7 hours ago, Skodaudi said:

👆

Well, I went over to a mechanic friend of mine today. It is certain that the thermostat is not open, it is certain that the engine would heat up as it should, but for some reason it cannot. It was specifically read with a VW group OBD reader. The inlet coolant temperature is 45 degrees Celsius, the outlet coolant temperature is 5 degrees Celsius. The car had already traveled 30 km. His tip is that there might be something with the auxiliary pump. My car was a police car and it has a Webasto heater. The cooling water is also circulated in this system. Could these be related? I am attaching some pictures of this Webasto.

UPDATE! 
This morning, after driving about 5 km, the water temperature started to rise and did not drop. It stopped at 90 degrees and stayed that way, neither going up nor down. The outside temperature is between -6 and -8 degrees. After I arrived at work, I opened the hood. The fan was spinning at maximum. I was able to touch the pipes again without any problems, but I don't know how hot it should be now. I plugged in the older OBD reader I had and it again read the water temperature around 50 degrees. I don't know exactly where it read this temperature from then. The car had a transmission repair not long ago. Before that, it threw the START-STOP ERROR, but after the transmission was replaced, it was fixed and working. This morning, it threw this error again. I thought it had something to do with the transmission, but it's suspicious that these two things happened at the same time. Now I really don't understand what's happening... 🤣

Certainly interesting. I believe that the temperature that is shown with the gauge is read from the cylinder head. If your tool reads the outlet from the radiator it would make sense in this case. However it would not make sense with the earlier readings if the thermostat was closed.

 

What year the car it is? Do you happen to know what ea211 variant it is (model code)?

 

I believe you have another coolant circulation for the charge air cooler + exhaust around turbo. This circuit has its own electrical coolant pump that should run on demand. Theoretically if it runs all the time it would cause excessive cooling, but I think it is isolated from the main coolant circulation so should not cause your problems. But i guess it could be possible if the isolation is also failed. You friends VCDS/ODIS whatever VAG tool could be used to see if the pump is running even when the car is cold.

 

Since you mentioned transmission, some engines have separate thermostat or valve for gear box cooling but I think it is only for more powerfull engines and not the case with 1.4 tsi. Failure of these 'dsg thermostats' cause some temperature problems but not as dramatic as yours.

 

The webasto. Well it should not cause cooling but theoretically if there is multiple problems with it, it could be cooling the coolant to some extent but i dont believe it. The unlikely scenario would be that it runs automatically everytime you start driving and the system works even tho there is no flame in webasto (should not work then), meaning the webasto water pump runs and the combustion air blower blows cold air into the combustion chamber, making it basically a cooler instead of heater. However now that I think it, it would not have enough cooling power to cause your problem even in this case...

 

Well okay your webasto is installed by a third party so in case it is installed somehow wrong (wrong pipes or something) then maybe it could related. Have you used the webasto? Does it work? 

 

I still see most likely reason to be one of the two thermostats being faulty somehow. Or the charge air cooling circuit running all the time and being connected to main circuit.

28 minutes ago, Skodaudi said:

Certainly interesting. I believe that the temperature that is shown with the gauge is read from the cylinder head. If your tool reads the outlet from the radiator it would make sense in this case. However it would not make sense with the earlier readings if the thermostat was closed.

 

What year the car it is? Do you happen to know what ea211 variant it is (model code)?

 

I believe you have another coolant circulation for the charge air cooler + exhaust around turbo. This circuit has its own electrical coolant pump that should run on demand. Theoretically if it runs all the time it would cause excessive cooling, but I think it is isolated from the main coolant circulation so should not cause your problems. But i guess it could be possible if the isolation is also failed. You friends VCDS/ODIS whatever VAG tool could be used to see if the pump is running even when the car is cold.

 

Since you mentioned transmission, some engines have separate thermostat or valve for gear box cooling but I think it is only for more powerfull engines and not the case with 1.4 tsi. Failure of these 'dsg thermostats' cause some temperature problems but not as dramatic as yours.

