No coolant discharge when changing lower temperature sensor

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My Name: bread

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Posts: 2
Joined: Fri May 29, 2020 4:26 pm
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 i
Fuel Type: Petrol
Mileage: 80000
Trim Level: VTR+
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)

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I recently changed both the upper and lower temperature sensors on my 2003 C3 1.4i because I was having issues with short-term overheating. However, when I removed the lower sensor (blue, single pole), there was no coolant flow from the sensor hole, even with the filler cap off. Is this normal? I opened both bleed screws and there was good coolant flow, so there doesn't appear to be air in the system. Thank you for your assistance.
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My Name: Arfur Dent

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Model: C3 2002-2005, Original shape model
Year: 2002 (52)
Engine Size: 1.4 (16v)
Fuel Type: Diesel
Mileage: 100000
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: RHD (UK)
Engine name: DV4 16-valve diesel (90 PS)
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bread wrote: Fri May 29, 2020 6:10 pm I recently changed both the upper and lower temperature sensors on my 2003 C3 1.4i because I was having issues with short-term overheating. However, when I removed the lower sensor (blue, single pole), there was no coolant flow from the sensor hole, even with the filler cap off. Is this normal? I opened both bleed screws and there was good coolant flow, so there doesn't appear to be air in the system. Thank you for your assistance.
Hi


The best thing to do when changing cooling parts on such an old car is to fully drain down, flush and refill with fresh coolant.
These maintenance routines are often ignored on older cars and the problems build up.

Inspecting the colour of the expelled coolant can indicate the state of the cooling system.

There are some specific instructions for filling the C3 cooling system for ensuring the air is fully expelled.
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My Name: Ozvtr

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Posts: 936
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
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Hi and welcome to the forum.
bread wrote: Fri May 29, 2020 6:10 pm there was no coolant flow from the sensor hole, even with the filler cap off. Is this normal?
I honestly don't know but all of my research indicates that the blue sensor does not sit in the coolant flow.
The green sensor is used by the engine ECU to monitor the engine coolant outlet temperature. This info is relayed to the dash (if your car has an engine temperature gauge). It is also used by the engine ECU to control various parameters of the engine's operation. It sends out an analog out put signal proportional to the temperature of the coolant.
The blue sensor is the engine over heat sensor. My research indicates it monitors the actual cylinder head temperature (not the coolant) and if it gets over approximately 120'C it triggers an alarm. It is a switch and is either open or closed.

Did you fix your "short term overheating" issues?
My Name: bread

Member
Posts: 2
Joined: Fri May 29, 2020 4:26 pm
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 i
Fuel Type: Petrol
Mileage: 80000
Trim Level: VTR+
Gearbox: Manual 5 speed
DPF: No
LHD or RHD: LHD (Europe)

Post

Ozvtr wrote: Sat May 30, 2020 3:48 am Hi and welcome to the forum.
bread wrote: Fri May 29, 2020 6:10 pm there was no coolant flow from the sensor hole, even with the filler cap off. Is this normal?
I honestly don't know but all of my research indicates that the blue sensor does not sit in the coolant flow.
The green sensor is used by the engine ECU to monitor the engine coolant outlet temperature. This info is relayed to the dash (if your car has an engine temperature gauge). It is also used by the engine ECU to control various parameters of the engine's operation. It sends out an analog out put signal proportional to the temperature of the coolant.
The blue sensor is the engine over heat sensor. My research indicates it monitors the actual cylinder head temperature (not the coolant) and if it gets over approximately 120'C it triggers an alarm. It is a switch and is either open or closed.

Did you fix your "short term overheating" issues?
Your explanation makes sense - thank you! However, the overheat warning still occurs occasionally (but not with aircon running), triggering the fan on high speed (the low speed doesn't seem to kick in in time), and I now have error code P0115 - engine coolant temp sensor 1 circuit. Does this indicate a problem with the replaced green sensor? Thanks again.
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My Name: Ozvtr

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Posts: 936
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
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Things seem to point to the car actually having a cooling problem.
With the aircon on, the fan runs at full speed all the time. I would say this is aiding the cooling of the radiator.
What is your temperature gauge doing during the over heat? Does it indicate normal temperature? Or do the bars indicate a temperature rise?
The temperature sensor is basically an electrical resistor and the engine ECU can tell if there is something wrong with it. However it is highly unlikely a brand new sensor would be faulty. Maybe wiring or the BSM (the engine bay fusebox).
If you idle the engine and pull the electrical connector off the green sensor what happens? After a few seconds the dash should show all the temp bars illuminated and the thermo fan should run flat out.
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