Citroen C3 2002 1.4 petrol overheating (or not?)

[kyrpousin]

I bought a Citroen C3 2002 1.4 model used in 2020 and almost ever since I bought it it has been saying it's overheating.

The temperature on dashboard is on 3 (middle-yellow) and suddenly goes on 5 (top-red) without passing from 4. After 1-2 minutes the temperature drops immediately to 3, again not passing from 4. If I remember correctly when the indication goes to 5 I start hearing the fan spinning and when it drops to 3 I don't hear it. 

It happens mostly when stopping on red lights or generally stopping but there are times it happens randomly and also both in winter and summer. 

Two mechanics said that the problem was (probably) a temperature sensor and that it's nothing serious but change it sometime.

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.

It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 



So which temperature sensor is it? The blue or green one? Could it be the thermostat? 

After fixing the radiator the mechanic said that the cooling fan didn't always work as expected but the other mechanic said he can't find a problem. 

He also suspected that the car might have a broken head gasket because the coolant tank had some black things at the bottom (meaning that it's oil from the engine) but we didn't really believe that because it doesn't have any other indication of that and the things at the bottom were probably dirt from the cooling system or from the water, or fluid. 

I thought that maybe the sensor that opens the fan on full speed (I think blue) is working correctly but the green one (temp management sensor) is broken, but that is only my speculation. 

[PaulC5]

A common problem. Since the temperature sensors are cheap I would just replace them both. Something to read viewtopic.php?t=89004

[ozvtr]

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.

It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 

Can you clarify this statement? If you have an ACTUAL boil over of coolant, that's a genuine problem. That's not a sensor failure.

He also suspected that the car might have a broken head gasket because the coolant tank had some black things at the bottom (meaning that it's oil from the engine) but we didn't really believe that because it doesn't have any other indication of that and the things at the bottom were probably dirt from the cooling system or from the water, or fluid. 

Head gasket failure is a potential problem. But in the 1.4, typically it's the other way around. An over temp event causes head gasket failure. Head gasket failures in the 1.4 usually causes oil in the coolant or coolant in the oil. This manifests itself as "chocolate milkshake" on the dipstick, oil filler cap, or in the coolant expansion tank.
There is a black baffle in the bottom of the expansion tank and a small build up of "crud" is not unusual. If he thought it was oil, oil is lighter than water (coolant) and will float to the top.

I thought that maybe the sensor that opens the fan on full speed (I think blue) is working correctly but the green one (temp management sensor) is broken, but that is only my speculation. 

The radiator fan is run by the engine ECU. The engine ECU gets it's engine temp from the green sensor.

I'm a little concerned here. On one hand you have all the earmarks of a failing sensor, but on the other you have had an actual boil over event!
First up, I would make sure the radiator fan actually works...and works as advertised! If you have air conditioning, turning it on should cause the the fan to run. Maybe fast, maybe slow...but it should run.
If you don't have A/C, idling the engine, from cold, the fan should come on at least once within 15-30 minutes. And the temp should remain at 3 bars.
Another test is to idle the car and remove the electrical connector from the GREEN temp sensor on the thermostat housing. Within 20 seconds the fan should run at FULL speed.

DO YOU HAVE AUTO AIR CONDITIONING? Failure of the radiator fan will bring on all the temp lights but the fan will not run! I have personally been caught out by this one! Initially it looks like a harmless sensor fault. No over heating in the engine bay, no nothing. So you ignore it ("I'll get to it later"). But after half an hour in stop start traffic...steam from under the bonnet! Here my knowledge (or my fat head) worked against me.

[kyrpousin]

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.

It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 

Can you clarify this statement? If you have an ACTUAL boil over of coolant, that's a genuine problem. That's not a sensor failure.

He also suspected that the car might have a broken head gasket because the coolant tank had some black things at the bottom (meaning that it's oil from the engine) but we didn't really believe that because it doesn't have any other indication of that and the things at the bottom were probably dirt from the cooling system or from the water, or fluid. 

Head gasket failure is a potential problem. But in the 1.4, typically it's the other way around. An over temp event causes head gasket failure. Head gasket failures in the 1.4 usually causes oil in the coolant or coolant in the oil. This manifests itself as "chocolate milkshake" on the dipstick, oil filler cap, or in the coolant expansion tank.
There is a black baffle in the bottom of the expansion tank and a small build up of "crud" is not unusual. If he thought it was oil, oil is lighter than water (coolant) and will float to the top.

