Running In a New Generator: A Complete Guide for Petrol and Diesel Models

Buying a new generator is an investment, whether you need reliable power for a construction site, workshop, home backup, farm, event or leisure application.

One of the most important steps after purchasing a new generator is running it in correctly.

The running-in period allows the engine's internal components to bed in gradually during the first few hours of operation. This can help promote reliable performance, reduce premature wear and ensure the generator is properly prepared for normal use.

Whether you have purchased a petrol generator, diesel generator, inverter generator or larger three-phase model, following the manufacturer's running-in guidance is essential.

In this guide, we explain how to run in a new generator, what to avoid during the first few hours, when to change the oil and how to prepare your generator for long-term use.

You can also explore our full range of Petrol Generators, Diesel Generators, Inverter Generators and Three-Phase Generators.

What Does Running In a Generator Mean?

Running in, sometimes called breaking in, is the initial operating period of a new engine.

During manufacturing, internal engine components are produced to very close tolerances, but they still need a short period of controlled operation to settle correctly.

Components such as piston rings, cylinder surfaces, bearings and other moving parts begin to bed in during these first operating hours.

A careful running-in process can help:

• Promote correct engine bedding

• Reduce unnecessary early wear

• Improve long-term reliability

• Support consistent oil consumption

• Help the engine operate smoothly

• Identify any early faults

• Prepare the generator for normal working loads

The exact running-in procedure varies between manufacturers and models, so the owner's manual should always take priority over general advice.

Read the Generator Manual First

Before adding fuel or starting a new generator, read the manufacturer's operating instructions.

The manual should explain:

• Correct fuel type

• Recommended engine oil

• Oil capacity

• Initial oil change interval

• Starting procedure

• Running-in recommendations

• Maximum loads

• Maintenance intervals

• Safety requirements

Do not assume that two generators with similar engines have identical running-in procedures.

Some manufacturers may specify a particular initial service interval or recommend avoiding sustained maximum load during the first few hours.

Always follow the instructions supplied with your exact generator model.

Check the Engine Oil Before Starting

Many new generators are shipped without engine oil.

This is extremely important.

Never assume a brand-new generator has already been filled with oil.

Before the first start, check the oil level and add the correct grade if required.

Running an engine without sufficient oil, even for a short period, can cause serious damage.

Position the generator on a level surface and fill the engine according to the manufacturer's instructions.

Use only the recommended oil specification and quantity.

Do not overfill the engine.

Many modern generators also include low-oil shutdown protection, but this should never be relied upon instead of checking the oil manually.

Add Fresh, Correct Fuel

Use fresh fuel of the correct type.

For a petrol generator, use the petrol specification recommended by the manufacturer.

For a diesel generator, use clean diesel from a suitable source.

Avoid using old fuel that has been stored for long periods.

Contaminated or degraded fuel can cause poor starting, rough running and fuel system problems.

If you have purchased a new Petrol Generator, only add fuel once the generator is positioned safely outdoors and the engine is cool.

Never refuel a running or hot generator.

Inspect the Generator Before First Use

Before starting the generator for the first time, carry out a basic visual inspection.

Check:

• Engine oil level

• Fuel level

• Fuel cap

• Electrical outlets

• Cables

• Frame

• Wheels

• Handles

• Battery connections

• Loose bolts

• Transport damage

If the generator has been delivered on a pallet or through a courier network, inspect it carefully before use.

Make sure all packaging, transport brackets or protective materials have been removed where required.

If anything appears damaged or loose, resolve the issue before starting the generator.

Position the Generator Safely

Combustion generators must be operated outdoors.

Never run a petrol or diesel generator inside a home, garage, shed, vehicle, tent or other enclosed space.

Generator exhaust contains carbon monoxide, which is colourless, odourless and potentially fatal.

Position the generator in accordance with the manufacturer's safety guidance, away from doors, windows and ventilation openings.

Also ensure:

• The surface is stable and level

• Airflow around the engine is unrestricted

• Exhaust gases can disperse safely

• The generator is protected appropriately from weather

• Electrical connections are kept dry

Correct positioning is essential during both running-in and normal operation.

First Start: Run the Generator Without Load

For many portable generators, a sensible first step is to start the engine with no electrical equipment connected.

Follow the manufacturer's exact starting procedure.

