Short trips, low loads, and frequent engine shutdowns can hinder DPF regeneration. Learn how to operate a diesel forklift. Reading time: 6 minutes
Can a forklift have the wrong kind of work?
It can.
Not in the sense that the operator is using it against the instructions. Rather, it is about a situation where the machine is operated correctly, but its design does not fit the daily work rhythm.
A diesel forklift might be used for moving pallets between the warehouse and the loading bay, handling a construction site, loading production materials, or shifting heavy components around a plant. In such tasks, the engine runs for longer periods, the forklift covers greater distances, and it regularly works under load.
It might, however, also end up in a hall where it covers a distance of just a few metres all day long.
The operator lifts a light pallet, drives through a gate, places the load, switches off the engine, and restarts it after a few minutes. This happens dozens of times.
From the warehouse organisation's point of view, such a process can be completely normal.
From the diesel engine's point of view, it means operating under conditions that do not always allow it to reach the proper operating temperature and carry out a full cleaning of the exhaust system.
Therefore, the question should not be only: what lifting capacity should the forklift have?
Before choosing the drive, it is worth looking at the daily work rhythm.
The length of a single trip, the number of engine starts per day, the weight of the most frequently transported loads, and the location of the tasks all matter.
Different conditions prevail in a hall, where the forklift covers short sections and stops frequently, and different on a yard, where it works longer, under greater load and in a larger space.
It is also necessary to check whether the machine has the ability to carry out a full filter regeneration according to the manufacturer's recommendations. Only such a picture of daily operation allows for a sensible assessment of whether a diesel drive will be suitable for the given process.
Why does a diesel engine need temperature?
A diesel engine does not reach full efficiency immediately after starting.
After start‑up, the oil must reach all parts of the lubrication system, the engine must reach a stable temperature, and the exhaust gases must have the right parameters for the aftertreatment system to work correctly.
During intensive work, the engine produces more heat. The forklift lifts a heavy load, covers a longer distance, or works on a surface requiring greater tractive effort. Under such conditions, the drive system operates closer to the range for which it was designed.
With a short trip and a light load, the situation is different. The engine may be switched off before it reaches the temperature needed for stable operation. The next start begins another warm‑up cycle.
A single short cycle is not a problem. Every forklift can sometimes travel a few metres, make a quick manoeuvre, or be switched off after a short period of work. What matters is repetition.
If the engine operates in short cycles, at low load, for many hours, the entire system may have difficulty maintaining the conditions needed for correct operation.
This can be compared to heating a large building by turning a heater on and off frequently. Energy is consumed, but the temperature does not stabilise efficiently. In an engine, too, part of the energy is used just to warm up the system before the machine has done the work for which it was started.
What is the DPF?
DPF stands for Diesel Particulate Filter.
Its task is to trap soot particles produced during diesel combustion.
The filter is located in the exhaust system and gradually collects solid particles. It cannot, however, fill up indefinitely. Therefore, the control system monitors, among other things, the exhaust gas temperature and the pressure before and after the filter.
When conditions are right, the soot can be burned off during regeneration.
Passive regeneration occurs when the exhaust gas temperature during normal operation is high enough. In this case, the filter cleans itself gradually, without any obvious operator intervention.
If the temperature is too low, the system may initiate active regeneration. The engine controller then modifies the operating parameters to increase the temperature in the exhaust system.
The exact mode of operation depends on the engine and the exhaust aftertreatment system used. In the case of machines meeting Stage V requirements, the system may include several cooperating components, among them a particulate filter, an oxidation catalyst, temperature sensors and a differential pressure sensor.
Stage V sets requirements for emissions from non‑road mobile machinery engines. It does not, however, mean that the engine does not require proper operation. The exhaust aftertreatment system is part of the machine and must operate under the conditions foreseen by the manufacturer.
What do short trips have to do with the DPF?
Most often, the problem is not the length of the trip itself, but a combination of several factors.
The engine runs briefly. The load is low. The exhaust temperature remains low. The forklift stops frequently, and regeneration does not have time to complete fully.
In such a situation, soot can accumulate in the filter faster than it is burned off.
If the operator switches off the engine during regeneration, the process can be interrupted. Sometimes the system will resume it later. However, if similar situations occur regularly, the filter will gradually become more and more loaded.
Instructions for diesel engines often include a recommendation that, in the event of a specific message, the machine should be allowed to carry out regeneration in safe conditions. The forklift should then stand or operate according to the manufacturer's procedure, away from flammable materials and in a place with adequate ventilation.