I thought that maybe the sensor that opens the fan on full speed (I think blue) is working correctly but the green one (temp management sensor) is broken, but that is only my speculation. 

The radiator fan is run by the engine ECU. The engine ECU gets it's engine temp from the green sensor.

I'm a little concerned here. On one hand you have all the earmarks of a failing sensor, but on the other you have had an actual boil over event!
First up, I would make sure the radiator fan actually works...and works as advertised! If you have air conditioning, turning it on should cause the the fan to run. Maybe fast, maybe slow...but it should run.
If you don't have A/C, idling the engine, from cold, the fan should come on at least once within 15-30 minutes. And the temp should remain at 3 bars.
Another test is to idle the car and remove the electrical connector from the GREEN temp sensor on the thermostat housing. Within 20 seconds the fan should run at FULL speed.

DO YOU HAVE AUTO AIR CONDITIONING? Failure of the radiator fan will bring on all the temp lights but the fan will not run! I have personally been caught out by this one! Initially it looks like a harmless sensor fault. No over heating in the engine bay, no nothing. So you ignore it ("I'll get to it later"). But after half an hour in stop start traffic...steam from under the bonnet! Here my knowledge (or my fat head) worked against me.

Thanks for your reply,
Yes it was probably an actual boil over of coolant or it was the radiator going boom because it's old.

What I thought and some friends told me is that maybe this happened because the sensor was broken so the car fan didn't open because of the sensor or the engine didn't manage the temperature good enough because of the sensor.


For the head gasket issue, there isn't any brown-or white residue neither on the filling cap or the dipstick. The only place where he said was something like oil was in the coolant tank and it was some blackish things stuck on the bottom, the mechanic cleaned it a bit after changing the radiator.

Thanks for the ideas to find the problem.
Also yes I have auto air conditioning but for 1 year now the cold doesn't work as good as it used to. In the first years of the car when you opened the cold the car was going ice, now it doesn't do it that good but maybe that is another problem and not the temperature problem.

[kyrpousin]

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.

It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 

Can you clarify this statement? If you have an ACTUAL boil over of coolant, that's a genuine problem. That's not a sensor failure.

He also suspected that the car might have a broken head gasket because the coolant tank had some black things at the bottom (meaning that it's oil from the engine) but we didn't really believe that because it doesn't have any other indication of that and the things at the bottom were probably dirt from the cooling system or from the water, or fluid. 

Head gasket failure is a potential problem. But in the 1.4, typically it's the other way around. An over temp event causes head gasket failure. Head gasket failures in the 1.4 usually causes oil in the coolant or coolant in the oil. This manifests itself as "chocolate milkshake" on the dipstick, oil filler cap, or in the coolant expansion tank.
There is a black baffle in the bottom of the expansion tank and a small build up of "crud" is not unusual. If he thought it was oil, oil is lighter than water (coolant) and will float to the top.

I thought that maybe the sensor that opens the fan on full speed (I think blue) is working correctly but the green one (temp management sensor) is broken, but that is only my speculation. 

The radiator fan is run by the engine ECU. The engine ECU gets it's engine temp from the green sensor.

I'm a little concerned here. On one hand you have all the earmarks of a failing sensor, but on the other you have had an actual boil over event!
First up, I would make sure the radiator fan actually works...and works as advertised! If you have air conditioning, turning it on should cause the the fan to run. Maybe fast, maybe slow...but it should run.
If you don't have A/C, idling the engine, from cold, the fan should come on at least once within 15-30 minutes. And the temp should remain at 3 bars.
Another test is to idle the car and remove the electrical connector from the GREEN temp sensor on the thermostat housing. Within 20 seconds the fan should run at FULL speed.

DO YOU HAVE AUTO AIR CONDITIONING? Failure of the radiator fan will bring on all the temp lights but the fan will not run! I have personally been caught out by this one! Initially it looks like a harmless sensor fault. No over heating in the engine bay, no nothing. So you ignore it ("I'll get to it later"). But after half an hour in stop start traffic...steam from under the bonnet! Here my knowledge (or my fat head) worked against me.

Tried opening a/c, the fan didn't turn on neither on full or low a/c setting and neither on cold or hot setting.
Removed the temp sensor and within 5 seconds the temperature got to the top, started beeping and the fan opened at full speed and even stayed on after turning the car off.
Sensor still displays nonsense after connecting it back (started at 0, next second got to 2 immediately).

Seems like I will switch the sensor to begin with and then see if the car fan works, if not I will also change the car fan and even if that doesn't work I will see if there is a blown head gasket.