For a petrol generator, this may involve:

• Opening the fuel valve

• Switching the ignition on

• Setting the choke

• Using recoil or electric start

• Moving the choke gradually to the run position

For diesel generators, the starting procedure may involve preheating, battery starting or other controls depending on the model.

Once the engine starts, allow it to stabilise.

Do not immediately connect a large electrical load.

Listen for unusual noises and check for:

• Fuel leaks

• Oil leaks

• Excessive vibration

• Warning lights

• Abnormal exhaust smoke

If anything appears unusual, shut the generator down and investigate before continuing.

Should You Let a New Generator Idle for Hours?

Generally, simply leaving a new generator running under no load for hours is not necessarily the best running-in approach.

An engine benefits from operating under varying conditions rather than remaining completely unloaded for an extended period.

However, the correct procedure depends on the manufacturer.

A short warm-up period without load is usually appropriate before gradually introducing electrical loads.

Avoid assuming that "the longer it idles, the better it is."

Extended no-load operation may be undesirable on some engines, particularly larger diesel models.

Always follow the manufacturer's instructions.

Introduce Light Loads Gradually

Once the generator has warmed up and is operating normally, light electrical loads can usually be introduced.

The aim during the early running period is generally to avoid placing the engine under immediate maximum stress.

Start with a modest load.

For example, you might begin with lighting or another relatively low-demand appliance rather than immediately connecting equipment requiring the generator's full rated output.

Gradually varying the load allows the engine to operate across different conditions.

Do not exceed the generator's rated capacity.

Avoid Sustained Maximum Load During Running-In

During the first few hours, it is generally sensible to avoid operating the generator continuously at maximum rated load unless the manufacturer specifically states otherwise.

High sustained loads place more thermal and mechanical stress on a new engine.

A gradual introduction to working loads allows internal components to bed in under controlled conditions.

This does not necessarily mean the generator cannot handle meaningful loads during running-in.

The objective is to avoid unnecessarily pushing a brand-new engine to its limits immediately.

For commercial or construction applications, plan the first operating period accordingly.

Vary the Electrical Load

Running the generator at exactly the same load continuously during the entire running-in period may not be ideal.

Where appropriate, vary the electrical demand.

For example:

• Start at a light load

• Increase to a moderate load

• Reduce the load

• Allow the engine to stabilise

• Increase again within safe limits

This creates changing engine speeds, combustion pressures and operating conditions where the generator design allows it.

Some inverter generators automatically adjust engine speed according to electrical demand.

If you have purchased an Inverter Generator, follow the manufacturer's guidance regarding economy or eco modes during the running-in period.

How Long Does It Take to Run In a Generator?

There is no universal running-in period.

It varies depending on:

• Engine manufacturer

• Generator model

• Engine size

• Petrol or diesel fuel

• Application

• Manufacturer recommendations

Some small engines may have a relatively short initial service interval, while larger commercial engines may have different requirements.

The owner's manual is the definitive source.

Rather than relying on a fixed number of hours from another generator, follow the instructions for your exact model.

The First Oil Change Is Important

The initial oil change can be one of the most important parts of running in a new generator.

During the early operating period, extremely small metallic particles can be produced as internal engine surfaces bed together.

Changing the oil at the manufacturer's specified initial interval removes contaminants from the lubrication system.

The first oil change may be required much earlier than future oil changes.

For example, the manufacturer's initial oil-change interval could be significantly shorter than the regular service interval.

Do not skip this first service.

Check the manual and make a note of the engine hours when the generator is first commissioned.

Keep Track of Running Hours

Many generators include an hour meter.

If yours does, record the engine hours from the beginning.

This makes it easier to schedule:

• Initial oil change

• Regular oil changes

• Air filter servicing

• Fuel filter replacement

• Spark plug replacement

• Commercial servicing

If your generator does not have an hour meter, keeping a written usage record can still be useful.

For business and construction users, logging engine hours can make generator maintenance much easier.

Check the Oil Regularly During Running-In

Oil consumption can sometimes be slightly different during the early stages of engine life.

Check the engine oil frequently during the running-in period.

Make sure the generator is on a level surface and follow the manufacturer's oil-checking procedure.

Never allow the oil level to fall below the safe operating range.

If the generator uses noticeably excessive oil or produces unusual exhaust smoke, stop using it and seek technical advice.

