Guide
Generator Fuel Consumption Per Hour
Fuel use is decided by the load the generator actually carries, not by the size printed on the canopy. This page explains how the figure is read from the engine data and the load, and what makes a set drink more than it should.
- Worked out from the plate and the load
- No single litres-per-hour figure for all sets
- Rising consumption is treated as a fault
- Onsite across Gauteng
How it is calculated
Load decides the fuel, not the kVA on the plate
A generator only burns fuel for the power it is producing. A 100 kVA set carrying 25 kVA does not use the fuel of a 100 kVA set at full output. This is why a single litres-per-hour number for a size of machine is misleading, and why ProService Generator Repairs reads the data plate and the actual load before discussing running cost.
The honest way to estimate it is from the engine manufacturer’s fuel curve for that model, at the load the site really draws. Most diesel engine datasheets publish consumption at 25, 50, 75 and 100 percent load. Those published figures belong to the engine, not to this page, so the model and the load are what get looked up.
Where consumption matters commercially, a load bank test gives the output and the behaviour under a controlled load instead of an assumption. That is a separate visit and it is described on the load bank testing page.
What changes it
What actually moves fuel consumption
These are the things a technician looks at when a set starts using more fuel than it used to.
The load being carried
The single biggest factor. Fuel use rises with the kW the alternator is actually delivering, so the same machine costs different amounts to run on different days.
Running at light load
A diesel carrying very little load runs cooler than intended and is less efficient per unit of power. Long periods at light load also cause glazing and wet stacking, which is an engine problem, not just a cost problem.
Engine condition
Worn injectors, a tired fuel pump and poor compression all raise consumption. This is why a sudden rise in fuel use is investigated as a fault rather than accepted.
Air and exhaust restriction
A blocked air filter or a restricted exhaust makes the engine work harder for the same output. Both are checked on a service.
Fuel quality
Contaminated or degraded diesel burns poorly and can also blur the picture by blocking filters. Stored standby fuel is covered on the contaminated diesel page.
Governor and speed
An engine not holding its set speed is not running at its designed operating point. Frequency and speed are measured rather than assumed.
Working it out
How to get a usable figure for your set
Read the data plate
Note the kVA, the power factor and the engine make and model. The engine is what burns the fuel, so the engine model is the part that matters for a fuel figure.
Find the real load
Read the load on the controller while the set is running, or have it measured. Without this the consumption question has no answer.
Use the engine fuel curve
Look up the manufacturer consumption for that engine at that load percentage. Use the figure published for your model instead of a generic table.
Compare with the tank
Track litres used against running hours on the controller. A drift away from the expected figure is the signal worth acting on.
Treat a rise as a symptom
Consumption climbing on the same load pattern points at the engine, the fuel or a restriction. That is a diagnosis, booked as a repair.
Keep the record
Hours and litres recorded at each service make the next comparison meaningful. Running hours are explained on their own page.
Common Questions
Generator fuel consumption — questions
How many litres per hour does a generator use?
It depends on the engine and the load it is carrying, so a single figure cannot be given for a size of generator. The usable number comes from the engine manufacturer’s consumption data at the load percentage your site actually draws.
Does a bigger generator always use more fuel?
Not for the same load. A larger set carrying a small load can be inefficient per unit of power, and long periods at light load bring their own engine problems. Sizing is matched to the load, which is covered on the generator sizes page.
Why is my generator suddenly using more fuel?
On an unchanged load pattern, a rise usually points at injectors, the fuel pump, compression, a blocked air filter, a restricted exhaust or poor fuel. It is diagnosed on the set rather than estimated.
Is running a diesel generator at low load a problem?
Yes, over time. A diesel held at very light load runs cooler than designed, which encourages glazing and wet stacking. Load bank testing is one way to exercise a set properly.
Can you tell me my running cost over the phone?
Not reliably. The engine model and the measured load are needed first. Those can be read off the plate and the controller, and a photo of both is useful.
Does servicing reduce fuel consumption?
A service restores the things that raise consumption when they are neglected, such as air filtration, fuel filtration and general engine condition. It does not change the fuel a given load requires.
Still unsure what the fault is? Call or WhatsApp 082 057 4605 for onsite diagnosis.
Related Pages
Load, sizing and the systems that affect fuel
- kVA to kWReading the rating correctly
- Generator SizesMatching the set to the load
- Load Bank TestingOutput under a controlled load
- Running HoursHours against litres over time
- Fuel System RepairsFilters, pumps and delivery
- Injector ServiceInjectors that affect burn
- Black SmokeBurning fuel badly under load
- Generator ServicingAir, fuel and oil on schedule
- Generator GuidesThe rest of the practical guides
Service Areas
Onsite visits across Gauteng
Technicians travel to the generator. These are the main Gauteng areas. Suburb pages sit under each region.
What to send before we attend
ProService Generator Repairs confirms an onsite visit from these details. Send what you have. A missing model number does not stop the booking.
- Location
- The suburb or site, so the visit can be booked in the right area.
- Make and model
- The generator brand and model, if they are known.
- kVA
- The size printed on the data plate.
- Fuel type
- Diesel, petrol, LPG, natural gas, or dual-fuel.
- Controller model
- The module name on the panel, when it is visible.
- Fault or alarm
- What the set does, and any text on the screen.
- Photos
- The generator, the data plate, and the controller or alarm. Send these on WhatsApp.
Book a Visit
Send the data plate and the load
A photo of the data plate and the controller reading is enough to start. The engine model and the measured load decide the fuel figure.
- Call
- 082 057 4605
- Message us on WhatsApp