[PaulC5]

The air con not getting cold could be it needs to be regassed with refrigerant.

[ozvtr]

Tried opening a/c, the fan didn't turn on neither on full or low a/c setting and neither on cold or hot setting.
Removed the temp sensor and within 5 seconds the temperature got to the top, started beeping and the fan opened at full speed and even stayed on after turning the car off.
Sensor still displays nonsense after connecting it back (started at 0, next second got to 2 immediately).

Seems like I will switch the sensor to begin with and then see if the car fan works, if not I will also change the car fan and even if that doesn't work I will see if there is a blown head gasket.

No, no. That proves the fan is working correctly! Also, if the A/C is not working the fan wont come on. I was concerned that there was a fault in the fan circuit causing your problems, but it is not. Don't replace the fan.

If you read the other post, that PaulC5 linked to, there is a blue sensor under the thermostat housing on the cylinder head (for a 2002 model). You will need to remove the air filter box to get to it.
The next thing I would do is remove the electrical connector from this sensor and put the air filter box back. Then drive the car normally.
I wont go into what this sensor does but the sensor is unimportant. However it is known to cause this problem.
If the problem comes back, then replace the green sensor, that's your problem.
If your problem goes away after disconnecting the blue sensor, don't bother replacing the sensor and leave it disconnected. As I said, it is unimportant.

So your next step is to find and disconnect the blue sensor. Sorry that this is so protracted.

As a Post Script. In 2005 they did away with this blue sensor.

[kyrpousin]

Tried opening a/c, the fan didn't turn on neither on full or low a/c setting and neither on cold or hot setting.
Removed the temp sensor and within 5 seconds the temperature got to the top, started beeping and the fan opened at full speed and even stayed on after turning the car off.
Sensor still displays nonsense after connecting it back (started at 0, next second got to 2 immediately).

Seems like I will switch the sensor to begin with and then see if the car fan works, if not I will also change the car fan and even if that doesn't work I will see if there is a blown head gasket.

No, no. That proves the fan is working correctly! Also, if the A/C is not working the fan wont come on. I was concerned that there was a fault in the fan circuit causing your problems, but it is not. Don't replace the fan.

If you read the other post, that PaulC5 linked to, there is a blue sensor under the thermostat housing on the cylinder head (for a 2002 model). You will need to remove the air filter box to get to it.
The next thing I would do is remove the electrical connector from this sensor and put the air filter box back. Then drive the car normally.
I wont go into what this sensor does but the sensor is unimportant. However it is known to cause this problem.
If the problem comes back, then replace the green sensor, that's your problem.
If your problem goes away after disconnecting the blue sensor, don't bother replacing the sensor and leave it disconnected. As I said, it is unimportant.

So your next step is to find and disconnect the blue sensor. Sorry that this is so protracted.

As a Post Script. In 2005 they did away with this blue sensor.

The a/c opens normally (pushes air) it just doesn't work as good as it used to in the cold setting.

But couldn't it be that the fan doesn't work at low speeds (example when opening the a/c) and only opens at high ones?
The mechanics said that it sometimes opens and sometimes does not. But as you said the fan is working in general.
Isn't the fan being technically controlled by the green sensor?
So why is the fan not opening in time? Because of the sensor? Or because of some relay?

Also if I did understand correctly the blue sensor only works when the car goes in high temperatures.
My car temperature is constantly changing (from 0 immediately to 2 without passing from 1, from 3 immediately to 5 without passing from 4) so I thought it would be the green sensor that has the problem.

Sorry if I have any mistaken thoughts, correct me if needed.

[PaulC5]

Are you getting confused with the cabin blower and the engine fan, you seem to have 2 separate problems from what I have read ?
Problem 1, a coolant high temperature warning.
Problem 2 the air con is not blowing as cold as it used to. In good order with enough refrigerant it should be able to drop the temperature by 10 to 15°C through the central air vents. It probably just needs regassing.

The blue sensor is working all the time but only switches the high temperature warning on if the coolant temperature is high or at a low temperature if it is faulty. As ozvtr has said, simply unplug it and see what happens.

[kyrpousin]

Are you getting confused with the cabin blower and the engine fan, you seem to have 2 separate problems from what I have read ?
Problem 1, a coolant high temperature warning.
Problem 2 the air con is not blowing as cold as it used to. In good order with enough refrigerant it should be able to drop the temperature by 10 to 15°C through the central air vents. It probably just needs regassing.

