Diagnose thermostat/temp sensor issues, when no errors show up

halfbytecode

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1.6 TDI - CR, 2010 Polo Sedan
Hi,

I have a 1.6 TDI common rail, that has over 130,000 kms on it. For quite some time, I have noticed the engine takes increasingly longer to warm up. It takes as long as half hour or more of driving. During this time, the acceleration and fuel efficiency is also lower.

I have had the car scanned using VAS at the dealership a number of times, but no errors pop up.

I am wondering if there is a way to diagnose the issue using VAS/ODIS, and determine if it due to the coolant temperature sensor, thermostat, or something else.

Thanks.
 

UhOh

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If you have access to VCDS you can see what the actual temperature is vs. what the gauge temperature is. If these are matching, more or less, then it's going to be the thermostat. If they're wildly off then the CTS is flaky (though this shouldn't really affect REAL temps, just what the gauge is showing- rarely does the engine management side of the CTS [assuming it's like ones in older cars] fail.
 

halfbytecode

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1.6 TDI - CR, 2010 Polo Sedan
If you have access to VCDS you can see what the actual temperature is vs. what the gauge temperature is. If these are matching, more or less, then it's going to be the thermostat. If they're wildly off then the CTS is flaky (though this shouldn't really affect REAL temps, just what the gauge is showing- rarely does the engine management side of the CTS [assuming it's like ones in older cars] fail.
The coolant temperature sensor is the same as the one used in most of the recent VWs with all sorts of engines. Click the image for ECSTuning page.



The thermostat is contained in this enclosure:



I don't have access to VCDS. I can have it checked at the dealership using VAS.

You may be surprised but my car does not have a temperature gauge. It just displays the outside temperature.

Does VAS allow comparing the actual temperature and the temperature usually reported by the gauge?
 
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tadawson

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If no gauge, what causes you to state it is warming up slower and slower? If that observation is based on heater output alone, then a clogged heater core also becomes a possibility . . .
 

UhOh

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Also, to indicate your location as "Somewhere" is TOTALLY non-helpful, especially when we're talking about heating/cooling issues. Location matters as it gives us an idea on what environment the car is operating in.
 

Ol'Rattler

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Also, to indicate your location as "Somewhere" is TOTALLY non-helpful, especially when we're talking about heating/cooling issues. Location matters as it gives us an idea on what environment the car is operating in.
I totally agree on that point. Perhaps during the account creation process there should be some required fields that need to be a condition for having an account such as:
  • Screen name
  • Password
  • Geographic location that gives a climatic region
  • TDI Make, Model, Generation and year (Or None would be O.K.)
I'm sure our Mods would agree to this. It could be set up so that someones first post is in the introductions section with account approval pending by the Mods. The last part I could go either way on.
 

halfbytecode

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1.6 TDI - CR, 2010 Polo Sedan
For some time now, the engine is very sluggish and makes a lot of noise, at cold starts. There is a decrease in acceleration, and fuel efficiency, which I mentioned. The time for which all this happens, has gradually increased. Sometimes it takes as much as a half hour for everything to be normal. For most of my car ownership, this was not the case no matter what the outside temperature was like.

The climate here ranges from 40°F to 70°F, in the "extreme" winters. During summers, it goes up to the range of 80°F to 120°F.

The reason I do not like to disclose the location is because some people tend to form certain perceptions, based on the location. I can show you an example, if you want. Moreover, the location may not give you an idea of the climate, as we have different climates even in places not far away.
 
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UhOh

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Sorry, but you're dancing around here. General climatic information is NOT sufficient. Not a clue what season you're experiencing (folks in the Southern Hemisphere are 180 degrees out).

My patience has run out. My call. Good luck.
 

Henrick

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Golf VI TDI, 77 kW (CAYC)
OP, does your car indicate Oil temperature in the MFD? Usually that temperature is withing 2-3 degrees of *actual* coolant temperature on these engines. Check that and see.

Another thing you can check. Drive the car for a bit and try to check the return hose from the radiator (on the alternator side). Is it cold or hot? Note that most likely you will need to access that from the bottom of the car (things are really tight there) so probably a good idea to remove the belly pan before this experiment.

And with ODIS you can check the actual temperature. Take a car for a longer drive then try to connect the diagnostics tool as soon as possible. Check the readout of Coolant temperature sensor G62 (sth like that). Should show no less than 85 *C. If it's lower, time for a new thermostat.

