Running Cold, Temperature Gauge or Something else

[JPB]

Hi,

I know it has been cold of late but one of the megs has been feeling it too.

The engine temperature gauge is taking much longer than usual to come up to the normal running temp ( about the third indicator). Nothing much wrong there on cold mornings and going slower than normal due to snow etc, but even then it seemed far to long for it to come up to temp.

The next strange thing is that the other day when sitting in traffic the temperature gauge fell back to zero, and then rose again when I set off. Outside temp was about 5C. Over the next fews days the temp gauge has been pretty much following my driving speed. If I go 50+ is fine but any less the gauge starts to fall, (30mph second indicator, in traffic first indicator) when it falls the car becomes sluggish, just as if it were cold/just started. I've never seen a car do this before and as we have two megs, the other one doesn't do it. The car should get to temp and stay there, for best running etc. At first I thought that maybe the cooling fan wasn't switching off, but when I checked it was not running, so at a bit of a loss.

Has anyone seen this before? and is it just some electrical gremlins or something more alarming?

[AlexB]

"...the gauge starts to fall..."
Electrical gremlins tend to be either on or off, and you have a gradual transition... Thermostat?

[silencer51]

What AlexB said. The thermostat may be stuck.

But I wouldn't rule out the instrument panel...

[AlexB]

The instrument panel cannot cause poor running.

[silencer51]

The instrument panel cannot cause poor running.

I must pay more attention when reading posts...

[silencer51]

Also, on the Meg II there is no thermostat - there is an engine coolant temperature sensor that screws in the right side of the engine.

This give the necessary temp info to the ECU which in turn manages the injection system.

If it reads the coolant as cold then more fuel is pumped into the cylinders and the timing is retarded.

Its cheap to replace...

[YoungTurk]

Hello JPB

Something similar happened to my daughter's Megane (03 reg) some time ago. I swapped cars with her (we are named drivers on our insurances) and drove her car for few days to experience the problem myself. Whenever I felt a slight hesitation in engine power driving between 60 to 70 mph I noticed the temperature gauge rapidly falling to zero, staying there briefly before slowly rising back to normal temperature! Happened, maybe once a day. Our dealer (eventually) agreed to keep the car for a week to see if they could resolve the problem. It turned out to be something to do with the "oxygen level detector" for the catalytic converter! I suspect the engine management unit was getting confusing feedback and was over-compensating for something not really there... I thought this may be of some use.

[AlexB]

No thermostat?
Retarding timing to keep it warm in winter?
If such, then, for example, what is the part number
8200112054 in F9Q-800 or
7700872554 in K4M(J,R), etc. ?

8200112054:
https://www.bt-autoteile.de/shop/product ... 08_342_344
7700872554:
https://www.piecesauto-tuning.com/boutiq ... 008-89.jpg
https://www.bt-autoteile.de/shop/advance ... 700872554+

[silencer51]

Hmm... I think we are talking about the same part, but we give it different names (the price seems right)...



When the ECT sensor fails it sends bogus data to the ECU, i.e. engine coolant at 0 degrees when its at 80 degrees. The ECU in turn is tricked into 'cold-start' mode, i.e. richer fuel/air mixture and different timing. This could be the cause of the hiccups.

Either way its not an uncommon fault on this model or on Renaults in general - at least thats what I've heard from my dealer.

The O2 sensor is also not an uncommon problem, but I really don't understand what the engine coolant temp gauge would have to do with it!

[YoungTurk]

Well, yes, I agree it sounds strange. However, who knows how these things may be interconnected in today's complex machines (except the designers?); quite a lot of the control is done in software which processes information from many sensors. Anyway, whatever they had done seemed to cure the problem.

[AlexB]

silencer51,

The thermostat is not indicated in your drawing. It is shown in PR->Upper_Engine->Pump section. In some engine models it is called something like Assy/smth. Nevertheless, the assembly contains a regular thermostat inside.

On the second point you are absolutely right. If the ECU "thinks" that the engine is cold, it goes into the warming-up mode. This may happen in case of the thermo-sensor failure.

I don't understand the story with the O2 sensor either. Most likely, it is the case when the dealer started changing parts at random, blaming their own incompetence on the manufacturer and asking the customer to pay for it.

[YoungTurk]

Sorry, I did not explain myself properly. In our case, the problem was not showing when running cold. It was while driving at speed, at optimum temperature, a slight loss of power, car slightly jerking and the temperature gauge temporarily going down to zero and slowly coming up to normal again. It is this latter behaviour which was attributed to the oxygen sensor. I originally responded in case this may have been useful, but it is now apparent that it was not. My apologies.

[AlexB]

YoungTurk,

Your information is relevant and interesting indeed, so please stay around.

I just don't know how to interpret it. What do you mean by "slowly coming up to normal again"? Once it started rising, did it take seconds or several minutes to reach the normal value? If seconds, then it is the temperature sensor, othervise it is the thermostat or something else. In any case I don't see how the O2 sensor can affect the dashboard readings.

[JPB]

Thanks everyone for the comments. I must admit I didn't think the meg II had a thermostat either but just goes to show. Thought thermostats were a thing of the past. It looks like it could be a combination of thermostat or one of the sensors. The mpg is down on normal too suggesting that it is in 'cold start' mode all the time.
Spoke to the local dealer and with wisdom told me that it shouldn't be doing that. Think we had already sussed that out.

[bgray]

I posted this one in Nov:
Temperature Gauge drops off engine then sluggish then dead



Did you ever get it sorted?

Thanks in advance.