Thermostat: G62, G83 Coolant Temp. Issues

Hello everyone,

I've been experiencing a problem with increased fuel consumption in my Octavia (year of manufacture 2006, 103 kW, non-DPF engine code: BKD) for quite some time now.
Mittlerweile ist schon fast alles ausgetauscht worden, was im Zusammenhang stehen könnte. Without success.
What personally bothers me is the temperature of the coolant.
According to the G62 and G2 measurements, I never exceed 75-80 degrees Celsius during city driving.
I only briefly reach temperatures of 83-85 degrees Celsius during quite steep uphill climbs, but they quickly drop again afterwards.
According to my understanding, the engine control unit (ECU) accesses these values and adjusts the injection parameters accordingly.
"The engine is always running with 'almost warm' values. This means the fuel mixture is too rich, and there's potentially too much fuel?"

I also once read that the MSG compares values between G62 and G83 (i.e., sensors at the cooler outlet) in order to function.
What is your G83 value? For example, if my G62 value is 80 degrees, then my G83 value is around 30-40 degrees.
Is that roughly correct, or should the G83 also have a comparable value?

I'm quite sure that my problem lies in this area, but I don't know if the G62/G2 sensor is faulty, or if the G83 is malfunctioning... it could even be both.
Or whether the thermostat is malfunctioning and unable to provide the required output.
Speaking of thermostats, unfortunately, I couldn't find a thermostat for the BKD engine in the parts catalog.
Does anyone have any idea what it's called and where it's located?

Regards,
Serdar.

Given the current outside temperatures, it's perfectly normal for a TDI engine to not exceed 80 degrees Celsius. Just because the temperature gauge always shows 90 degrees doesn't mean the engine is actually running at that temperature all the time. No engine can maintain such a precise temperature consistently.

It's rather unusual for the G83 sensor to report only about half of what the G62 sensor reports. However, you can try a simple test: Warm up the engine thoroughly, then let it idle (with the heater OFF!!!) for as long as it takes for either the fan to turn on (which might take quite a while with the current outside temperatures) or for the coolant hose to feel roughly the same temperature at its inlet and outlet. If the values from the G62 and G83 sensors are not relatively close then, the G83 sensor is likely defective. As mentioned earlier, the values reported by the G62 sensor are perfectly fine.

I'm not sure exactly where the thermostat is located on a BKD engine. I'm also not very familiar with 2.0 TDI engines. However, it's likely to be at the other end of either the radiator inlet or outlet hose. On 1.9 TDI engines, it's usually at the end of the inlet hose, and it's probably in a similar location on the 2.0 TDI as well. But I can't guarantee that.

That's a valuable answer already, thank you.
The G83 is always located very low. I've accessed it several times in the past few months, and each time it was much lower than the G62. Almost always less than half, or even just a third.
I had also asked about the G83 in a thread before. However, I received the answer that the temperature at the cooler outlet must be low because it is being cooled there .

I had also asked about the G83 in a thread before. However, I received an answer that the temperature at the cooler outlet has to be so low because it is being cooled there .

That's correct. However, that's also why TDI-GTI-4-Motion recommended reading the value while the car is stationary, where the heat exchanger's cooling capacity is minimal (before the fans start), and therefore the temperature at the heat exchanger outlet shouldn't drop significantly.

However, all of this has nothing to do with the issue of increased fuel consumption due to a coolant temperature that is too low. The sensor is not relevant for that. I would suggest replacing the dual-temperature sender as a test and then logging the data. If that doesn't help, then it's likely the thermostat.

Okay, so I always read the values while the engine was stationary. Usually after a few minutes of idling. The G83 value never exceeded 40 degrees; it was mostly between 25 and 30 degrees.
The G62 values are bothering me because they never exceed 85 degrees Celsius. That means I can drive however I want.
Yesterday, for example, I drove through the city non-stop for 3 hours (it's a taxi...I'm not crazy ). The G62 temperature was 82 degrees.

Hi.

So, as we were already discussing, I replaced the G62, G83, and thermostat.
Now the cooling system is warming up quickly and reaching 90 degrees Celsius, even exceeding that temperature. The G62 and G83 have approximately the same temperature – previously, the G83 was always between 20 and 40 degrees.
I don't know how this will affect consumption. I still need to test it.

This is the last thing I'm voluntarily replacing on this car. From now on, no more diagnostics, no more troubleshooting, nothing.
Hopefully, I'll be able to drive this car for a few more months, and then I'll get the new E-Class.
What I've had to endure in recent years due to the incompetence of the VAG workshops is an unbelievable story.
Anyway, around here, they (especially the professionals...) are terrible.

Regards,
Serdar.

Then have a lot of fun with your new Mercedes. So you're basically going from the top to the bottom, from luxury to... well, something else.

Have you had any bad experiences?

I didn't, but my parents did, and many famous people did too.

Here's a quick update:
The temperature sensor G83 at the radiator outlet was functioning correctly. It registered low temperatures when the air conditioning was turned on (which also caused the fan to run).
At Klima Econ, G62 and G83 are almost synchronized. When the climate is activated, the temperature reaches between 30 and 40 degrees.