BTW, I have exactly same engine with almost identical mileage. My thermostat is weak (plan to replace it at the end of upcoming summer, unfortunately this is very labour intensive) and it never heats up over 82-83 *C

EDIT: have you updated the ECU software for this car ever? Assuming you have access to VAS/ODIS, I'd strongly suggest flashing 9972 to it (later ones are Dieselgate fixes, not worth IMHO). That software revision cures A LOT of problems, such as rough/noisy cold starts, moisture accumulation in charge air cooler, shaking during warm up stage and regen, regens are hotter but shorter, fuel economy inclreases slightly.
 
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halfbytecode

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Thank you for the detailed reply, Henrick.

- My car does not display oil temperature in the MFD either. While checking for the coolant temperature sensor readout, is there a way to distinguish if any anomaly is due to CTS or the thermostat?

I am actually hoping it is just the CTS for me. Like you said, changing the thermostat in these cars is very laborious. I saw everything we have to remove on ELSA, and I hope I don't have to do it.

- Regarding the ECU update. Yes, it was updated once in 2011, when the car was about 2 months old. That update did fix all the cold starts issues completely, that were present back then. Those issues were very minor, as compared to the ones I have mentioned here.

I do not know what software version my ECU is currently at, but I will find that out when I have my car scanned.

- Is it possible to choose a software version to update to, in ODIS, or does it just allow you to update to the latest software version?
 

meerschm

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halfbytecode

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if you like, you can access the wiring to the temperature sensor and measure the resistance.

this sensor changes resistance with the temperature, so if you can measure the temperature, you can check the sensor for the specified resistance value.

http://pics.tdiclub.com/data/500/temp_vs_resistance_vw_coolant_sensor.pdf
Thanks for suggesting that. I will try it out.

By the way, I just remembered that after the coolant change, a temperature readout was checked, with the car idling. The radiator fan turned on when the temperature readout had 97°C.

Considering that is the temperature at which the radiator fan should turn on, does it mean the CTS was reporting the correct temperature, or the radiator fan would just turn on whenever the CTS reports that temperature, irrespective of it being correct?
 

meerschm

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2009 Jetta wagon DSG 08/08 205k buyback 1/8/18; replaced with 2017 Golf Wagon 4mo 1.8l CXBB
one would need more information on the Polo than I have. not sure if your car operates the radiator fan based on the coolant sensor coming out of the head, or if a second sensor in the coolant path near the radiator is provided.
 

Henrick

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Golf VI TDI, 77 kW (CAYC)
Thank you for the detailed reply, Henrick.
- My car does not display oil temperature in the MFD either. While checking for the coolant temperature sensor readout, is there a way to distinguish if any anomaly is due to CTS or the thermostat?
I am actually hoping it is just the CTS for me. Like you said, changing the thermostat in these cars is very laborious. I saw everything we have to remove on ELSA, and I hope I don't have to do it.
- Regarding the ECU update. Yes, it was updated once in 2011, when the car was about 2 months old. That update did fix all the cold starts issues completely, that were present back then. Those issues were very minor, as compared to the ones I have mentioned here.
I do not know what software version my ECU is currently at, but I will find that out when I have my car scanned.
- Is it possible to choose a software version to update to, in ODIS, or does it just allow you to update to the latest software version?
It's very sad that you don't have oil temperature displayed. Then you will need some scan tool to monitor the coolant temperature while in motion as well as stationary.

You say you found the documentation in ELSA on how to replace the thermostat on this engine - could you please share it with me? I will need to do this on my own car so some docs would be useful. I'll send you a PM regarding this.

Unfortunately I don't work with ODIS. But I suspect it offers only the latest update (which is what you don't want). But try asking someone experienced if you can choose particular SW version. If they need a recall code, give them EA32. 9972 software was released in 2015 I think, there are quite a lot of improvements...

PS: This engine doesn't have any coolant temperature sensor in radiator nor an AC relay
 
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AndyBees

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I'm not sure when VW began using the CTS to trigger the Fan Control Module to turn on the fans, but I do know the 2008 EOS Gasser has that setup. Also, the FCM is built into the large fan motor.
 

halfbytecode

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1.6 TDI - CR, 2010 Polo Sedan
• It seems the radiator fan would turn on when the CTS reports a temperature of 97°. Whether it reports it correctly or not, seems like another story.