The blue sensor is working all the time but only switches the high temperature warning on if the coolant temperature is high or at a low temperature if it is faulty. As ozvtr has said, simply unplug it and see what happens.

My main problem isn't that the a/c doesn't work as good as it used to, I just said that incase it has something to do with the broken car fan.

Now I understand that the a/c is a separate problem and I don't really care about that.
I will disconnect the blue sensor and see what happens, thanks.

[ozvtr]

But couldn't it be that the fan doesn't work at low speeds (example when opening the a/c) and only opens at high ones?
The mechanics said that it sometimes opens and sometimes does not. But as you said the fan is working in general.

I believe the fan is working. Some cars only have a single speed fan. HOWEVER I do not know what YOUR car is supposed to have. Do not worry about it for the moment, we need to sort out the temp gauge problem first.

Isn't the fan being technically controlled by the green sensor?

NO. As I said, it's controlled by the engine ECU. The A/C system can also "request" the engine ECU turn the fan on. The engine ECU takes in information from sensors and other systems on the car and decides if the fan should be turned on. So it's not just the green sensor that controls the fan.

So why is the fan not opening in time? Because of the sensor? Or because of some relay?

AGAIN, IT'S IMPORTANT, DO YOU HAVE AUTO AIR CONDITIONING!!!!! Does the the A/C panel consist of buttons and a display? These cars have a VERY DIFFERENT radiator fan...and it's known to fail! I have personally been caught out by this one!!! MY car boiled over from the fan failing and it caused the same symptoms and it fooled me! DO YOU HAVE AUTO A/C?! If you do not then it's unlikely to be the fan.

Also if I did understand correctly the blue sensor only works when the car goes in high temperatures.

I didn't want to "muddy the waters" by going into the blue sensor, but here is what it does. It monitors the ACTUAL cylinder head temperature. NOT THE ENGINE COOLANT! It has nothing at all to do with the engine coolant. When the CYLINDER HEAD temperature gets to 120'C it sets this sensor off. It will cause all the temp lights to come on and cause the radiator fan to come on. So you can see that if it goes faulty, it can cause the symptoms you are experiencing.

My car temperature is constantly changing (from 0 immediately to 2 without passing from 1, from 3 immediately to 5 without passing from 4) so I thought it would be the green sensor that has the problem.

OK. First up, it is very common (if not the norm) for the temp display to go from nothing to 2 bars. It then can take awhile to reach 3 bars, again, not uncommon. In winter it may take a long time to get to the 3rd bar! However once the 3rd bar is reached, the temperature should remain there and not fluctuate.
With all due respect I believe you mean the display jumps up to the 6th bar. There are 4 lights that are yellow, 1 orange light and the 6th light is red.
If the display "jumps" from 3 bars to 6 bars, that indicates a system failure and not an over heat condition. Particularly if you open the bonnet and there are no signs of an over heat condition. An over heat condition does not happen instantly. The temperature will creep up.

DO YOU HAVE AUTO A/C?

[ozvtr]

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.
It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 

This is concerning. It indicates an actual over heat condition. This should not happen if the radiator fan is working. But you tested it and it worked. If the problem is "just a sensor failure" the fan automatically comes on as a fail-safe. So a boil over should not occur.

If you have auto A/C, it has an electronic fan speed controller built into the radiator fan. If they fail they can exhibit the same symptoms as you are experiencing, lights and all. AND they can become intermittent. Meaning that after they fail, they can start working again! HOWEVER, they are VERY expensive to buy. So I don't want you spending money unnecessarily.
The reason I'm so frantic about this is that you could have another boil over event if the problem is the fan. That's not good for the engine!

I am kicking myself because I have JUST experienced this! But I couldn't believe someone else would have the same problem so soon.

I need to know if you have auto A/C.

[kyrpousin]

Fast forward to one month ago, after a 1 and a half hour trip we stopped in my house to get our baggage out and left the car running so it cools down after the trip (for around 5 minutes). Then when my dad started to reverse and leave I heard a big splash, I come out of the house and see smoke everywhere.
It was all the coolant that splashed, next day the mechanic says that the radiator blew up, we change the radiator and the car runs fine since then but obviously the temperature indication problem still persists. 

This is concerning. It indicates an actual over heat condition. This should not happen if the radiator fan is working. But you tested it and it worked. If the problem is "just a sensor failure" the fan automatically comes on as a fail-safe. So a boil over should not occur.

