6 Top Reasons Why Onan Generator Dies Under Load And Their Solutions 

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Just like any other generator brand you can think of, Onan generators can also malfunction and cause you trouble. One of the common problems that Onan generator owners face is when the generator starts and then dies under load. 

This means that the generator runs fine when it is idle but shuts off when you plug in something, turn on an appliance that draws power from it, or it runs for a few minutes and shuts down before you plug in any of your appliance. This can be very frustrating and inconvenient, especially when you need power for your essential needs.

In cases like this, if your generator is still new, you should take it back to the dealer if it’s still on warranty terms. But if it isn’t, then you should try to know what causes the problems and how you can fix them.

Fortunately, you don’t need to worry much about the causes and how you can fix them. In this blog post, we will explain why your Onan generator dies under load and how you can fix it. 

Possible Causes and Solutions for Onan Generator Dying Under Load

Onan Generator Dies Under Load
This is Onan Microquiet 4000 generator under a recreational Vehicle.

Several factors can cause your Onan generator to die under load. Some of them are easy to fix, while others may require professional help. Here are some of the most common causes and solutions for this problem:

Causes EffectsSolutions
Low fuel levelInsufficient fuel enters the carburetor. Can cause the generator to sputter, stall, run rich, and then shut down. Fill up the fuel tank, and check the fuel gauge.
Clogged fuel filterLack of free flow of fuel from the tank to the carburetor fuel is dirty in the fuel filter and the fuel line.Check, clean, or replace the fuel filter, and check the fuel line.
Dirty or Clogged CarburetorPoor fuel-air ratioClean or service the carburetor by cleaning the jets, draining old fuel, and refilling fresh fuel in the generator tank.
Faulty Spark PlugIgnition failure is due to the spark plug not producing enough spark to ignite the engine.Clean or replace the spark plug, check the ignition switch, check the spark plug wire, and check the ignition coil. 
Low Oil LevelLack of oil, overheating.Check and fill up the oil crankcase if there is no oil; replace the oil filter if it’s clogged; and check the oil pressure sensor.
Bad Gas CapVacuum in the fuel tank prevents the free flow of fuel.Tighten, repair, or replace the gas cap, and check the vent hose or vent hose.

Now, let’s explain further about the table above. 

1: Low fuel level

One of the simplest reasons why your Onan generator dies under load is that it does not have enough fuel to run. 

This can happen if you forget to check or refill your fuel tank when the fuel is low or if your fuel gauge is faulty. 

To fix this, you need to fill up your fuel tank with fresh and clean fuel. You should also check your fuel gauge and make sure it is working properly. If not, you may need to replace it or have it calibrated.

You can also read what happens then Onan Generator Only Runs When Holding the Start Button.

2: Clogged fuel filter

Another reason why your Onan generator dies under load is that the fuel filter is clogged or dirty. The fuel filter is a device that filters out any dirt, debris, or water from the fuel before it reaches the engine. If the fuel filter is clogged, it will restrict the flow of fuel to the engine and cause it to starve and shut off. 

To fix this, you need to replace the fuel filter with a new one. You should also check the fuel line and make sure it is not kinked, pinched, or damaged.

You can read further on How to Clean Generator Fuel Filter in 8 Simple Ways if the explanation above isn’t helpful enough.

3: Dirty carburetor

A dirty carburetor is another common cause of Onan generators dying under load. The carburetor is a device that mixes air and fuel in the right proportion for the engine to run. 

If the carburetor is dirty, it will affect the fuel-to-air ratio and cause the engine to run poorly or stall. This can happen if you use old or contaminated fuel or if you leave your generator unused for a long time. 

To fix this, you need to clean the carburetor with a carburetor cleaner or compressed air. You should also drain the old fuel from the tank and the carburetor and refill them with fresh, clean fuel.

4: Faulty spark plug

A faulty spark plug is another possible cause of the Onan generator dying under load. The spark plug is a device that creates a spark to ignite the fuel-air mixture in the engine. If the spark plug is worn out, dirty, or damaged, it will affect the ignition and cause the engine to misfire or stall, resulting in your generator shutting down under load. 

To fix this, you need to replace the spark plug with a new one. You should also check the spark plug wire and make sure it is not loose, corroded, or broken. If you have checked the spark plug and the spark plug wire, there’s no fault. You should also check the ignition switch and the ignition coil to see if they are loose or broken. 

