Coolant Temperature Sensor Misreading

[dangafo]

Hi. I love this car!. Just replaced the sensor, because when I took the car to the garage for another reason (misfiring caused by faulty coils) they found the sensor was faulty too. This sensor was ordered from France, as there were no parts available in NZ. It was done by an official dealer.

 

Today 4 days after replacing it the STOP light came on while on the motorway. The temp gauge was right up and the display showed 'engine overheating'. While I carried on in order to find a safe place to pull over, everything settled (in less than 2 min).

 

Any thoughts on this?

 

Daniel

2004 C5 Exclusive 3.0 V6

[Johndouglas]

Has the electrical connector been replaced correctly?

Maybe the system was bled insufficiently. You may have an airlock.

[paul.h]

If it is like the C3 it may have 2 temperature sensors, one for the gauge and one for high temperature which also sets off the engine fan and warnings. I looked in the Haynes C5 manual but this only shows the one sensor but it does not cover the 3 litre petrol car.

If it does happen again put the cabin heater on full to minimise any damage if it is a real high temperature. I would also make some other checks in case the thermostat is not working properly.

[dangafo]

Thanks for the suggestions. Will try those and report back.

It happened again today. The funny thing is the three times it has happened it's in the cold morning on the way to work, and always on exactly the same stretch of road, roughly 10 km from home.

[paul.h]

You could try with the car parked and the engine running to make sure the engine fan cuts in and to see if it goes to high temperature, also touch the radiator top inlet hose so when it warms you know the thermostat opens. Make sure the radiator is not blocked externally, water pump is running ok. I suspect sensor bad wiring/poor connection (unless by-passing the sensor) may not be the problem since the sensor works by reducing its resistance as it gets warm whereas these may increase the resistance. The French RTA manual for hdi engines gives resistance values for the temp sensor as follows but may not apply to the other engines but you could compare old and new sensors. The hdi high temp alarm is 118°C.

 

DegC / ohms

-----------

0 / 15710 to 16930

10 / 9650 to 10260

20 / 6080 to 6400

30 / 3930 to 4120

40 / 2600 to 2710

50 / 1770 to 1830

60 / 1220 to 1270

80 / 620 to 636

90 / 400

100 / 320.

 

 

This reminds me of the 2 occasions our C3 has gone to high temp in 3 years. Both were on the same journey on 25th December 2 years apart and below freezing outside (the only times this car has made this journey). 1st time in the last 100 yards of the 60 mile trip and 2nd after about 40 miles on the M62 on a hilly bit but still about 70 mph. Lots of checks as above and using a code reader for live data and nothing found wrong after 1st time and 2nd time slowed down and kept the cabin fan on which allowed the temp gauge to be controlled up/down (so the sensor thought the temp was real). For the rest of the 3 years nothing so I have not replaced anything yet but have a new thermostat and sensor ready. The C3 also has a 2nd sensor which on high temp goes to earth and gives the warnings/starts engine fan but it does not look as if the C5 has this.

[dangafo]

Thanks again. I haven't heard from the dealer yet, they are still researching, so this is very helpful.

It hasn't happened again. Weather is less cold (relevant?).

I have been in very heavy traffic and jams, driving in 1st or 2nd gears for 30 minutes or so, and it hasn't overheated. In fact the temp gauge behaviour and reading look pretty plausible all other times. I'll still check the fan kicks in when iddling. Thanks!

[dangafo]

Thought I should post an update on this.

 

The dealer hasn't come up with any possible explanations yet. This is from queries and searches, they haven't seen the car.

 

The problem hasn't happened again.

 

I tried the fan. I had been driving in heavy traffic but the temp gauge never went past the middle. With the car like this when I got to a side road and left it iddling for 5 minutes or so. I couldn't hear the fan (not being very familiar with it), but the temp gauge never went up.

 

From what I read in this dicussion I think I'll probably ignore this for the time being.

[iannez]

as paul said i'mm sure there's 2 temp sensors. a green one and a blue one. the temp gauge will also go right up if the cooling fan is starting to seize or going open circuit.

[dangafo]

Just thought I'd update on this problem.

 

Hasn't happened again at all ever since (almost 2 months). No other issues to report. Enjoying the trouble-free ride like most of us!