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Today, I was driving my mum's car, a Citroen C3 1.4 HDi from 2004, and I noticed that the coolant temperature was rising very slowly. Just as a reference, this is what the dashboard looked like (picture from different car, but for my purposes here this is not an issue; coolant temperature reading was exactly the same as in the picture below):

Dashboard

It actually never went up after one block, even after driving a significant distance. If this coolant temperature indicator is designed like all the others I've ever seen, you'd expect the indicator to be in the middle (i.e. three blocks out of six, approximately).

This would lead me to think that the car did not reach proper operating temperature and that the thermostat is most likely malfunctioning and stuck in the open position. However, she said that she mentioned this exact observation to a mechanic and that it's "not an issue" and that it's "normal for the indicator to not rise after one block", so she doesn't believe me. This, however, makes no sense to me at all. If all of this were true, there would be no way to know anything about the coolant temperature until it is at operating temperature, yet there are five blocks left to indicate overheating (out of which only two are red). This just doesn't make any sense to me.

I wanted to use an OBD2 scanner to get the temperature reading, but this car has a non-standard connector so I couldn't do that (I can of course buy the right part but that might be a bit overkill for something like that). Maybe I could use probes to measure the temperature, but I don't really like working near potentially hot coolant.

So, actually, the core question is very specific: is one bar out of six indicating operating temperature in this car? Again, I highly suspect that this is not the case, but since a mechanic told her otherwise, I'd like to get confirmation.

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  • Not related, but since you have an OBD-II scanner, please consider contributing data to The Great MAF Experiement. Thanks!
    – Zaid
    Dec 24, 2016 at 19:01
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    The most common reason for a user to really care about the temperature is if its too high, so it doesn't seem that out there for normal to be at or below one bar. What does the owners manual say about it? Why dont you also give a couple dealer service departments a call and ask about the gauge behavior?
    – Jason C
    Dec 24, 2016 at 19:43
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    @Ben I meant, contact the dealer and just ask what the normal behavior is, without going into your specific concerns. Hope being that one of the service techs just happens to know, doesn't hurt to ask.
    – Jason C
    Dec 24, 2016 at 22:41
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    @Ben I have no knowledge of this make in particular. But, it has been customary for temp gauges to read just under half gauge at thermostat open temperature (around 180 deg F) and at or slightly over half at fan on (200 to 210 deg F) temperature. This would translate into 2 or 3 blocks on this "gauge". This was done because owners perceive 1/2 gauge as "normal". A scanner is the appropriate tool to test coolant temperature.
    – Fred Wilson
    Dec 25, 2016 at 0:57
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    If you want to get an approximate coolant temperature without safety concerns or buying an expensive adapter or paying for diagnostics, pick up one of those $30 infrared thermometers. You can get a good idea of the engine water temperature from the temperature of the inlet hose, and you'll find plenty of other uses for it (checking manifold temps, checking whether the grill is ready, etc.)
    – barbecue
    Dec 25, 2016 at 1:46

2 Answers 2

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I don't have a C3 Picasso, but can see plenty of Google images which show the temperature indicator is at 3 bars out of 6.

Image 1

Lumina SS Cooling Fans

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    And these people weren't talking about overheating issues? :)
    – Ben
    Dec 24, 2016 at 18:56
  • @Ben one of them is complaining about the temperature lights staying on (not sure what that means). The other is asking about the CEL I think
    – Zaid
    Dec 24, 2016 at 18:59
  • Those don't look like the 2004. They very well could have changed the dashboard UI.
    – Jason C
    Dec 24, 2016 at 19:37
  • @JasonC They do, actually. The only clearly noticeable difference is the gear indicator and the different layout for the rev counter in the second picture.
    – Ben
    Dec 24, 2016 at 19:43
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    @Ben Unless they changed it because too many users were concerned about the 1 bar, lol.
    – Jason C
    Dec 25, 2016 at 0:40
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I'm pretty sure that you're right – the gauge needs to be able to show both low temperatures as well as normal and hot.

That said, it makes sense to see if you can figure out what's wrong. If you had an OBD scanner that you could attach that would be the easy to way to sort this out, but since you don't one way to approach it is by checking the heater output. If you're getting plenty of hot air the problem is probably not with the thermostat but with the temperature sensor. It may have failed and be reading low.

That may be "not a problem," as the mechanic said, in the sense that the car still seems to be functioning normally, but it is most definitely a problem in the sense that your mother won't be getting any warning of a problem if one does develop. Also, the ECU may be using the same sensor to determine operating parameters for the engine. You're right to want to pursue it.

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