A custom procedure should not be created based on experience with a passenger car. A forklift has different operating conditions, different loads and different safety requirements. The detailed rules should always be checked in the documentation for the specific model.
Does light work harm a diesel forklift?
Light work itself does not necessarily cause harm.
A diesel forklift can carry lighter loads for part of the day. Not every cycle has to use the machine's full lifting capacity. The problem arises when light work continues throughout the entire shift and is combined with short sections and frequent engine switching off.
For example, a company may need a 3.5‑tonne forklift because once every few hours it has to move a heavy production mould. For the rest of the day, the operator transports pallets weighing 400 kilograms.
Such a purchase may be justified, but it is worth analysing what most cycles look like. If the heavy task occurs only occasionally, and the daily work takes place in the hall over short distances, different solutions are possible.
One is to use an electric forklift for daily transport and keep the larger diesel forklift for tasks requiring greater lifting capacity.
Another solution may be to choose a single machine that will handle the entire process if the working conditions and costs justify such an approach.
There is no single answer for all plants. The important thing is not to buy a larger machine solely on the basis of the heaviest, but rarely performed, task.
Is idling a good solution?
Long‑term idling usually does not replace work under load.
The engine remains running, but produces less heat than when driving with a load and operating the hydraulic system. If the forklift stands for a long time with the engine running, it can consume fuel without any real progress in the process.
In practice, idling may be needed, for example during a short stop, waiting for documents, or preparing the next load. The problem is leaving the machine running for many hours without a clear need.
Long periods of idling also do not solve the DPF regeneration problem. If the manufacturer has specified a specific regeneration procedure, the operator should follow it, rather than trying to achieve the right conditions by randomly leaving the engine at idle.
What can a regeneration message mean?
A DPF message does not always mean a serious fault.
It may inform that the system wants to carry out regeneration, or that the accumulated soot level has exceeded the value at which operator action is needed.
Such messages should not, however, be ignored.
If the filter becomes more and more loaded, the controller may limit engine power. The forklift will then operate in a protective mode. It may accelerate more slowly, have reduced performance, or require a service visit.
The cause of the problem is not always the filter itself. Similar symptoms can be caused by faulty sensors, problems with injectors, the intake system, the EGR valve, or incorrect engine operating parameters.
Therefore, forcing regeneration without prior diagnostics is not always the right solution. If the cause remains unidentified, the filter may quickly become clogged again.
It is also worth remembering that regeneration involves a high exhaust system temperature. The forklift should not then be parked near dry materials, waste, wood, paper or other flammable items.
When does a diesel forklift make the most sense?
A forklift with a diesel engine works best when the operating conditions match its strengths.
This applies above all to outdoor applications, long shifts, heavy loads, uneven surfaces, and processes where high availability is important.
A diesel forklift can be a good solution in a production plant where materials are transported between several halls. It will also work well on a construction site, at a building materials depot, at a transhipment terminal, or in a plant that regularly handles heavy components.
Under such conditions, the forklift does not only perform a short manoeuvre. It works continuously, covers greater distances and more often uses engine power.
This is why the model is selected for the process, not only for the maximum load weight.
A 2.5‑tonne forklift in a production plant
Imagine a plant where pallets of components are transported between the warehouse and the production line. The distance is about 150 metres. The forklift works two shifts, and most loads weigh from 800 kilograms to 1.8 tonnes.
In this case, a 2.5‑tonne forklift may have an appropriate margin of capability. However, the type of surface, aisle width, lift height and number of cycles per hour will also be important.
The MFD 25 can be considered, in such an example, as a machine for regular work with loads of average weight, especially if part of the operations are carried out outdoors or in conditions requiring an internal combustion drive.
If, however, the same forklift were to handle only a few metres inside a heated hall, and the loads weighed at most 300 kilograms, the analysis could lead to a different conclusion.
The same lifting capacity does not mean the same application.
A 3.5‑tonne forklift for heavier components
Assume that a plant produces large steel components. Some loads weigh over 2 tonnes, and some are long and require proper stability during lifting.
In this case, not only the weight matters, but also the centre of gravity, load geometry and lift height.
The MFD 35 can be analysed as an example of a 3.5‑tonne forklift intended for heavier industrial tasks.
If such a forklift works outdoors, covers longer distances and regularly lifts heavy components, the application profile is consistent with the character of the diesel drive.
If, however, heavy components appear only once a week, and for the rest of the time the machine performs short trips around the hall, it is worth calculating whether buying a large forklift as the main machine is really the most efficient approach.
