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How long does oil last in a generator?

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If you own a generator you want to be confident you can rely on it to provide power as and when you need it, such as during a power outage. So knowing how to maintain and protect your generator from damage is essential.

Oil plays a vital role in making sure a generator is running smoothly. Your owner’s manual should supply you with all the information you need to keep up general generator maintenance, including how to change oil, how to check your oil filter, and how to know when you require oil.

To know how long the oil will last in your generator, follow the interval outlined in your owner’s manual. As a general rule for portable units, it’s recommended you do a full oil change every 100 hours of use, although for generators with a small engine you may need to do this every 20-50 hours.

If your generator stops working, the oil levels are the first thing you should check.

What factors affect the need to change the oil?

Whether it’s a portable generator, petrol or diesel generator you’ll need to check the oil levels regularly to avoid the risk of low or no oil, which is hugely damaging for generators.

The length of time the oil lasts in a generator and if it needs regular oil changes, will depend on a few things:

  • The type of generator
  • Whether the generator is in light or heavy use
  • The location, temperature and environment of the generator

If you have a more modern generator, you’ll probably find it needs less oil changes. This is because they burn cleaner than older generators.

Having said that, with any new generator the manufacturer will recommend you do the first oil change after the first 8 hours of use as part of the break in process. This ensures any contaminates that may have gotten in the generator during manufacturing and shipping are cleared out.

The location of your generator also plays a role. If your generator is stored or located in an area with lots of dust or debris, you’ll need to change the oil more regularly to rid the oil of any contamination.

You also need to think about the temperature your generator will be operating in. In hot temperatures you’ll need a higher viscosity oil, compared to cold temperatures when you’ll need a lower viscosity oil.

What part does oil play in the functions of a generator?

Generators come in a variety of sizes and types, from small petrol generators to large diesel generators. They all have one thing in common, though: they need oil to function properly.

Oil lubricates the engine and prevents wear of a generator by reducing the friction between its components. It stops moving parts coming into direct contact, causing damage and preventing the generator from seizing up.

It also plays an important role in cooling the engine. Continuous running of a generator can cause it to get quite hot. The oil helps to dissipate this heat and keep the engine from overheating. Without oil, the generator would quickly overheat and fail.

It is essential you check the generator’s oil regularly to prevent the risk of damage to the engine and motor. Especially if your generator is in heavy use.

The oil change process and importance of

Changing the oil is all part of your generator maintenance. Over time oil can become contaminated with dirt and debris.

The oil change process is relatively simple, firstly make sure your generator is on a level surface. If the generator has been in use allow it to cool down for a bit before you change the oil to avoid the risk of burning yourself.

Hot oil is more fluid so if your generator hasn’t been running it’s worth running it for a couple of minutes to warm the oil slightly.

To start, locate and unplug the spark plug to prevent accidentally starting the engine. Unscrew the oil drain plug and drain old oil into a suitable container. Once drained re-screw the plug firmly. Next fill the engine with the oil type recommended in your owner’s manual.

If your generator has an oil filter replace this as well. It’s not essential every time but it does help prevent new oil running through dirty old filters.

Now you can reconnect your spark plug and start up your generator. Let it run for a few minutes to allow the new oil to filter through. Stop and check the oil level again to make sure it’s filled to the correct level, if not, repeat the above process.

Can oil sit in a generator for a period of time?

If you only use your generator for the occasional power outage, it may sit unused for a period of time. If you’re storing a generator it’s not recommended to leave fuel in the fuel tank unless you use a stabiliser. Fuel will degrade over time and can clog the air filter and fuel lines.

Oil does have a shelf life but it can be left in the generator while in storage, you may need to change the generator’s oil before using it again if it’s been sat for a long period of time as dust and debris may have contaminated the oil.

It’s recommended you start your generator once a month to maintain it and ensure you can rely on it in times of sudden power outages.


How long oil lasts in a generator is relevant to the model of generator, the environment it’s used in, and the level of its use.

Manufacturer guidelines recommend you change oil after the first 8 hours of use for a newly bought generator, and roughly every 100 running hours from there on depending on the size, make, and model.

To ensure you have power when you need it, be sure to check your generator’s oil regularly and consult the owner’s manual for guidance on your specific generator.

If you would like further advice on looking after your generator, contact the team at Solent Power, we would be happy to help.

Paul Phelps Solar Power Owner
Paul Phelps
Paul is the MD of Solent Power and specialises in emergency power solutions, helping to protect your facilities from power loss. Get in touch with us today to discuss the different power brands that we can offer and how they can suit your needs.
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