Running In a Petrol Generator

Petrol generators are widely used for trade, construction, home backup, camping and leisure applications.

Explore our Petrol Generators for models across a range of power outputs.

When running in a new petrol generator:

• Use fresh petrol

• Check the correct engine oil

• Start with no electrical load

• Allow a short warm-up

• Introduce loads gradually

• Avoid continuous maximum load

• Monitor oil level

• Complete the initial oil change

• Follow the manufacturer's service schedule

Petrol engines are relatively straightforward, but correct early maintenance can significantly affect long-term reliability.

Running In a Diesel Generator

Diesel generators are commonly selected for longer-running, commercial and industrial applications.

Our Diesel Generators include models suitable for construction, agriculture, business backup and industrial power.

Diesel engines should also be run in according to the manufacturer's instructions.

Avoid extended inappropriate low-load operation on larger diesel generators.

Diesel engines are often designed to work under meaningful load, and prolonged very light loading can sometimes create problems.

For larger commercial diesel generators, professional commissioning may be appropriate.

This is particularly important for standby systems and installations connected to buildings.

Running In an Inverter Generator

Inverter generators are popular because they combine portable engine-driven electricity with clean and stable electrical output.

They are widely used for:

• Camping

• Caravans

• Motorhomes

• Events

• Sensitive electronics

• Home backup

• Mobile working

When running in a new inverter generator, the basic engine principles still apply.

The engine contains oil, filters, fuel and moving components just like a conventional generator.

However, inverter generators may include economy modes that automatically change engine speed according to electrical demand.

Check whether the manufacturer recommends using or disabling economy mode during the initial running period.

Browse our Inverter Generators for compact and quiet portable power options.

Running In an Open Frame Generator

Open Frame Generators are commonly used for construction sites, workshops, farms and trade applications.

They are designed for robust working environments but should still be treated carefully during the first operating hours.

Do not assume a heavy-duty appearance means the generator can immediately be operated continuously at maximum load from new.

Follow the recommended running-in process and initial service schedule.

Construction businesses should also inspect the generator regularly for dust, debris and loose components.

Running In a Three-Phase Generator

Three-phase generators may supply 400V machinery, workshops, site distribution systems and industrial equipment.

Browse our range of Three-Phase Generators if you require commercial or industrial power.

Running in a three-phase generator should be approached carefully because loads can be considerably larger than on small portable machines.

Ensure:

• Loads are correctly sized

• Phase balance is considered

• Cables are suitable

• Distribution equipment is appropriate

• The generator is not overloaded

If the generator is being connected into a commercial electrical system, professional installation and commissioning should be used.

Do Not Overload a New Generator

Overloading is harmful to any generator, but it is particularly undesirable during the running-in period.

Never exceed the rated output.

Remember that some electrical equipment requires significantly more power when starting than when running.

Examples include:

• Compressors

• Pumps

• Refrigerators

• Air conditioning equipment

• Electric motors

• Power tools

A generator that appears large enough based only on running wattage may still struggle with start-up demand.

Always account for starting current when sizing electrical loads.

Allow the Generator to Warm Up

Avoid placing a cold engine immediately under heavy load.

After starting, allow the engine a short period to stabilise and reach operating condition.

Warm-up requirements vary by generator, so follow the manual.

Likewise, do not immediately switch off a heavily loaded generator.

Many manufacturers recommend removing the electrical load and allowing the engine to operate briefly before shutdown.

This can help temperatures stabilise.

Use the Correct Shutdown Procedure

Correct shutdown is just as important as starting.

A typical shutdown procedure may involve:

1. Disconnecting or switching off electrical loads.

2. Allowing the generator to run briefly with no load.

3. Switching off the engine.

4. Closing the fuel valve where applicable.

The exact process differs between generators.

Following the correct shutdown procedure reduces stress on both the engine and electrical equipment.

Do Not Constantly Start and Stop the Generator

Repeated short runs are not ideal during the running-in period.

Where practical, allow the engine to reach normal operating temperature before shutting it down.

Very short operating cycles may prevent the engine from warming properly.

This is particularly relevant to larger diesel generators.

Instead of repeatedly starting the machine for a few minutes, use sensible operating periods in accordance with the manufacturer's guidance.

Watch for Leaks and Loose Components

New generators should be inspected during the first several operating hours.

Vibration can sometimes reveal loose fasteners or fittings.

