7 Reasons Why Onan Generator Starts Then Shuts Down

Generators are a common sight in many households, especially those who live in areas with frequent power outages. Among the top generator brands in the market is Onan generator. This reliable generator comes in handy when you require a temporary power source. The question one may ask is why onan generator starts then shuts down.

This is common if the generator is not properly maintained and serviced. This blog post will discuss some of the reasons why your Onan generator starts then shuts down and what you need to do if this happens.

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Reasons Why Onan Generator Starts Then Shuts Down

There are several possible reasons why your Onan generator starts then shuts down. Some of these reasons include:

1. Low oil level

Onan generators are designed to shut down if the oil level goes below a specific limit. If the oil level is too low, it can cause damage to internal engine parts and lead to a malfunction. One way of ensuring that your Onan generator will not shut down because of low oil level is to check the oil regularly and replace it as needed. If the generator shuts down because of low oil, add oil and restart it.

2. Low fuel level

Onan generators are designed to shut down if the fuel tank is running low. In most cases, an Onan generator will start and shut down almost immediately if the fuel level is below the quarter tank mark.  The generator will only start with the fuel in the carburetor and stop once the little fuel is used up.

3. Stale fuel

Onan generators run on gasoline. Over time, exposure to air and extreme temperatures can cause the gas to turn bad. The gas needs to be fresh and of high quality for the generator to start.

4. A clogged carburetor

A generator carburetor ensures that the right amount of air and fuel are mixed for the generator to run smoothly. However, when the carburetor clogs, the mixing of fuel and air is limited, causing the generator to start and stop. The carburetor’s clogging results from leaving fuel in the generator during a long storage period. When this fuel stays for an extended period, it evaporates and some, of the fuel elements, evaporate leaving a thick and stickier residue that clogs the carburetor. Ensure to drain the carburetor whenever you store the generator.

5. Clogged air filter

The air filter ensures that the generator has enough air supply to run smoothly.  If particles, including dust, clog the air filter, it may not draw enough air. Because of this, the generator will not operate correctly. Even if the generator starts, it will not for long hours.

6. Poor maintenance services

Your Onan generator needs to be maintained to run smoothly. Failure to perform regular maintenance and service can cause your generator to start and shut down.

7. When the generator overheats

Onan generators will stop running when they are hot to prevent damage to the internal engine parts. The generator can overheat when it is overloaded and when the airflow to the engine is restricted. Also, check whether the cooling fins are clogged by dirt.


When your Onan generator starts and shuts down, you need to troubleshoot it to determine what is causing the problem.


How to Troubleshoot an Onan Generator That Starts Then Shuts Down

Here are easy tips for troubleshooting your Onan generator;

  • Start by checking some basics like the circuit breakers and if the generator is plugged in.

Reset the circuit breakers, and if the generator starts, the issue is with the circuit.

  • Check the choke setting.

The choke is a knob that controls the amount of air intake for optimal combustion in the engine. If set too high, it can cause an engine to stall and shut down. If the choke is not adjusted correctly, the generator will start and shut down after a few seconds.

  • Check the fuel pump and the carburetor.

If you suspect that there is a problem with the pump, remove and clean it to make sure that no dirt or debris gets into it. You can test it by checking if it can produce suction and pressure. On the carburetor, check out for any dirt or debris that might be clogging it, causing the engine to shut down.

  • If you have a multi-meter, use it to check on the voltage output of the generator.

Take note of the amperage of the generator. If you notice that the amperage is lower than normal, low oil or fuel level can be the leading causes.

  • Check out for worn-out spark plugs and replace them if necessary.

Worn-out spark plugs can cause the engine to shut down because of a lack of spark.


Caution: If you are not sure whether you can troubleshoot a generator by yourself or not, consult a qualified generator technician to do the troubleshooting for you. Generators can be dangerous when mishandled.


Frequently Asked Questions

1. How much does it cost to rebuild an Onan generator?

Rebuilding an average Onan twin-cylinder will cost you at least $2000 (including labor and spare parts). Depending on the nature of your Onan generator, you may be charged higher or lower than the $2000 cost. The cost may also vary depending on the availability of the parts.

2. Can you run a RV generator while driving?

Yes, it is technically possible to run an RV generator while driving. The generator can run on the gasoline from the RV tank, but the generator will shut down when the fuel level in the RV fuel tank drops below the quarter tank mark.  Even so, it is not advisable to run the generator while driving.

3. How much does it cost to replace an RV generator?

The cost of replacing an RV generator varies depending on the generator’s brand. Contact your local dealer for a quotation or more information about replacement costs.

4. Can a generator be rebuilt?

Yes, you can rebuild most generator models. However, do not attempt to rebuild the generator by yourself unless you are a qualified generator technician.

5. How much does it cost to rebuild a generator?

Why Onan Generator Starts Then Shuts DownThe average cost of rebuilding a generator ranges from $161 to $367. The prices differ depending on whether the generator is portable or a standby model.

6. Are generators worth fixing?

Yes, especially if the generator is still under warranty; it may be best to have the parts replaced by an authorized dealer. If you bought a used generator, it might be worth having it rebuilt instead of buying a new one.

7. How do you change a generator brush?

In most cases, the generator brushes are located in a compartment on the right side of the generator. Open the cover of your generator and disconnect the negative-positive connections from the holder, and remove the brushes from their casing using a screwdriver. Then, you need to remove the springs and put new brushes into the casing using a small brush or toothbrush. Finally, you need to attach the negative-positive connections and cover.

