp sensor / transmitter. Not sure how that would give you the Anti Pollution message though, Anti Pollution can be a number of things, do you have a code reader?

[mikeB]

It might be a faulty temp sensor / transmitter. Not sure how that would give you the Anti Pollution message though, Anti Pollution can be a number of things, do you have a code reader?

Thanks for the comments. I agree it could be a faulty sensor as I don't think a jammed shut thermostat would make the temp gauge rise so quickly.

I have a Chinese Lexia but have not used it for a while. I will see what I can do.

Thanks again

[mikeB]

It might be a faulty temp sensor / transmitter. Not sure how that would give you the Anti Pollution message though, Anti Pollution can be a number of things, do you have a code reader?

Did a BSI reset this morning. The engine warning light was not extinguished so I pressed my Lexia into service. It showed code P0116 which is Engine Temp not normal range. I think the problem is possibly the temp sensor or a short or open circuit to that device. Its so cold here currently I am not planning on spending time on this until it gets warmer, but any advice/ comments etc are still very welcome.

[cancunia]

At least the code is consistent with your temp readings. Maybe disconnect the sensor and see what the gauge reads when you have the engine warm. Is the gauge at zero when the engine is cold?
I'm totally guessing here, but if the sensor decreases resistance as it gets warmer (?), maybe you can do a controlled short to ground with an extra piece of wire and see if the gauge moves. A multimeter would be helpful to check my guess. Lexia may be able to tell you the coolant temp, Torque via an OBD adapter certainly will.

[mikeB]

At least the code is consistent with your temp readings. Maybe disconnect the sensor and see what the gauge reads when you have the engine warm. Is the gauge at zero when the engine is cold?
I'm totally guessing here, but if the sensor decreases resistance as it gets warmer (?), maybe you can do a controlled short to ground with an extra piece of wire and see if the gauge moves. A multimeter would be helpful to check my guess. Lexia may be able to tell you the coolant temp, Torque via an OBD adapter certainly will.

Thanks again for your helpful comments. The gauge does read zero when cold, and yes, the sensor is a negative temperature coefficient (NTC is much easier!) resistor, so your idea of simulating it is a good one and should prove it's the sensor. It will be a way of "kidding" the BSI that all is normal. I just have to use the right resistor.

The thought also occurred to me that of the 2 wires leading to the sensor one is the feed from the BSI and the other goes to ground somewhere. An intermittent ground could produce these symptoms. 

I would have done some of this yesterday but it was so bitterly cold, even in the garage, I didn't have the will to do it!

I will post what happens. I need to sort this and remove any doubt that the engine temperature is wrong.

[mikeB]

At least the code is consistent with your temp readings. Maybe disconnect the sensor and see what the gauge reads when you have the engine warm. Is the gauge at zero when the engine is cold?
I'm totally guessing here, but if the sensor decreases resistance as it gets warmer (?), maybe you can do a controlled short to ground with an extra piece of wire and see if the gauge moves. A multimeter would be helpful to check my guess. Lexia may be able to tell you the coolant temp, Torque via an OBD adapter certainly will.

Thanks again for your helpful comments. The gauge does read zero when cold, and yes, the sensor is a negative temperature coefficient (NTC is much easier!) resistor, so your idea of simulating it is a good one and should prove it's the sensor. It will be a way of "kidding" the BSI that all is normal. I just have to use the right resistor.

The thought also occurred to me that of the 2 wires leading to the sensor one is the feed from the BSI and the other goes to ground somewhere. An intermittent ground could produce these symptoms. 

I would have done some of this yesterday but it was so bitterly cold, even in the garage, I didn't have the will to do it!

I will post what happens. I need to sort this and remove any doubt that the engine temperature is wrong.

[mikeB]

Tried to remove the green temperature sensor plug but can't work it out - nothing to press as far as I can see. Help appreciated.

[cancunia]

According to this, there's a metal retaining clip (part 11)?

https://www.catcar.info/citroen/?lang=en...aWVyPT0%3D

[mikeB]

Many thanks for the link. It might well be useful. My problem is not how to remove the sensor, but the electical connector plug. It's 2 pin and coloured green. It seems to have some mechanism which stops it falling off. My problem is I can't see how I overcome this mechanism. I assume it's something to press, but I can't fell anything with any "give" in it. I am quite used to these types of connector but this one has beaten me.