The E250 W212 with the OM651 engine is experiencing a high radiator fan speed and low fuel efficiency, but no error codes are being detected.

[ElectricEclipse]

The vehicle I own is a 2015 E250 CDI estate, equipped with an OM651 engine. The automobile has travelled a total of 118,000 miles without any faults, with 50,000 of those miles driven by me. Recently, my daily commute has consistently achieved a fuel efficiency of 54 miles per gallon, with a variation of just 2 miles per gallon. This is an impressive achievement for a large car. No errors or flaws, under any circumstances. Consistently performed oil and filter changes every 8,000 miles, with the most recent gearbox fluid replacement being in July of last year.

Approximately three weeks ago, I saw that the radiator fan was rapidly increasing its speed approximately 30 seconds after starting the engine. Despite the low outside temperature of 2C or 3C, I must admit that I did not immediately see a decrease in fuel efficiency. The engine temperature reaches its typical 90 degrees Celsius after about 15 minutes of driving. I am also certain that on one occasion, the fan did not rotate at all throughout my 40-mile journey back home. When I switch the engine to position 2, the fan ceases to operate. Therefore, it is not the issue of being continuously active.

I have perused the current discussions on the issues of a 'noisy fan' and 'radiator fan speed', as well as the solution using the AC Pressure Sensor. I am reluctant to visit that place only due to the decline in the economy. I would like to inquire if you believe that the excessive cooling from the fan is affecting the economy by preventing the engine from reaching its optimal temperature for fuel efficiency. Alternatively, it might be that the issue is with a different sensor that is more closely associated with the fuel system, and this sensor is in turn sending a signal to the Engine Control Unit (ECU) indicating a failure.

What I have seen is that my fuel efficiency number when the engine is cold is now beginning at 14.1 miles per gallon. I am very meticulous when it comes to monitoring fuel efficiency. I have noticed a recent change in the vehicle's behaviour, which makes me suspect that it could be entering a state of reduced performance, often known as limp mode, but I have not seen any noticeable decrease in engine power.

The scanner I now own is a Launch CRP129, which is said to be pretty simple. However, it is equipped with the latest files, and I would have expected it to be capable of detecting error codes. No fault codes are present. The only reference to any issue in the 'live stream' is found exclusively in the EGR section. The fault code "Y85 EGR cooler bypass switchover valve Fault. 53336/6058" indicates that the value of the switchover valve changes to 'OFF' while driving. Although others have brought up this point, they have not specifically addressed the problem of fan speed. I believe this is nothing.

Up to this point, I have replaced the coolant temperature sensor with an authentic component from Mercedes. Unaltered.

I brought the vehicle to my nearby diagnostic facility, where they had just passed the MOT despite the car having the same issue we had noted when scheduling the appointment. The diagnostic indicated a malfunctioning radiator fan controller, which is documented on the bill. I bought a Ridex fan shroud from Autodoc and installed it myself, but there was no difference - everything remained same.

Considering contacting the individual again to provide them with another opportunity to identify the issue, but uncertain owing to their prior incorrect diagnosis.

Opinions? Aside from the comment "god, that's a long post" 😉

[BENZE220AMG]

Retrieve real-time data from all the air conditioning and temperature sensors installed in the automobile. If you come across very low, high, or unrealistic figures, here is the area to investigate.

I saw a decrease in air conditioning pressure, which was later determined to be caused by a leak in the condenser. As a result, the fan consistently activates after a 10-second interval.

A friend of mine who owns an E250 recently had a similar issue, like yours. The problem turned out to be a damaged or frayed cable for one of the temperature sensors, albeit it was not located directly next to the sensor. However, the defect was identified using real-time data analysis, rather than relying on fault codes.

[ENVIOclev]

Could a high fan speed indicate a voltage issue? Have you inspected all the fuses and grounding connections? Battery voltage refers to the electrical potential difference across a battery, which is measured in volts. Charging voltage, on the other hand, is the specific voltage required to charge a battery and restore its energy levels.

[CelestialSeeker]

As you have seen, this may be attributed to a multitude of factors. In my opinion, it would be beneficial for you to seek out an independent mechanic that specialises in Star diagnostics. This will likely result in both cost savings and a reduction in future frustrations, since they would be very skilled in identifying and resolving the issue. Components are too costly to rely on trial and error.

[ElectricEclipse]

I appreciate the advice, gentlemen. The automobile has been scheduled for a second diagnostic test this week. Today, someone speculated, "Could the increased load from the fan running impact fuel consumption?" Undoubtedly, the answer is affirmative, since it must have an impact to a certain extent. However, is a 10% influence exceeding a reasonable proposition?

The primary battery has not been replaced throughout my ownership, indicating that it is likely the original battery. I replaced the battery situated in the boot on November 23rd.

[ElectricEclipse]

Experiment: Reduction in miles per gallon (MPG) due to increased fan speed. Prior to my daily journey, disengage the radiator fan. Result: The MPG decrease and unusual fluctuations in MPG from the initial values were consistent (beginning at 14.1mpg and progressively increasing to 14.9 -> 16.x -> 18.x -> 21.x over the following 3 to 4 miles). Initially, the automobile achieves a fuel efficiency of 31.x MPG within a short distance after leaving home. Shortly after, it reaches the mid 30's and within 5 miles it reaches the 40's. For most journeys, it consistently achieves fuel efficiency in the 50's. I see a significant decrease in fuel efficiency when encountering even the slightest incline, which then returns to normal while going downhill. Previously, there was a noticeable decrease in fuel efficiency of around 1 or 2 miles per gallon (MPG), but today the decrease is much more significant, with a reduction of 5 or 6 MPG per hill.

Last week, I conducted a comprehensive fuel efficiency test on my vehicle. Typically, I am able to travel a distance of 510 to 530 miles on a full tank of fuel, sometimes even surpassing this range. However, now, my vehicle is only able to cover a distance of 460 miles on a full tank.

According to the hypothesis, the same issue that is leading to the low fuel efficiency is also causing the ECU to receive data indicating the need for more cooling.

[KOOLCAR]

https://diysprinter.co.uk/reference/Introduction_OM_651.pdf

[KOOLCAR]

Examine the EGR Section. The bypass valve is operated using pneumatic means but is switched electrically, which means that a fault code may not always be generated in the event of a vacuum failure. The primary purpose of the EGR is to lower the temperature in the combustion chamber in order to decrease NOx levels. Therefore, there might be some kind of correlation between these two factors.

[ElectricEclipse]

Thank you, KOOLCAR, for providing such an outstanding material. If the orientation of the EGR unit aligns with the specifications mentioned in the datasheet, I may be able to do a partial inspection of the vacuum portion without much disassembly.