 

The webasto. Well it should not cause cooling but theoretically if there is multiple problems with it, it could be cooling the coolant to some extent but i dont believe it. The unlikely scenario would be that it runs automatically everytime you start driving and the system works even tho there is no flame in webasto (should not work then), meaning the webasto water pump runs and the combustion air blower blows cold air into the combustion chamber, making it basically a cooler instead of heater. However now that I think it, it would not have enough cooling power to cause your problem even in this case...

 

Well okay your webasto is installed by a third party so in case it is installed somehow wrong (wrong pipes or something) then maybe it could related. Have you used the webasto? Does it work? 

 

I still see most likely reason to be one of the two thermostats being faulty somehow. Or the charge air cooling circuit running all the time and being connected to main circuit.

The exact engine type is EA211 CHPA.
 

This Webasto heater was probably installed by a 3rd party. It has a monochrome display. I tried to adjust it, but it didn't do anything, there was no sound. I'm trying to disconnect it from the system because I don't need it. 
I think this could be a Webasto problem, because the engine has just started to cool down better now that it's been so minus degrees outside, so that's a good tip.

I don't know about this charge air cooling circuit, but I'll look into it. The only strange thing is how the dashboard showed 90 degrees? For weeks it didn't even go above 50 degrees, even though it wasn't -8 degrees, but plus 5-10.
Let's say when the temperature outside was 10 degrees Celsius, the water temperature only dropped to 70-80 degrees.

 

Anyway, first, I'll try disconnecting the entire Webasto system to see if that's the problem.

SSP511 abut the EA211 engine might be interesting/helpful?, especially page 36 about the cooling system?

Edited 20 February, 20251 yr by PetrolDave

1 hour ago, charsstone said:

The exact engine type is EA211 CHPA.
 

This Webasto heater was probably installed by a 3rd party. It has a monochrome display. I tried to adjust it, but it didn't do anything, there was no sound. I'm trying to disconnect it from the system because I don't need it. 
I think this could be a Webasto problem, because the engine has just started to cool down better now that it's been so minus degrees outside, so that's a good tip.

I don't know about this charge air cooling circuit, but I'll look into it. The only strange thing is how the dashboard showed 90 degrees? For weeks it didn't even go above 50 degrees, even though it wasn't -8 degrees, but plus 5-10.
Let's say when the temperature outside was 10 degrees Celsius, the water temperature only dropped to 70-80 degrees.

 

Anyway, first, I'll try disconnecting the entire Webasto system to see if that's the problem.

 

Might be possible that cold enough weather has not triggered the charge air circuit pump and thus it is not cooling now. Yet I feel the cause is more likely one of the two thermostats at the water pump. But I follow with interest what the outcome will be. Surely this will get sorted out eventually

 

I will also be very surprised if the webasto system is the cause. If installed correctly I can not believe it would cool the engine so much even by the very unlikely theory I presented. How you plan to disconnect it? Unplug power to its pump and blower? That should disable the possibility of it causing the cooling. Total removal includes water and fuel lines etc.

 

Edit. And yeah you dont have gear oil cooler. And only two coolant temperature sensors, one at cylinder head (G62) and one at radiator outlet (G83). 

Edited 20 February, 20251 yr by Skodaudi

If the charge air circuit pump remains as a suspect, perhaps some circut diagrams could reveal what possible sensor may trigger it to run (outside temp, intake air temp, etc.) and then I would try to see if any of those temperature sensor give unplausible readings (a proper scan tool would be needed).

 

Or as more straight forward option perhaps just check all temperature sender readings anyway if you get a change to use such scan tool. 

The picture of how the cooling system works is starting to come together, but it also produced this morning phenomenon on the way home. When starting up again, the cooling fan was running at maximum speed, but after about 5 minutes of city use, the water temperature indicator on the dashboard showed 90 degrees. After 15 km, the water temperature indicator suddenly dropped to 50 and the fan also turned off. What can cause this now? Yesterday, when we removed the G83 sensor with the engine running, the fan was still spinning at full speed. Could there be a connection between this or has something gone wrong in your brain?

3 hours ago, charsstone said:

The picture of how the cooling system works is starting to come together, but it also produced this morning phenomenon on the way home. When starting up again, the cooling fan was running at maximum speed, but after about 5 minutes of city use, the water temperature indicator on the dashboard showed 90 degrees. After 15 km, the water temperature indicator suddenly dropped to 50 and the fan also turned off. What can cause this now? Yesterday, when we removed the G83 sensor with the engine running, the fan was still spinning at full speed. Could there be a connection between this or has something gone wrong in your brain?