The G62 and/or the thermostat were not working correctly. Now, the coolant temperature is always 10 degrees higher than it should be. Even if the car has been standing for half an hour, the temperature is still 80 degrees.
Previously, even with the engine fully warmed up, I haven't exceeded the 85-degree mark.

Regarding consumption, however, absolutely nothing has changed. I must have had a logical error there.
I had assumed that the engine control unit (ECU) would incorporate the temperature reading from the G62 sensor into the fuel injection system. It seems that's not the case, though. In any event, the sensor had absolutely no influence on fuel consumption.

Now, I've essentially tried everything, and I'm back to the starting point of my considerations.
Timing belt/timing chain. Even though several mechanics have assured me that it's almost impossible, it could only be related to this. There must be some tolerance range, even for the 2.0 TDI PD engine, even if everyone says: "It either runs, or it doesn't run at all."
I still have 30,000 kilometers to go before the next timing belt replacement, including the tensioner pulley, so I have about 4 months to wait.
Another possible source of the problem could be the turbocharger... but that's less likely. At least, my gut feeling tells me it's not the turbo. After all, it's been running with this issue for 90,000 miles. And in my opinion, if it were the cause, it would have failed long ago.

Here's something else I noticed... maybe someone has an answer to this?
The NOx reduction rate in the measurement data blocks is 245 mg/h (which is as expected).
However, if I go back to the basic settings, I have some confusing data.
With the default settings, it shows a target value (AGR_SOLL) of 7.6 mg/h and an actual value (AGR_IST) of 245 mg/h.
When I set the basic setting, it shows "AGR ON" or "AGR OFF" instead of the target value for the AGR (Active Grille Control).
However, the AGR-IST value is then 190 mg/h when using AGR-AN?
The actuator diagnosis also indicates a value of 190 mg/h for the actual EGR flow rate.
What is actually correct? What's going wrong here?
And generally speaking, how does the basic setup work for a BKD engine?
The label says to press the gas and brake pedals simultaneously to activate the initial setting, but that's not working for me.
I can only set the button to "On." Then it alternately displays "AGR On" / "AGR Off."
I still don't understand what it has to do with a basic setting .

Regards,

PS: I wrote above that I'm not doing anything else to the car... but somehow this topic just won't leave me alone. In any case, I want to clear up the questions in my head... even if it doesn't help me, at least I'll have learned something.

Let's start from the beginning:

What do you mean by "increased consumption"?
I drive my diesel and it consumes between 4.7 and 11 liters – on average.
Nothing is broken; it's just a matter of me, my luggage, and my mood.

Even the difference between 125 and 140 makes a liter of fuel on my 150 km test route.


Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

City driving, approximately 120,000 kilometers driven. Initially, fuel consumption was around 8-8.5 liters, and after the break-in period, it was driven at a maximum of 6.5-8 liters.

"New turbocharger installed at 110,000 km; timing belt replaced at 120,000 km. The car ran well after the new turbocharger, but not after the timing belt replacement. Since then, fuel consumption in city driving has been 9.5-11 liters."
The engine is rumbling, loud, and sounds kind of wheezing. With 4-5 people on board, you can say it's struggling immensely and almost seems like it's about to die.

serdarg wrote:

City driving, approximately 120,000 km in total. Initially, it consumed around 8-8.5 liters, and after the break-in period, it was driven at a maximum of 6.5-8 liters. "New turbocharger installed at 110,000 km; timing belt replaced at 120,000 km. The car ran well after the new turbocharger, but not after the timing belt replacement. Since then, fuel consumption in city driving has been 9.5-11 liters." The engine is rumbling, loud, and sounds kind of wheezing. With 4-5 people on board, you can say that it's absolutely struggling and almost dying.

As I mentioned before, you now know that the thermostat is not the cause of the high consumption.

Okay, in that case, I would definitely check the Zylinderkopf (cylinder head) settings very carefully! And also, like last time, remove the hose from the intake manifold before the EGR valve and shine a light into it to see if it's clogged with deposits from the EGR system.

Okay, I'll look into that. The hose came off recently – and there was absolutely no buildup inside the hose itself. It's not easy to shine a light into the intake manifold; I would have to at least remove the intake pipe and the EGR valve to see anything.
I seem to recall looking inside the exhaust manifold a few months ago when the EGR valve was replaced. I didn't see any deposits in there.

PS: Does anyone have an answer to the question about the basic setting? Pressing both the gas and brake pedals at the same time doesn't initiate the basic setting for me (engine code: BKD)... how should I do it?

Quote:

P.S.: Does anyone have an answer to the question about the basic setting? Pressing the gas and brake pedals at the same time doesn't initiate the basic setting for me (engine code: BKD)... how should I do it?

Enter the reset mode with VCDS! Press gas and brake simultaneously with a BKD engine? See if that changes anything, but I doubt it will.

Best regards, Rainer.

And how do you perform the basic adjustment on the BKD engine? The only thing you can do is press a button in VCDS... then the EGR valve turns on and off at intervals.
Is that not yet a setting then?