Onan 4000 Generator Oil Type (Troubleshooting)

The Onan 4000 generator, is renowned for its reliable performance and longevity. It is a common choice for RV enthusiasts, homeowners, and businesses alike. However, like all mechanical equipment, its longevity and optimal performance are contingent upon regular maintenance, particularly concerning oil maintenance.

Onan 4000 Generator Oil Type

Oil plays a vital role in the smooth operation of a generator. It serves as a lubricant, reducing friction among the moving parts, which prevents overheating and wear. Furthermore, oil aids in maintaining a clean engine by suspending contaminants and directing them to the oil filter.

Failing to change the oil at regular intervals can lead to damaging consequences such as engine wear, overheating, and eventually, engine failure.

Right Oil for Onan 4000 Generator

Generators can use a variety of oil types, including conventional, synthetic, and blended oil. For the Onan 4000 generator, it is recommended to use high-quality oil, SAE 15W-40, in most temperature ranges. However, depending on the ambient temperature, you may need a different viscosity.

For example, in temperatures below 32°F, SAE 5W-30 is advisable. Always refer to the user’s manual for the most accurate information.

Onan 4000 Generator’s Oil Capacity

Knowing the oil capacity of your Onan 4000 generator is essential. The correct amount of oil ensures optimal operation while avoiding damage from overfilling or underfilling. The Onan 4000 generator typically has an oil capacity of around 1.6 quarts.

Overfilling can cause the oil to foam, leading to inadequate lubrication, while underfilling might not provide sufficient lubrication for all moving parts.

onan 4000 generator oil change
@Dave’s RV Life

Steps to Change Oil in Onan 4000 Generator

Regular oil changes are crucial to the health of your generator. The frequency of oil changes can depend on usage and operating conditions, but a general rule of thumb is to change the oil every 100 hours of operation or at least once per year.

For the oil change, you’ll need a wrench, oil pan, funnel, new oil filter, and the correct amount of oil. The process is relatively simple:

  1. Warm up the generator for a few minutes, then turn it off. This makes the oil flow smoothly.
  2. Place your oil pan under the drain plug and remove the pin with a wrench, allowing the oil to drain out.
  3. After the oil is drained, remove the old oil filter and replace it with a new one.
  4. Replace the drain plug and pour in the new oil through the oil fill opening using a funnel.
  5. After filling, check the oil level using the dipstick to ensure it’s within the marked range.

Safety Measures While Changing Oil

Safety should be your primary concern when changing the oil. Ensure the generator is turned off and cooled down to avoid burns. Wear gloves and eye protection to prevent any oil splashes. Remember to properly dispose of the used oil and oil filter at a recycling center as it is hazardous to the environment.

Troubleshooting Common Oil-related Issues

Despite diligent maintenance, you may encounter some oil-related issues with your Onan 4000 generator.

Oil leakage is one such problem that may be due to a loose drain plug or a damaged oil filter. In such cases, tightening the plug or replacing the filter should rectify the issue.

If the generator is producing excessive smoke, it might be due to overfilling of oil. Correcting the oil level should solve the problem.

For more complex issues, such as unusually high oil consumption, you may need to consult with a professional.

onan 4000 generator oil filter

The oil filter for the Onan 4000 generator plays a crucial role in maintaining the quality of the engine oil. It filters out dirt, debris, and contaminants to keep the oil clean, which helps protect the engine from premature wear.

The specific oil filter you need can depend on the exact model of your Onan 4000 generator.

However, one commonly used oil filter for the Onan 4000 generator series is the Onan 122-0836. This oil filter model is designed to provide a high filtration efficiency, maintain high oil flow rates, and offer a long service life.

It’s important to note that you should always refer to your generator’s owner manual or consult with an Onan service center to ensure you have the correct oil filter for your specific generator model.

When changing the oil filter, you’ll want to follow these steps:

  1. Place an oil pan beneath the filter to catch any oil that spills out when you remove it.
  2. Use a filter wrench to loosen and remove the old filter.
  3. Before installing the new filter, apply a small amount of clean oil to the gasket on the top of the filter. This will help create a better seal and make it easier to remove the filter during your next oil change.
  4. Install the new filter by hand, turning it clockwise until the gasket contacts the filter adapter, then tighten it an additional 1/2 to 3/4 turns.

Remember, safety first. Always ensure the generator is cool to avoid burns and always dispose of used oil and filters at a recycling center.

onan 4000 generator oil change kit

An oil change kit for your Onan 4000 generator will typically include everything you need to perform a routine oil change. While the specific components may vary depending on the kit, you can generally expect to find the following items:

  1. Engine Oil: The quantity of engine oil included should be sufficient for one oil change. As previously mentioned, SAE 15W-40 is commonly recommended for the Onan 4000 generator in most temperature ranges, but you should always check your generator’s manual to confirm the correct type and quantity of oil required.
  2. Oil Filter: This is necessary for removing contaminants from the oil, ensuring that it remains clean and effective in lubricating your generator’s engine. An example of an oil filter for the Onan 4000 series is the Onan 122-0836.
  3. Funnel: A funnel is typically included to help you avoid spills when adding new oil to your generator.
  4. Disposable gloves: These help protect your hands during the oil change process.
  5. Instruction manual: This will guide you through the oil change process step-by-step.

One such kit that fits the description above is the Cummins Onan Green Label Parts 152-0438 Oil Change Kit for HGJAA, HGJAB, and HGJAC. However, always ensure that the kit is compatible with your specific generator model before purchasing.

Remember, while these kits can make the oil change process simpler and more convenient, always adhere to safety precautions when performing maintenance on your generator. And, don’t forget to properly dispose of your used oil and oil filter at a local recycling center.

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In conclusion, oil maintenance is an essential part of owning an Onan 4000 generator. Regular oil changes, using the right oil, and maintaining the correct oil level can significantly extend the life of your generator and ensure its optimal performance. With the right approach, most oil-related issues can be easily prevented or solved, ensuring your generator remains reliable for years to come.


Rayan is an engineer, lives in a farmhouse. He has a passion for electronics and alternative energy. He loves to share his thoughts with other people. That is why he started the blog.

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