Intermittent elevated temperature readings

[CoralNova]

I possess a 2013 C180 (W204) (1600 petrol) BlueEfficiency estate featuring the AMG sport package.
The temperature indicator periodically reaches the red zone, seemingly when the engine is under strain, albeit not consistently—typically during prolonged inclines or at high speeds above 70 mph.
The "stop engine" alert has occasionally activated.

However, I do not believe the engine is genuinely overheated.
The coolant is transparent, and there are no indications of head gasket issues.
The gauge fluctuates, but as I decelerate, it returns to normal and may operate for hours without issue, remaining within the standard range, provided I do not exert excessive pressure.
The Hi Tech Performance Garage conducted a comprehensive inspection and identified no concerns; nevertheless, I question if they performed an extensive road test, subjected it to maximum load, or utilised their rolling road.
Do you have any experience with this or any recommendations?

[BeardAndBeans]

Replace the temperature probe? 🤔

[Hypabl]

I encountered the identical issue with my ALFA 156 V6 Veloce 2.5 Busso. It required some time for me to comprehend it. Under typical driving conditions and loads, it functioned adequately; but, at elevated RPMs and loads, when attempting to circulate the water more rapidly, it overheated until I reduced speed, contrary to expectations given the airflow through the radiator at high speeds. The issue was identified as the water pump. The plastic impeller of the water pump was slipping on the shaft under load, obstructing the water flow. Upon replacing the pump, I was able to manipulate the impeller on the shaft using merely firm finger pressure. It appears to be a prevalent problem, as the new ALFA authentic replacement pump had a metal impeller affixed to the shaft by soldering. While it may not apply to your situation, I felt compelled to mention it because of the same symptoms. Have you attempted to bleed it to ascertain the presence of an airlock? Have you disassembled any components of the cooling system recently?

[CoralNova]

Thank you; I believed that could serve as an effective beginning point. Worth a try.

[Spiderer]

... not yet.

The temperature gauge should remain stable until it reaches the appropriate temperature; thus, any fluctuations indicate considerable variance.


My initial action would be to substitute the thermostat and purge the radiator. The pump presents a compelling option; perhaps an expert will arrive shortly to verify whether this is a recognised issue with the engine.

[CoralNova]

If you maintain composure when others are losing theirs, you are evidently neglecting the seriousness of the circumstances. Engineering revolves around identifying the most efficient solution. Phil Wang ALFA Romeo: Employing outdated technology to generate future challenges in the present.
I like it, such lovely aphorisms.

I will include "AMG signifies All Money Gone."
As an engineer, I adhere to Ockham's Razor, a problem-solving theory asserting that the simplest explanation with the least number of assumptions is the most like to be accurate. Also referred to as the principle of parsimony, it is utilised for selecting among competing theories. For instance, in the case of a headache, the more straightforward explanation of dehydration is preferred over a more intricate one such as a brain tumour.
Your hypothesis regarding the water pump is rational, and I will not dismiss it.
I don't think it's an airlock problem.
The car is relatively new to me, yet there are no indications of any maintenance performed on the engine or cooling system. The vehicle possesses a complete service history from Mercedes; nonetheless, I will henceforth conduct all maintenance independently.
I have recently acquired an xTool D8 scanner and a Picoscope Oscilloscope for comprehensive testing, however I recognise that these may not reveal any issues because the garage conducted all standard assessments. Nonetheless, I can likely conduct live monitoring during the road test with it.
I have decided to opt for the more economical choice, a new temperature sender, initially; at 80,000 miles, it is likely a prudent preventative measure.
I greatly appreciate your insight.

[NotePapa]

Another inquiry, the response to which will indicate either a well operating cooling system or an instrument malfunction: does your heater emit hot air during this occurrence?

If you are experiencing excessively hot air, it indicates that water is moving through your engine and heater matrix; this suggests a sensor issue.

[CoralNova]

Another concern I encountered with this vehicle, for the benefit of others: Upon acquiring this pre-owned car with 79,000 miles, it exhibited a knocking sound in the back when traversing potholes.

The local garage and I could not identify any issues. Their health assessment revealed no indications of bush or joint wear, yet a clunking sound persisted.
Ultimately identified the issue through a process of elimination as the rear shock absorbers.
No evidence of leaks; nonetheless, internal complications were present.
I replaced the rear shocks with new Bilstein units, which were half the price of genuine Mercedes parts, and the vehicle now operates flawlessly.

[CoralNova]

Thank you, that is a valid observation. The heater appears to be functioning normally. Completed an extensive motorway trip, and the heater did not exceed the normal temperature. I perceive that the engine is not overheating; nonetheless, this is merely a perception without substantiation.
Thank you for the valuable suggestion.
"Every seat is first class" - I concur with your assessment; I am new to this vehicle and appreciate its driving experience.
 

[CoralNova]

Indeed, I am concerned that if this is a genuine overheating problem, it may cause damage.
It is peculiar that the vehicle can operate for weeks without issues during regular driving around home, then occasionally the gauge rises unexpectedly.
This has occurred while ascending a lengthy hill, though not consistently on this route.

Yesterday, accelerating on the motorway triggered the issue, but when I reduced speed to 60 mph, the gauge returned to a normal and stable reading for 30 miles—no additional complications—until I increased speed back to 70 mph.
Thank you very much

[CoralNova]

Is there a single temperature sensor or multiple sensors on the C180 fuel model?
Is it located in an accessible area? This is my initial step; I will substitute the sensor(s) with authentic Mercedes components.

[CoralNova]

https://www.ebay.co.uk/sch/i.html?_nkw=mercedes parts&campid=5338181132&customid=2518X1570512Xc5dd3e351f4bfbf7a5e310dea288df6d&mkcid=1&mkrid=710-53481-19255-0&subId2=15&toolid=10001