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Old February 25th, 2018, 21:20   #1
halfbytecode
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Default Diagnose thermostat/temp sensor issues, when no errors show up

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.
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Old February 25th, 2018, 21:26   #2
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.
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Old February 25th, 2018, 22:25   #3
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Quote:
Originally Posted by UhOh View Post
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?

Last edited by halfbytecode; February 25th, 2018 at 23:27.
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Old February 26th, 2018, 09:16   #4
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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 . . .
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Old February 26th, 2018, 16:36   #5
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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.
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Old February 26th, 2018, 17:09   #6
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Quote:
Originally Posted by UhOh View Post
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.
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Old February 26th, 2018, 20:16   #7
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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 40F to 70F, in the "extreme" winters. During summers, it goes up to the range of 80F to 120F.

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.

Last edited by halfbytecode; February 26th, 2018 at 20:22.
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Old February 26th, 2018, 20:51   #8
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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.
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Old February 27th, 2018, 00:16   #9
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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.

Last edited by Henrick; February 27th, 2018 at 00:28.
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Old February 27th, 2018, 02:18   #10
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?
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Old February 27th, 2018, 04:32   #11
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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/tem...ant_sensor.pdf
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Old February 27th, 2018, 09:18   #12
halfbytecode
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Quote:
Originally Posted by meerschm View Post
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/tem...ant_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 97C.

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?
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Old February 27th, 2018, 13:50   #13
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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.
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Old February 27th, 2018, 14:33   #14
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Most cars will have a sensor in the radiator in addition to one in AC relay.
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Old February 28th, 2018, 01:15   #15
Henrick
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Quote:
Originally Posted by halfbytecode View Post
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

Last edited by Henrick; February 28th, 2018 at 01:22.
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