Coolant Temp - odd readings - 1.4 petrol 2002

[RussellB]

Hi - looking for some advice.

The problem is the coolant temp gauge stopped giving a reading - it used to stay at 90C with no issue.

A common problem and I've read the existing threads suggesting temp sender and thermostat and checking that fan works with climate etc - thanks for the pointers.

I've only changed the sensor for an after-market one and the reading hasn't changed. Coolant hoses warm to radiator suggesting thermostat working.

I plugged in diagnostics and found the following:

1. I can see two temp readings - I guess one for gauge and one for ECU. They are a degree different at times, but I do get a reading that plateaus at 60C and then rises (test at idle)
2. When the temp on diagnostics reaches 100C the engine fan kicks in to start cooling and shuts off when cooled to around 98C
3. The temp gauge on the dash reads 30C below the value on diagnostics - so at 100C the gauge shows 70C

I think this tells me the sender is giving the right value, the thermostat is working and the cooling fan is working from a value from ECU but the gauge is not showing the right value. If I got no value at all from gauge that could be an earth - all other dials working and fuses all good.

Any ideas where to look next? Any prompts appreciated!! thanks

 

[PlasticMac]

As you say, there are two separate sensors, in a single moulding.
The engine diagnostics show the sensor which is used by the ECU.
The other sensor, relates to the gauge, which is not driven directly by the sensor, the gauge is weighted to display 90 C, anywhere be 85C and 100 C.
Instrument diagnostics can show this sensor.
If both sensors give similar readings, but the gauge is well out, l'd look at the cluster.
Does the gauge stop at zero, when the engine is cold?
Mac.
Edit:, Which OBD scan tool are you using?

 

[Andrew]

::..........

1. I can see two temp readings - I guess one for gauge and one for ECU. They are a degree different at times, but I do get a reading that plateaus at 60C and then rises (test at idle) :........

Good Afternoon Russel,

Yes two readings from G62, your guess is correct. A degree or two different is nothing but normal and I would not be concerned at the plateau. I have seen this many times with my FSI, I surmised the effect at this point is caused by the cabin heater deciding to seriously use the warming coolant rather than ticking over.

Question. Do the two G62 outputs stick roughly together all the way up to 100°C?

Andy

 

[PlasticMac]

I think Instruments Controller (17), Group 050 is the one you want, to check cluster temp sensor.
Group 050,0,General
Block 01,Odometer
Block 02,Engine Speed
Block 03,Oil Temperature
Block 04,Coolant,Temperature
Mac.

 

[Andrew]

I think Instruments Controller (17), Group 050 is the one you want, to check cluster temp sensor.
Group 050,0,General
Block 01,Odometer
Block 02,Engine Speed
Block 03,Oil Temperature
Block 04,Coolant,Temperature
Mac.

Good Afternoon Mac,

I don't know about Group 050, I used Group 003.

Andy

 

[RussellB]

As you say, there are two separate sensors, in a single moulding.
The engine diagnostics show the sensor which is used by the ECU.
The other sensor, relates to the gauge, which is not driven directly by the sensor, the gauge is weighted to display 90 C, anywhere be 85C and 100 C.
Instrument diagnostics can show this sensor.
If both sensors give similar readings, but the gauge is well out, l'd look at the cluster.
Does the gauge stop at zero, when the engine is cold?
Mac.
Edit:, Which OBD scan tool are you using?

Thanks Mac. Yes, gauge stops at zero. I'm using iCARSOFT CR MAX diagnostics

 

[RussellB]

Good Afternoon Russel,

Yes two readings from G62, your guess is correct. A degree or two different is nothing but normal and I would not be concerned at the plateau. I have seen this many times with my FSI, I surmised the effect at this point is caused by the cabin heater deciding to seriously use the warming coolant rather than ticking over.

Question. Do the two G62 outputs stick roughly together all the way up to 100°C?

Andy

Thanks Andy - yes, two readings stay together

 

[PlasticMac]

Good Afternoon Mac,

I don't know about Group 050, I used Group 003.

View attachment 118095

Andy

Same data in both.
Group 050 possibly more useful, as includes Engine Speed and Oil Temperature too.
Group 050:
050,0,General
050,1,Odometer
050,2,Engine Speed
050,3,Oil Temperature
050,4,Coolant,Temperature
Group 050 would be idea to log, for a general health check.

Group 003:
003,0,General
003,1,Coolant,Temperature
003,2,Standing Time
003,3,Dimming,(Terminal 58d)
003,4,Dimming,(Terminal 58s)
Mac.

 

[PlasticMac]

Thanks Andy - yes, two readings stay together

Looks like a suspect temperature gauge motor imo.
Any chance of borrowing a cluster to swop, and compare?
I think @timmus can repair a cluster.
Mac.
Edit: There's a company in Dorset, near Wareham Station, Totaltronics, who repair clusters. Did my TT cluster a couple of years ago. If you make an appointment, Patryk can, usually, provide a while you wait service.
Mac.

 

[timmus]

I think @timmus can repair a cluster.

With so many miles separating me from the car, it’s difficult for me to confirm that the cluster is at fault. However, if posted to me, I can indeed test the cluster and enact a repair if required.

Cheers,

Tom

 

[RussellB]

Looks like a suspect temperature gauge motor imo.
Any chance of borrowing a cluster to swop, and compare?
I think @timmus can repair a cluster.
Mac.
Edit: There's a company in Dorset, near Wareham Station, Totaltronics, who repair clusters. Did my TT cluster a couple of years ago. If you make an appointment, Patryk can, usually, provide a while you wait service.
Mac.

Thanks Mac - Wareham's not that far for me so I've booked in with Patryk next week - will update the thread in due course - thanks for your help!