More information on the video

8. How do I remove a pulley from a generator?

First, disconnect the positive and negative wires of the battery to prevent it from short-circuiting. Then, remove the bolts holding your generator in place and pull out the rotor carefully to avoid damaging it or yourself. You can also block the blades to prevent injuries. To reinstall, put in the rotor and bolt it carefully, not over-tightening them. Then, attach your battery’s negative and positive wires to ensure that it turns on.

9. Should you poop in your RV?

RV toilets can take care of human waste, including poop. If you have plenty of clean water for flushing the loo, you can poop in the RV without experiencing smells or clogs.

10. Is it okay to run RV generator all night?

Yes. However, you should ensure that all doors and windows of the RV are closed. The generator should be placed outside the RV and in the open air. Also, check if your generator has enough fuel and oil to last it overnight.

11. How do I keep my RV fridge cold while driving?

Why Onan Generator Starts Then Shuts Down

To help your fridge stay cold during the drive, get it as cold as you can before leaving for your journey. Regulate the thermostat to the lowest setting and fill any empty spaces with bags of ice, freezer packs, or ice-cold beverages.

12. Can you run RV generator while plugged into shore power?

You can use an RV generator while the RV is plugged into shore power if you have a transfer switch. However, the shore power will not connect. RVs with an in-built generator usually have an automatic transfer switch which means you cannot have both generator power and shore power simultaneously.

13. Are you required to wear a seatbelt in an RV?

Yes, it is required by law to wear a seatbelt in an RV, and you should do so whenever you are driving. Make sure that the driver and all passengers wear their seatbelts.

14. Why won’t my RV generator stay on?

Why Onan Generator Starts Then Shuts DownYour RV generator may not stay on because of low oil or fuel level. Other reasons for your generator not staying on include:

  • A clogged air filter
  • Using low-quality fuel
  • The generator is overheating

If you realize your generator keeps shutting down yet the air filter is clean, you are using quality fuel, and the unit has enough oil, contact your brand’s service dealer near you.

15. Why does my generator keep cutting off?

There are several reasons why your Onan Generator may be cutting off. If the engine is overheating, it may be due to low oil or lack of fuel in the generator. Another possible cause is that the generator start button has been pressed too many times. You can also check your manual for troubleshooting information related to your generator cutting off.

16. How do I reset my Onan generator?

After fixing the problem on your Onan generator, it is necessary to reset it to clear the error code. Here are easy steps of resetting an Onan generator:

Step#1: Find the primer button located below the gas tank of your Onan generator.

Step#2: Long press the button (primer) for about 30 seconds.

Step#3: Release the button and power on the generator.

Step#4: Let the generator run for about fifteen minutes; the error code should have cleared by the end of the fifteen minutes. If the error code does not clear, contact an authorized Onan service dealer near you.

17. How do I find my Onan generator error code?

Remove the generator cover, access the manual on/off switch, hit the primer button thrice within five seconds, and monitor the blinking. The indicator on the switch will blink thrice, then pause, hit the button once more, and count the number of blinks you’ll get. The consecutive number of blinks before a pause represents the first number of the error code.  The next number of the error code will be the number of blinks the light indicator displays.


For instance, if you get the first three blinks a pause, then six blinks, the error code will be 36. You now have the error code. To see what it means, visit the Onan official website and look at what error code 36 means.

18. How long do Onan generators last?

Onan generators can last anywhere from five to twenty years, depending on how well you maintain them and the conditions they are exposed to. Onan generator can offer you 30,000 hours of continuous operations in terms of running hours. To maintain optimal performance, they require regular oil changes, clean and quality fuel, filter replacements, and carburetor cleaning.

19. How do you jumpstart an Onan generator?

You will need quality jumper cables to do this: Start by connecting the negative (black) clamp of the jumper cable to the negative post of your vehicle’s battery. Take the other end (negative clamp) of the jumper cable and set it to any unpainted metal frame part of the generator. Proceed by connecting the positive clamp (red) of the jumper cable to the positive post of your vehicle’s battery, then connect the other positive (red) end of the jumper cable to the positive post of your generator’s battery.


While the connection is set, start your vehicle and allow it to run for about five minutes. Start your Onan generator after five minutes, and it should be ready to pick. Immediately after the generator starts, disconnect the cables. Prevent the positive and negative clamps from coming into contact when the other end is hooked to the battery.


Caution: When jump-starting your Onan generator, the negative jaws of your jumper cables should only be connected to the metallic surface of your generator’s frame. Do not smoke cigars near the battery or the generator.

20. Are Onan generators good?

Cummins Onan is one of the leading manufacturers of the best RV generators. Their generator brands are reliable, easy to maintain, lightweight, low fuel consumption, and easy to install. The models are also tough and are long-lasting. The lifespan of an Onan RV generator can outdo the lifespan of the RV. They do not require frequent maintenance and provide the owner with maximum performance, lasting for decades to come.

Final Word

Onan generators are among the best generator brands in the market. However, just like any other mechanical device, generators can malfunction. Their malfunctioning includes shutting down after the generator has been started. Shutting down of an Onan generator after starting could be a result of several factors including, low oil levels, clogged carburetor, and using low quality or stale fuel. Even though there are such factors, knowing the exact cause of the generator shutting down can be a problem. Luckily, you can learn to troubleshoot your Onan generator and point out the problem. As a precaution, contact an authorized Onan service dealer near you if the shutting down problem persists.




About Steve Stuart

Steve Stuart is an electrical engineer who developed interest on generators during his school years. After school, he became a generator enthusiast. This is after encountering power supply problems at the area of residence where he lived. Power would be on and off and so food would go bad and the room heater would go off especially during winter. After trying the different generator brands for several years, Steve now provides information on the available brands and products in the market today. Based on his experience, he gives the do’s and the don’ts when it comes to generator use.

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