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Apologies for the lengthy article.

In March, I acquired a 2019 C300d and as part of the process, I took it on a test drive, among other things. I examined the fuel efficiency over an extended period of time. The vehicle achieved a fuel efficiency of 55 miles per gallon over a distance of 8,000 miles, which pleasantly surprised me. Based on the car's impeccable condition and the additional features that were installed, I might infer that it was formerly owned by an individual who cherished it. However, I am uncertain about the manner in which it was driven.

On the day I acquired the automobile, I embarked on a substantial drive mostly consisting of travelling at speeds over 50 miles per hour on both dual carriageways and motorways. Despite my efforts to drive conservatively, I had difficulty in achieving a fuel efficiency of more than 35 miles per gallon. During my subsequent visit to the dealer, I brought up this matter and expressed my intention to observe its progress. Initially, the performance was satisfactory for a few weeks, and I consistently achieved an average fuel efficiency of 50 miles per gallon throughout my 40-mile commute to work on the M6 highway, which pleased me. Subsequently, the fuel efficiency of the vehicle unexpectedly decreased to 35 miles per gallon over the same trip. However, the car continued to operate normally, and the issue resolved itself later in the evening. Consequently, I disregarded the matter. Nevertheless, I have since had this problem numerous times during similar trips under comparable circumstances. I drive my vehicle just once or twice a week, but these trips are usually longer in distance. They often begin with a 1-2 mile drive on a 50mph dual carriageway, allowing the car to gradually warm up and have a satisfactory journey. Occasionally, I provide the hard drive with a significant workload, without causing excessive strain. However, most of the time, I focus on monitoring the economy meter and maintaining a steady performance. I do not spend time socialising or participating in activities like as joining motorways, etc.

Subsequently, in the previous month, I saw that while first starting the vehicle and attempting to accelerate, it has a brief period of hesitation and lacks sufficient power. There are no error messages or warning lights shown on the dashboard, and the vehicle operates normally for the remainder of the day, even after being parked for 8 hours at the office. To confirm, I conducted a test by starting the vehicle and trying to gradually increase the engine speed, rather than driving away. The identical issue occurred, indicating that it was not due to the gearbox. Based on my observations, I have a suspicion that the glow-plugs or controller may be the cause of the issue. However, I decided to take the vehicle to Mercedes, since it is still under warranty. After their inspection, they discovered a damaged hard pipe near the air box and replaced a NOx sensor.

At first, the automobile seemed to be repaired, and when I drove it again, there was no stuttering. On the day I went to the office, the situation was really bad. It persisted till the end of our road, which measures around 80 meters. However, for the remainder of the day, everything was good. I made a reservation for it before, but it did not function properly on subsequent rides, until Saturday. Initially, the vehicle performed optimally for a brief period of time. However, I was unable to achieve a fuel efficiency of more than 35 miles per gallon when driving at a steady speed of 30 to 50 miles per hour in gears 5 to 7. The fan returned to its maximum speed, but there was no sound coming from the exhaust. Once again, the same situation occurred the next day on a 7-mile trip when I maintained an average speed of 50mph, resulting in a fuel efficiency of 24.5mpg.

Yesterday, the morning started well and I proceeded to commute to work, covering the customary distance of 40 miles at a fuel efficiency rate of 50 miles per gallon. Upon leaving work to go to Mercedes, I had a momentary hesitation in my vehicle, which was the first occurrence of this issue after driving earlier in the day. I travelled to Mercedes and it achieved an impressive fuel efficiency of 56.5 miles per gallon, even in the presence of a traffic congestion.

Earlier today, I received a call informing me that there were no issues with the vehicle. We proceeded to take it for a drive, during which a Diesel Particulate Filter (DPF) regeneration occurred. Despite being monitored by them, the automobile nevertheless managed to attain a fuel efficiency of 35 miles per gallon (mpg). 'This is the reason why your fan was operating throughout the weekend.' Considering that I had only travelled less than 100 miles since Sunday, this seemed incorrect to me, particularly since it should have occurred during the previous night's journey.
They had forgotten about the first problem and claimed that there was no issue. However, I informed them that if the vehicle had been started before they completed their seatbelt and mirror inspections, the problem may have already been resolved. They will inspect this later, but I believe the vehicle will still be very heated.

