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The lowdown - why operating in low load mode can be harmful to your generator

Updated: Nov 9, 2020

Did you know?

Endothermic engines in generators are designed to use as much power as possible, with 30-100% of the declared maximum power recommended.

Actual engine load varies depending on the power that an installation demands. However, generator engines and components are primarily designed to operate in high load or power range as opposed to continuous low load mode.

What are effects of operating in low load mode?

1. Higher oil consumption

Operating uninterruptedly in low load mode can lead to higher oil consumption and thus a greater deposit of carbonized oil or oil residue in the engine, as well as in the suction and exhaust system.

2. Higher hydrocarbon emissions

When running in low load mode, a system cools down, meaning its fuel is only partially burned, which in turn can lead to a white smoke being produced with high hydrocarbon emissions.

3. Reduced fuel quality

In low load mode, a low fuel temperature means the percentage of unburned fuel in the oil increases. This is because the piston rings, the piston itself and the cylinder do not dilate enough to ensure a good seal causing the oil to rise and expel through the exhaust valves. Diesel oil then passes into the crankcase, degrading the quality and the properties of the fuel.

4. Other issues

Continuous use of low power mode can cause various problems for generators over time, including:

· Increased exhaust smoke

· Increased pressure in gearbox and crankcase

· Traces of fuel found in engine oil

· Excessive wear of turbocharger

· Oil leaks in the turbocharger

· Deposit of carbon residue on valves, valve seats, pistons and exhaust manifold

· Hardening of surfaces on cylinder liners.

How to avoid/correct low load mode

To ensure correct use of your generator set, PPSPower recommends avoiding operating it uninterruptedly in low load mode or reducing low load usage to minimum periods of time (ideally 5 minutes or less).

During weekly operational testing, no-load operating time should be limited to a maximum of 5 minutes, until the generator set’s battery charge values return to normal.

Load bank testing

A generator set should be operated at least once a year for an hour (or several hours depending on size) at full load to clean the engine and eliminate the carbonized oil deposits in the engine and exhaust system. This may require a load bank. The load should be increased over a four-hour period of operation, from zero to full load.

To correct the issues mentioned above, PPSPower recommends operating the generator at full load, if possible using a Resistive Load Bank, before replacing any components.

Contact PPSPower to discuss your maintenance needs

PPSPower offers first-class professional generator servicing and UPS services, with over 60 years’ combined experience and a 24/7 call out facility from engineers based throughout the UK. All service packages come with a dedicated account manager to ensure requirements are understood and dealt with effectively, and a bi-annual generator service visit with relevant system checks. To schedule a professional generator service or discuss available packages, visit

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