A 5‑tonne forklift in a heavy working environment
In a concrete prefabrication plant or a steel processing company, moving heavy components can be a daily occurrence.
Loads weighing several tonnes require appropriate lifting capacity, stability and space for safe manoeuvring. In such an environment, a diesel forklift can work for many hours, often outdoors and under high load.
The MFD 50 is an example of a 5‑tonne machine that can be considered for handling heavy moulds, concrete elements, castings, dies or large material packages.
In such an application, the question of short trips is less relevant, because the load and operating time are usually greater. However, the rules concerning maintenance, regeneration and safe parking still need to be followed.
A large lifting capacity does not exempt from proper operation. On the contrary, with heavy machines, the consequences of neglect can be more noticeable.
A 5-ton MFD 50 diesel forklift transports heavy concrete elements at a precast concrete plant. CC: Müeller Machinery 2026
Diesel or electric for short trips?
If the forklift works mainly indoors, covers short distances and stops frequently, an electric drive may be worth careful consideration.
An electric forklift has no internal combustion engine or DPF, so the problem of soot regeneration disappears. This does not mean there are no operational requirements. Charging must still be planned, battery condition monitored, ambient temperature taken into account, and whether one battery will last the entire shift determined.
An electric forklift can also operate more quietly and does not emit exhaust gases directly in the hall. This can be important for operators and people working nearby, especially during long indoor work.
Diesel, on the other hand, will often be a better solution outdoors, with heavy loads, uneven surfaces and long working hours without charging breaks.
There is no point in deciding this question on the basis of a general slogan that one drive is more modern than the other. Modernity also consists in matching the technology to the conditions.
How to analyse the working profile before buying a forklift?
It is best to start by observing one typical shift.
It is worth checking how many times the operator starts the engine, how long the average trip lasts, what loads are most often transported, and for how long the forklift works without stopping.
The location of the tasks, the type of surface, and whether the machine covers longer sections between successive work points also matter.
It will be helpful to divide the tasks into three groups: daily repetitive operations, heavier work performed occasionally, and emergency and unusual situations.
Such an analysis allows an assessment of whether the company needs one universal machine, several forklifts with different drives, or a model matched primarily to the most important process.
Service availability, spare parts availability and response time should also be considered, because the cost of downtime can quickly exceed the difference in purchase price between two similar machines.
Common questions about diesel engines and DPF filters also arise at this point.
Does every diesel forklift have such a filter? No, because the exhaust aftertreatment system depends on the specific engine, its power and the machine configuration.
Can a short trip damage the filter? Not by itself, however many hours of operation in short cycles, at low load and with frequent engine switching off can make it difficult to reach the temperature needed for proper regeneration.
Is leaving the forklift idling enough to carry out this process? Not always. The regeneration method depends on the design of the given model, so the operator should follow the manufacturer's instructions and respond to system messages.
If the forklift works mainly indoors, covers short distances, stops frequently, and its loads are light, it is worth comparing diesel drive with electric.
An electric forklift can, in such conditions, provide quieter operation and the absence of local exhaust fumes.
Diesel will retain its advantage for heavier tasks, longer routes, outdoor work and greater loads. The answer therefore comes from the plant's daily rhythm, not from the drive name alone.
Diesel and electric forklifts: how to match the drive to the work?
Diesel forklifts are important, especially where the machine works outdoors, handles heavy loads and remains in motion for most of the shift.
In many plants, however, the best results come from a combination of different drives.
Diesel can handle truck loading, materials transport around the yard and heavier industrial tasks, while an electric forklift will be better suited inside the hall, for short trips, frequent stops and work in the presence of people.
Therefore, when choosing, it is worth looking more broadly than just the lifting capacity.
The length of routes, number of cycles, operating time per shift, type of surface, load weight, environmental conditions and service access all matter.
Every plant has its own work rhythm, different routes, loads and constraints, so a well‑chosen machine should result from real needs, not a universal template.
Müller Machinery offers solutions for different environments and applications, from diesel forklifts for demanding industrial work to electric models intended for indoor tasks.
We encourage you to browse the full range of Müller Machinery forklifts and to contact us if you need to translate your process requirements into a specific machine configuration.
We also invite you to discuss practical solutions on the Müller Machinery LinkedIn profile, where we share knowledge about materials handling, machinery and the realities of working in an industrial environment.
Sources: Regulation EU 2016/1628, Ford Service Content dotyczący filtra DPF, Snap on Diagnostics o regeneracji i diagnostyce DPF.