Has anybody else encountered these issues? Does a Diesel Particulate Filter (DPF) regeneration process really last for many hours and significantly reduce fuel efficiency? Is this frequency of occurrence appropriate? I regret not keeping the previous vehicle when it had reached 115,000 miles, even if it required replacing the NOx sensor again, rather than going through the current situation. I am pleased that I purchased the second year of the MB warranty at a low cost when I acquired the vehicle.

This does not seem to be accurate to my understanding. In the past, I had a Mercedes car that ran on petrol and experienced a hesitation issue, which was ultimately diagnosed as a malfunctioning Mass Air Flow (MAF) sensor. Uncertain if the diesel engine is equipped with a Mass Air Flow (MAF) sensor considering the current "dieselgate" technology.

In my opinion, if you have not yet done so, I would recommend using a potent diesel fuel additive, such as Redex Diesel Injector Cleaner or Millers Diesel additive, to thoroughly clean and purify the injectors and fuel system. Then provide standard dosages regularly.

What is the car's mileage?

Achieving a fuel efficiency of 55 miles per gallon over a distance of 8000 miles indicates that the vehicle was likely operated in favourable circumstances and was not subjected to excessive strain. A DPF regeneration significantly affects fuel consumption, although it should not take a long time. It is hard to provide an exact duration, but it typically lasts about 10-20 minutes. The length of the object may vary based on many factors such as the level of blockage and temperature.

If they are asserting that there is 'nothing wrong', it might be inferred that no error codes were shown on the STAR system, which provides little assistance. What is the temperature shown by the gauge under typical operating circumstances and how rapidly does it increase?

It is possible that the issue lies with a defective NOx sensor, however there might also be a range of other sensors causing the problem. A practical recommendation would be to use a diesel cleaner additive or fill the tank with high-quality diesel fuel such as Shell V-Power diesel. This approach aims to assess if these measures can effectively address the issue at hand.

Additionally, there are dpf-cleaner gasoline additives available for purchase. However, I lack personal knowledge with these and cannot verify their effectiveness.

Regarding dpf regenerations, it can be quite troublesome, especially if the process is interrupted midway. It would be highly beneficial if car manufacturers installed a notification light to inform the driver when the regeneration is taking place. This would be in line with the practice of incorporating lights and buzzers for various other purposes in modern vehicles.

I recently retrieved it and when starting it, it immediately had a little hesitation before running well. As a traditional engineer, I really dislike the fact that dealers just rely on the information provided by digital diagnostics. If the warranty did not cover it, I would inspect the components in the engine compartment that might potentially be causing this issue.

The car has accumulated a mileage of 43,000 miles. The engine temperature consistently remains at 90 degrees and reaches this level after a few minutes of starting the car. Once the temperature reaches the desired level, the performance of the vehicle is flawless. There is certainly no shortage of power when I engage the highest gear and accelerate to the maximum.

The vehicle may be fuelled with either Costco Diesel, which I have used without any issues for 6 years in my 250d, or Shell Diesel as a last resort. I must confess to feeling cautious about cleaners and similar professionals. We used a Redex cleaning to the wife's Fiesta Zetec TDCi, which subsequently caused it to emit smoke indefinitely.

Previously underwent a replacement of the EGR valve, indicating a past occurrence of some form of problem. In general, my average fuel efficiency is now 44.3 miles per gallon over a distance of almost 3,000 miles. This is acceptable, and on a holiday trip in May, it reached 56 miles per gallon. However, I have a strong suspicion that there is a problem with the vehicle's starting mechanism, among other potential issues. I want to record the hesitation at the very least, in order to provide visual evidence that I am not mentally unstable.

In a few weeks, we will be embarking on a 600-mile journey, which will provide us with a more comprehensive understanding of the overall performance and ensure that everything is thoroughly tested.

I had a similar stuttering issue when my 250CDI OM651 engine was exposed to low temperatures, albeit it is obviously a different engine. The problem has been resolved by replacing the exhaust pressure sensor located in the engine compartment.

I would suggest putting the transmission into sport or manual mode and sometimes use the whole range of engine revolutions, rather than consistently hypermiling at low RPMs. This approach promotes healthy driving habits.

In my opinion, I had a preference for my OM651 250d, despite its somewhat rougher nature.

It occurred again yesterday morning before to a satisfying drive down the M6. I used the Sport+ mode on a few occasions and applied significant acceleration, which undoubtedly caught the Integra Type-R off guard when we transitioned onto the highway. The Integra Type-R was unable to distance itself until I reached a speed of 70 and began cruising.