5: Low oil level

A low oil level is another reason why your Onan generator dies under load. The oil is a lubricant that reduces friction and heat in the engine. If the oil level is low, it will cause the engine to overheat and shut off. This can happen if you forget to check or change your oil, if the oil sensor is faulty, or if your oil filter is clogged or dirty. 

To fix this, you need to fill up your oil tank with the right type and amount of oil. You should also replace your oil filter with a new one. You should also check your oil pressure sensor and make sure it is working properly. If not, you may need to replace it or have it calibrated.

6: Bad gas cap 

Lastly, a bad gas cap is another factor that can cause your Onan generator to die under load. The gas cap is a device that seals the fuel tank and prevents any air or moisture from entering or escaping. 

If the gas cap is bad, it will create a vacuum in the fuel tank and prevent the fuel from flowing to the engine. This can happen if the gas cap is loose, cracked, or missing. 

Other components around the gas gap that can also cause this are the fuel lines. If the vent hose is broken or clogged, it can also stop fuel from flowing, resulting in your generator shutting down under load. 

To fix this, you need to tighten, repair, or replace the gas cap with a new one. You should also check the vent hose and make sure it is not clogged, kinked, or damaged.

How to Maintain Your Onan Generator and Prevent It from Dying Under Load

To prevent your Onan generator from dying under load, you need to maintain it properly and regularly. Here are some tips and steps to help you keep your generator in good condition and avoid any problems:

1. Read the owner’s manual.

The owner’s manual is your best source of information and guidance on how to use and care for your Onan generator. It contains important safety instructions, specifications, troubleshooting tips, and maintenance schedules. You should always read the manual carefully and follow its recommendations when your generator is faulty. If you don’t have your Onan generator manual with you, you can comment on your engine model number before so we can help you send a PDF version of it. 

2. Check the oil and fuel levels. 

Next, you should always check the oil and fuel levels before every use and after every 8 hours of operation. And also, change the oil and fuel filters according to the manufacturer’s instructions. 

Many Onan generator owners mistake using the wrong oil for their generators, but you shouldn’t do so. You should ensure that you use the right type and quality of oil and fuel for your generator. You can check your manual for the recommended one.

Additionally, you should also avoid using old or contaminated oil and fuel, as they can damage your engine and cause it to die under load.

3. Clean the air filter.

Apart from oil changes, you should always clean the air filter every 50 hours of operation, or more often if you operate your generator in dusty or dirty conditions. 

To achieve this, you should use a soft brush or compressed air to remove any dirt or debris from the air filter. But if the filter is beyond cleaning, you should replace it. 

4. Clean the spark arrestor.

You should clean the spark arrestor every 100 hours of operation, or more often if you operate your generator in dry or wooded areas. The spark arrestor is a device that prevents sparks from escaping the exhaust and causing a fire. You should use a wire brush or a scraper to remove any carbon deposits from the spark arrestor. You should also replace the spark arrestor if it is damaged or corroded.

5. Inspect the belts and hoses.

If your Onan generator is using belts and hoses, you should inspect the belts and hoses every 250 hours of operation or once a year

When inspecting, you should look out for any signs of wear, cracks, leaks, or looseness. You should also adjust the belt tension if needed.

Additionally, if the belts and hoses are getting damaged or are deteriorating, you should replace them immediately to avoid further damage.

6. Test the battery.

You should test the battery every 500 hours of operation or once a year. While testing, you should use a voltmeter or a hydrometer to measure the battery voltage and specific gravity. 

You should also check the battery terminals and cables for any corrosion or damage. You should clean and tighten the battery connections if needed. You should replace the battery if it is weak or dead.

7. Store your generator properly.

Lastly, you should store your generator in a cool, dry, and well-ventilated place when not in use. You should also cover your generator with a protective cover to prevent dust, moisture, and insects from entering it. 

You should also drain the fuel from the tank and the carburetor if you plan to store your generator for more than a month. You should also run your generator for a few minutes every month to keep the engine lubricated and prevent any problems.

These are some of the basic maintenance tips and steps that you can follow to keep your Onan generator in good shape and prevent it from dying under load. However, if you encounter any issues that you cannot fix by yourself, you should contact a qualified service technician or an authorized dealer for assistance

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