Coolant Temperature Difference: Thermostat vs. Sensor

AFN in G3:
I logged the coolant temperature during the AB test drive.
The outside temperature is 3°C, which is relatively low.
The values from MWB 1 were around 80° during moderate driving, and increased when...
The faster sections reach around 180 km/h, but never exceed 86 °C.
Oil temperature, maximum 96 °.

What was noticeable was that, under low load, the sensor value consistently dropped back to 80° relatively quickly.
It goes down, but then "stops" as if the thermostat is "intervening".
Since the thermostat already kicks in below 87°F, I'm now wondering if...
In the circuit where the thermostat is located, the water simply appears hotter than it actually is.
the temperature sensor.
Could that be possible?

Best regards, Klaus.

Hi,
The temperature sensors are located on the coolant outlet flange (where coolant flows out of the engine), while the thermostat is located on the water pump (where coolant from the small and large circuits is mixed and pumped into the engine block). The coolant coming from the engine is, logically, hotter, so the sensors detect the higher temperature.
Sure, here is the translation of the text from German to English:

"vg" is an abbreviation for "very good". It is often used in online forums and chat rooms to express agreement or approval.
Herbert.

"Same here, especially since the thermostat housing is located at the front, while the sensor is positioned at the rear, in the 'slipstream'."

Okay, thanks. So it seems like the sensor is reporting temperatures that are too low.
The starting value with the engine cooled down was, however, exactly correct.

Best regards, Klaus.

Hm,
I would definitely consider a faulty thermostat as a possible cause.
After the replacement, the coolant temperature (after reaching 87°C) is also within the desired range even during moderate driving, so it's not below 87°C.
/viewtopic.php?t=23345&start=24
haithamina

The thermostat is a thermo-mechanical component.

Firstly, it ages, and secondly, it doesn't switch completely on or completely off within a range of 1°C, but rather over a wider range.

I don't know the exact details, but I could imagine a tolerance range of around +/- 5°C. If you also consider that the coolant sensor and MSG (presumably a temperature sensor) also have a tolerance that is certainly higher than 1°C, then you can reach the range you are experiencing, although I also consider it to be at the limit (but still on the "not yet requiring replacement" side of the limit).

You could also suspect that the thermostat needs replacing and, at home, in a water bath with a suitably accurate thermometer, check its control range. I would be interested in both the control range and the deviation from the target of 87°C .

Greetings.
Sure, here's the translation:

"Guste" is a German word that means "gust" or "gust of wind." It can also be used to describe a sudden burst of something, such as laughter or anger.

Hi!
For me, it's definitely a faulty thermostat; I had the exact same problem.

/viewtopic.php?t=24642&highlight=thermostat

Best regards,