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Discussion Starter #1
Anyone know if it’s normal for 1.5 dci to pretty much always run at about 76C? I bought car (2014 model) in August 2019 and noticed, as have others, that temperature gauge sits on bottom reading almost all the time. Very occasionally on a hot day going up a steep hill it will go to mid point but return to bottom reading very quickly. I took it back to Renault dealer thinking stuck open thermostat but told that it was operating normally and they were all like it. It’s bugged me as only getting 48 to gallon which seems lower than it should be? I bought a Bluetooth obd2 reader recently and that shows that the car runs at approx 76C even on a hot summers day. I can get the tempearture to rise when stationary by turning off air con and rev to 2500rpm for a few minutes. After a while temperature rises and at 80C the gauge goes to mid point and at about 82/83 cooling fan comes on. Still wondering if I have faulty thermostat? Any thought?
 

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Super Moderator Technical Supremo Platinum Member
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Open thermostat is easy to diagnose.
Start from cold and keep checking the temperature of the top hose as the engine warms up.
The top hose should not get hot, even warm, until the thermostat opens.
If it seems to be getting hot early, suspect stat.

Having said that, what you are describing seems to me to be an offset (low) to the true temperature reading.
Even though diesels tend to run cooler then a petrol burner, I would expect temps in the 80s and the cooling fan not to come on till the late 80s/early 90s.
That comes back to the temperature sensor reading low.
 

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Discussion Starter #4
Ok test done and thermostat opened at an indicated 75c on the OBD2 readout?
 

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To me the cooling system is working right but providing the wrong reading.
 

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Discussion Starter #6
Thx for feedback appreciate. Is it possible the thermostat is opening too soon though?
 

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Is it possible the thermostat is opening too soon though?
It's possible.
What I don't know is when it should be opening, ie what temp rating it has.
Or what should be in the vehicle.
Most diesels seem to have 81 or 88 degree stats these days.
That means they would be fully open at the stated temp, so it is possible that an 81 degree stat would be starting to open at 75, enough open that you can feel the change in temp.
 

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Discussion Starter #8
I think it’s likely to be 83c from what I am reading. I see what you mean, i thought the 83c figure was when the thermostat opened, did not realise it refers to the fully open temperature. Hmmm, the Renault dealer certainly seemed pretty confident there was no issue. Their head mechanic apparently had same issue with his own Megane mk3, of temp gauge that never went above first position. Read about the dci running cool but just seems strange that Renault would not rectify what appears to be a bit of a widespread issue of gauges not operating normally. Wondering if gauge could be recalibrated?
 

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Discussion Starter #9
Update I bought myself an infrared temp gauge. That confirmed that the readings from the cars temp sensor are correct, measuring off the top hose. The reading was as I expected a few degrees below the obd2 reading, as pipe I am guessing will be slightly cooler than coolant. Thermostat opens at indicated 75c. Left to idle with air con off takes an age to get to 80c when cars temp gauge goes to mid position. Not sure it will even get to 80c with aircon on due to fan. As soon as you start driving the temp falls to 75/76c. I am suspecting thermostat not operating correctly? Any thoughts?
 
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