• I was reading about updating the ECU software using ODIS, and it seems it can be done to versions older than the latest. I just need the .bin to supply to ODIS. There is apparently a flag in ODIS, that disables the software version check. However, before proceeding I have to ascertain the software version installed on my car's ECU, and determine the ECU part number, followed by getting ahold of the software 9972 for it.

• I should have access to an OBD2 scanner in a few days, and I will try to check the coolant temperature at cold starts, the time it takes for the temperature to rise, etc. Should I do that first while the car is idling, followed by going to a long drive after that, or both separately on two different days right at cold starts?
 
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Henrick

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If you have a faulty sensor (or wiring!), you will notice it right away. Usually these sensors crack internally. Maximum value for this sensor is set to 140 *C I think, minimum is -40 *C. Both will trigger fan to come on at highest speed as the car doesn't know the real temperature (safety feature).
 

halfbytecode

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Thanks. By the way, I was taking a look at the service manual, and there seem to be two coolant temperature sensors!

One is labelled -G62- which is what we have been referring to, so far. Apart from that there is another CTS labelled -G83- which is called the radiator outlet CTS.

I looked up the part number for G83, and it is the exact same part as G62, just installed as a secondary unit.

Does this change the way the issue should be diagnosed?
 
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halfbytecode

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While reading through the service manual, I came across a rather interesting piece of information:

Checking 4/2-way valve
with thermostat ⇒ Vehicle
diagnostic, testing
and information system
VAS 5051 „Function
and component selection“.

I am going to have the thermostat checked this way.
 

Henrick

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Yeah, there are two sensors. The G83 (which is located next to alternator) is not very important and its value often can be substituded. But you want your G62 working properly.
 

halfbytecode

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I got access to an OBD2 scan tool. I scanned the car for errors, and, as expected, there were none. I will check the coolant temperature shortly, using this tool.

My car does not seem to have am engine oil temperature sensor. There is no data available for engine oil temperature.

I was able to know the ECU software version, and also the exact ECU part number. The software version is 9971. I will try to have it updated to 9972 using ODIS.
 

Henrick

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That's great. 9971 is very good software. 9972 is improvement of course but luckily you don't have those buggy ones versioned <8000
 

halfbytecode

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That's great. 9971 is very good software. 9972 is improvement of course but luckily you don't have those buggy ones versioned <8000
Yes, I was quite certain that I had good software, as the moment it was installed, all earlier cold start issues due to the earlier software vanished. This was way back in early 2011.

The car had no cold start issues for years following that.

Anyway, I checked the coolant temperature today using the OBD tool, while driving the car in the city.

  • Right upon ignition, the coolant temperature was 22°C, as per the data from OBD tool. The outside temperature indicated on the MFD was 23.5°C.
  • The coolant temperature gradually increased to about 60°C in about 10 minutes.
  • From there on, it took a lot of time for the coolant temperature to increase, especially after about 70°C. It finally reached 90°C in about 35 minutes.
  • The coolant temperature began dropping slightly after reaching about 90°C, by nearly a degree or so. It kept fluctuating around 90°C.

As per the service manual, the thermostat starts to open at 92°C. [Fully open at 107°C, just to throw that in]

Does this help?

I will try the same with the car idling, as well as by going on a long drive.
 
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Henrick

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To me it looks like your thermostat is working properly. It might have 1 degree "loss" due to normal wear/age on it.

Idling is not a good measure to check anything in these engines. I have noticed that the coolant temperature gets higher with engine under load and idle RPMs, e.g. when parking in a lot back and forth
 

halfbytecode

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To me it looks like your thermostat is working properly. It might have 1 degree "loss" due to normal wear/age on it.

Idling is not a good measure to check anything in these engines. I have noticed that the coolant temperature gets higher with engine under load and idle RPMs, e.g. when parking in a lot back and forth
I forgot to mention the service manual has approximate temperatures listed for the thermostat opening and fully open states.

What can be the issue for me, if the thermostat and the CTS seem alright? Is it possible there is significant sludge formation in the engine, engine components starting to wear over time, or something else?

Cleaning the fuel injectors using diesel purge helped somewhat.
 

Henrick

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Is the car with DSG? There is a separate thermostat for the DSG which may be faulty.
 

halfbytecode

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Is the car with DSG? There is a separate thermostat for the DSG which may be faulty.
It has a 5-speed manual transmission. I was thinking about the time it takes for the coolant to reach 90°C, which is over 30 minutes. Does that seem normal?
 
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