Look for:

• Engine oil leaks

• Fuel leaks

• Coolant leaks on liquid-cooled models

• Loose bolts

• Loose battery terminals

• Abnormal vibration

• Damaged hoses

If you discover a significant leak, switch the generator off and resolve the issue before continuing.

Listen to the Engine

Become familiar with how your new generator normally sounds.

During the running-in period, listen for:

• Knocking

• Metallic noises

• Unusual rattles

• Severe surging

• Irregular engine speed

• Excessive vibration

Some variation in engine speed may be completely normal, particularly on inverter generators responding to changing electrical loads.

However, persistent unusual mechanical noises should be investigated.

Check Electrical Output

Make sure electrical equipment operates normally when connected.

If the generator has a voltage display, monitor the output.

Do not continue using the generator if you notice:

• Severe voltage fluctuations

• Repeated circuit breaker trips

• Overload warnings

• Electrical burning smells

• Damaged sockets

For larger three-phase installations, electrical testing should be undertaken by a competent person.

After the Running-In Period

Once the initial running-in period and first service have been completed, the generator can normally enter its standard operating and maintenance schedule.

Continue to:

• Check oil levels

• Use clean fuel

• Replace filters

• Inspect the battery

• Keep cooling vents clean

• Test the generator regularly

• Record running hours

• Follow service intervals

Running in is only the beginning of good generator ownership.

Long-term reliability depends on regular maintenance throughout the generator's life.

What If the Generator Is Only for Emergency Backup?

A new generator purchased for emergency backup still needs to be commissioned and tested before it is relied upon.

Do not buy a generator, leave it boxed or unused for months and assume it will work perfectly during a power cut.

Set it up correctly.

Complete any required running-in procedure.

Carry out the first service.

Test the generator periodically.

This ensures you are familiar with the starting procedure and confirms the equipment is operating correctly.

For quiet emergency applications, explore our Silent Generators.

Portable Power Stations Do Not Need Engine Running-In

A Portable Power Station operates very differently from an engine-driven generator.

Because it uses rechargeable batteries rather than an internal combustion engine, there is no traditional engine running-in process.

There is no engine oil to change, spark plug to inspect or fuel system to maintain.

You should still follow the manufacturer's charging and battery-care instructions, but a portable power station can be an attractive option for users who want low-maintenance, quiet, emission-free portable electricity.

Common Running-In Mistakes

Some common mistakes to avoid include:

• Starting the generator without checking the oil

• Using old or incorrect fuel

• Immediately applying maximum load

• Running continuously at maximum output

• Ignoring the initial oil change

• Operating indoors

• Overloading electrical outlets

• Ignoring unusual noises or leaks

• Using incorrect engine oil

• Failing to record operating hours

Taking a little extra care during the first few hours can help avoid problems later.

New Generator Running-In Checklist

Before first use:

• Read the owner's manual

• Check engine oil

• Add fresh correct fuel

• Inspect for damage

• Check battery connections

• Position the generator safely outdoors

During initial running:

• Start without electrical load

• Allow the engine to stabilise

• Introduce loads gradually

• Avoid sustained maximum output

• Vary loads where appropriate

• Monitor oil level

• Check for leaks

• Listen for abnormal noises

After initial running:

• Complete the first oil change when specified

• Check filters

• Inspect fasteners

• Record engine hours

• Begin the standard maintenance schedule

Shop Generators for Trade, Home and Business Use

If you are choosing a new generator, selecting the right model for the application is just as important as running it in correctly.

Explore our generator ranges:

• Petrol Generators

• Diesel Generators

• Inverter Generators

• Silent Generators

• Open Frame Generators

• Three-Phase Generators

• Portable Power Stations

Whether you need portable power for tools, a quiet inverter generator for leisure use or a large diesel generator for business standby power, correct setup and maintenance are essential.

Final Thoughts

Running in a new generator correctly is a simple but important part of protecting your investment.

The exact procedure will always depend on the generator manufacturer and engine type, but the general principles are straightforward.

Use the correct oil and fresh fuel, start the generator without a heavy load, allow it to warm up, introduce electrical demand gradually and avoid sustained maximum loading during the initial operating period.

Most importantly, follow the manufacturer's first oil-change and servicing requirements.

Taking care of a generator during its first few hours of operation can help establish a strong foundation for dependable performance throughout its working life.