Weird if the fan spins right after start-up. I take it the car was cold?

 

Sudden drop feels like G62 gives faulty readings? Or perhaps the charge air cooler pump turned on. Or thermostat opening and staying open.

 

When you disconnect G83 ecu might have to assume that coolant needs cooling and spins the fan just to be sure the car does not overheat. Have you tried disconnecting G62?

Edited 20 February, 20251 yr by Skodaudi

11 hours ago, Skodaudi said:

Weird if the fan spins right after start-up. I take it the car was cold?

 

Sudden drop feels like G62 gives faulty readings? Or perhaps the charge air cooler pump turned on. Or thermostat opening and staying open.

 

When you disconnect G83 ecu might have to assume that coolant needs cooling and spins the fan just to be sure the car does not overheat. Have you tried disconnecting G62?

Yes, it did spin the cooling fan on cold starts. It didn't do it this morning. 

 

Unfortunately, the mechanic friend I know who has the official VCDS software is unavailable, so I won't be able to read what signals the temperature sensors are sending. Car mechanics have been really busy lately, at least here in the area. They can only give me an appointment after 2-3 weeks. 

 

I'll try to replace these sensors, if it's not a nuclear physics thing, and see if it helps.

I haven't disconnected the G62 yet. What will happen? 

 

So I understand correctly that the charge air cooling pump shouldn't run on cold starts? Because, as we looked, the charge air cooling pump didn't run on cold starts. But I think you can also find out this with a software readout...or can you hear when the charge air cooling pump starts?

UPDATE!
G83 replaced. No change.

Question. Can this area cause overcooling?

 

 

16 minutes ago, charsstone said:

Question. Can this area cause overcooling?

 

 

I would not think that to be likely.

On 21/02/2025 at 04:50, charsstone said:

After 15 km, the water temperature indicator suddenly dropped to 50

How quickly did it drop? 1 second, 1 min, and did the heater get any cooler? Eg did the engine actually get cooler.

 

Can you unplug the charge air coolant pump and see if it changes the results.

 

I would think it could potentially cause excessive cooling...but not sure how much the effect on the engine temp would be as the thermostat should control the engine temp still.

 

!!!UPDATE!!!

Well, I set aside the weekend again and set about inspecting/repairing it. The thermostat was removed again. It is closed by default, it opens in boiling water. There is no problem with it. G83 sensor replaced. We had difficulty accessing the G62 sensor. We did not replace it. We sprayed the connector with contact spray. We disconnected the auxiliary heater pipe and unplugged it. No change. Maybe the water temperature indicator on the dashboard does not even show 55 degrees anymore. It blows hot air into the passenger compartment, water does not run out, the pipes leading to the cooling system do not heat up after starting. Now I have to leave this to a specialist and take it to someone who knows about TSI engines. My competence has expanded so far. I got an appointment for March 19th. 
Thank you very much for the help so far! ❤️ It was a good decision for me to join the group. 😊
If anyone has any more ideas or questions, I'd be happy to answer them.
If the source of the error is found, I'll definitely write it down here!

To save me reading back through all the postings, have you ever actually measured the coolant temperature after driving several miles with either an old school mercury bulb thermometer or an infra-red one?

 

All I have read is assumptions that it must be overcooling because of what the dashboard temperature gauge or diagnostic tool says it is not what the actual temperature is.

!!!UPDATE!!! PROBLEM SOLVED!!!
 

Hello. Sorry for being away for so long, but I had a lot of work to do, plus personal matters, but I won't go into detail about that. 
The point is that the problem is solved. One weekend I tried to replace the G62 water temperature sensor. It was quite tricky. You couldn't see anything, since this sensor is behind the engine, so I did it by feel. That was the problem. I don't know exactly how the old one broke, but replacing solved it. So the engine was heating up all the time, but it didn't sense it. If this had been the first thing I replaced, I would have saved 100 euros for sure. 😅
Thank you all for your help! I finally managed to solve it because of you. 😊