If you have auto A/C, it has an electronic fan speed controller built into the radiator fan. If they fail they can exhibit the same symptoms as you are experiencing, lights and all. AND they can become intermittent. Meaning that after they fail, they can start working again! HOWEVER, they are VERY expensive to buy. So I don't want you spending money unnecessarily.
The reason I'm so frantic about this is that you could have another boil over event if the problem is the fan. That's not good for the engine!

I am kicking myself because I have JUST experienced this! But I couldn't believe someone else would have the same problem so soon.

I need to know if you have auto A/C.

Yes, I have auto a/c

[kyrpousin]

But couldn't it be that the fan doesn't work at low speeds (example when opening the a/c) and only opens at high ones?
The mechanics said that it sometimes opens and sometimes does not. But as you said the fan is working in general.

I believe the fan is working. Some cars only have a single speed fan. HOWEVER I do not know what YOUR car is supposed to have. Do not worry about it for the moment, we need to sort out the temp gauge problem first.

Isn't the fan being technically controlled by the green sensor?

NO. As I said, it's controlled by the engine ECU. The A/C system can also "request" the engine ECU turn the fan on. The engine ECU takes in information from sensors and other systems on the car and decides if the fan should be turned on. So it's not just the green sensor that controls the fan.

So why is the fan not opening in time? Because of the sensor? Or because of some relay?

AGAIN, IT'S IMPORTANT, DO YOU HAVE AUTO AIR CONDITIONING!!!!! Does the the A/C panel consist of buttons and a display? These cars have a VERY DIFFERENT radiator fan...and it's known to fail! I have personally been caught out by this one!!! MY car boiled over from the fan failing and it caused the same symptoms and it fooled me! DO YOU HAVE AUTO A/C?! If you do not then it's unlikely to be the fan.

Also if I did understand correctly the blue sensor only works when the car goes in high temperatures.

I didn't want to "muddy the waters" by going into the blue sensor, but here is what it does. It monitors the ACTUAL cylinder head temperature. NOT THE ENGINE COOLANT! It has nothing at all to do with the engine coolant. When the CYLINDER HEAD temperature gets to 120'C it sets this sensor off. It will cause all the temp lights to come on and cause the radiator fan to come on. So you can see that if it goes faulty, it can cause the symptoms you are experiencing.

My car temperature is constantly changing (from 0 immediately to 2 without passing from 1, from 3 immediately to 5 without passing from 4) so I thought it would be the green sensor that has the problem.

OK. First up, it is very common (if not the norm) for the temp display to go from nothing to 2 bars. It then can take awhile to reach 3 bars, again, not uncommon. In winter it may take a long time to get to the 3rd bar! However once the 3rd bar is reached, the temperature should remain there and not fluctuate.
With all due respect I believe you mean the display jumps up to the 6th bar. There are 4 lights that are yellow, 1 orange light and the 6th light is red.
If the display "jumps" from 3 bars to 6 bars, that indicates a system failure and not an over heat condition. Particularly if you open the bonnet and there are no signs of an over heat condition. An over heat condition does not happen instantly. The temperature will creep up.

DO YOU HAVE AUTO A/C?

I might be wrong about the number of temp lights but it jumps from the 3 light (yellow) to the top (red) without passing through the orange first.
Let's say it is in the third light and all of the sudden in a red light it goes to the top and the car fan opens at full speed for 2 minutes, then the temperature goes back to 3, fan turns off and everything is normal again.

Again yes I have auto a/c, I sent how my a/c controller looks in the picture for reference.

[ozvtr]

Yes, I have auto a/c

Ok, in that case I'm now very suspicious of the radiator fan.
As I said, the fan has a built-in electronic controller that will vary the fan speed from off to full speed. The built-in controller also provides feed back to the engine ECU about the status of the fan. A fault in the fan will cause all the temp lights to come on and issue three warning beeps. Just like a sensor failure.
Only the cars with auto A/C have this type of radiator fan! Which is why I needed to know.
Again, the electronics in these things tend to be intermittent, and so tend to work sometime and then not others. Which is why it passed the test earlier.
But more importantly, it also answers the question as to why the engine boiled over.
To confirm this, the next time all the lights come on, and you hear the three beeps, pull over BUT DO NOT STOP THE ENGINE, open the bonnet and see if the fan is running.
WITH ALL THE TEMP LIGHTS ON THE FAN MUST BE RUNNING (under any circumstance)!!! If not, that's a failure of the fan!
Even with a failure of the green or blue sensors, the fan should still come on!
If the fan is not working with the car at low speeds (or stopped), the engine will boil over! If you manage to keep the car moving, that will cool the radiator, and you have less of a chance of the engine boiling over.