Onan Marquis 5000 Generator Guide (Oil Type, Parts, Manual)

If you get a chance to buy an Onan generator at a fairly cheap price, do not ignore it. These are good machines and they hold their value. That is if you take care of them and do proper maintenance when needed.

While not perfect, these generators seem to be some of the most sought-after models today. They seem to be well built and one company won’t list its used sale price. That means they hold their value for a long time. They are hard to find these days.

To learn more about this generator model, just continue to read our article. It explores the topic so you have the best information possible. That way you can make a very informed decision when it comes time for you to buy a new or used Onan generator.

Onan Marquis 5000 Oil Type


According to the manual, you have a little freedom when it comes to the brand and viscosity of the oil. There are many good brands of oil out there and you can stick to your favorite if you want to.

What the manual says about what engine oil to use is this- “Use oil with the API designation class SE or SF then use the following oil when the temperatures get to certain levels.

Above 60 degrees F use SAE 30 and below 60 degrees F use SAE 20. Make sure to check the oil after the generator has run and is still warm. When you are checking the oil, make sure the generator is level.

That way you will not get a bad reading. Be careful about spilling hot oil on yourself. Like hot water, hot oil can burn your skin. Then when the oil has drained, make sure to put the oil drain plug back in before you start filling the oil tank with oil.

You would be surprised at how many people have done the opposite at least once in their lifetime.

How Much Fuel Does an Onan 5000 Generator use?

The amount of fuel that you will go through on an average day will depend a lot on the type of fuel your Marquis 5000 uses. The following information is generic and should give you a good idea of the amount of fuel you need on hand.

For the gas-powered models, you are looking at burning anywhere between 1/2 to 1 gallon of fuel. Your usage will depend on the load and how hard the generator has to work.

For the propane models, you are looking at using a bit more than that. On average your generator may use between 1 to 1 1/2 gallons of propane every hour. Your usage will differ from other RVers so you may pay more or less for your fuel than they would.

These are only average figures and your usage may depend on how well you maintain this device. A fouled spark plug, clogged filters, low oil, and so on will help your generator use more fuel than you expected to use.

Keep a record of your usage so you have an idea of how much fuel you go through when the generator is in use.

Download The Onan Marquis 5000 Generator Manual

Our go-to download manual website has made some changes to its web pages. While you can still read it, copying and pasting seems to be a thing of the past with them.

That is understandable as they are in the business of selling these manuals. You will have to download the entire manual for the price they charge. To see it and do that, just click here.

The best place to go to get your manual, and it is free, would be the Cummins website. They have a manual page for generators and you can access it here. If you do not see the manual for this particular generator model, contact the company and see what they say.

Or you can try any one of the Onan dealers to get a hard copy or a website to download one. We say that because both our go-to website and Cummins’ website are the majority of results for this topic.

A good internet search should turn up more websites that offer this manual for a download. They may not all be free like the Cummins’ offer but at least you will have the manual.

Onan Marquis 5000 Generator Wiring Diagram


We checked the owner’s manual and there are some great diagrams within its pages. However, there was no wiring diagram to be found. But we did find several websites that had wiring diagrams labeled as for the 5000 generators.

Whether they truly are or not remains to be seen. Here is one example of what you can find on the internet:

We have found other diagrams and one website is found at this link. There are several diagrams on that website that may be of some service to you. You may find one in a service manual and that may be found on the Cummins’ website.

You may have to contact the company to see what they say. There are manufacturers who do not like issuing wiring diagrams due to liability issues. Also, they do not want amateurs working on their electronics.

Those two may be the reason why Cummins may not issue a wiring diagram. It does not hurt to ask though. If you are good, you can always make your own. Just make sure to store it in a safe place so you do not have to go through this again.

Finding Onan Marquis 5000 Generator Parts

You can use the Cummins website link for manuals to get to their parts section. There is a separate page for parts for Onan generators and you can find that page at this link.

Which one you use will be up to you. Of course, you can use their dealer locator tool and find a dealer that is near you. That may be more convenient than shopping online.

Amazon has been seen selling a motor starter for the 5000 generator but we did not see many more parts on that marketplace. That part seems to be currently unavailable at this time.

But if you do not like Amazon, there are many other Onan parts and repair outlets that pop up in a basic internet search. The key would be to find one near you and get a quote before you head into the store.

You can look in the classified ads to see if there is a repair shop near you. They should have parts for sale. Or check your local listings to see what is available in your area.

Since Cummins is still making Onan generators, parts should be easy to locate no matter where you might be.

Onan Marquis 5000 Oil Filter

This may be one time when shopping at Amazon is not going to get you the cheaper price. The model number for this oil filter is 122-0645 and the part number is 482010.

At Amazon, the cost is just over $13, and at RV parts country the oil filter sells for about $1.07 less. In the manual, there are no directions on how to change the oil filter but it stands to reason it will be similar to changing the oil on other devices.

Now that you have the part number and the model number, you should be able to go into any supply outlet and find a compatible option if you do not want to pay the price for the Onan branded option.

There should be some compatible oil filters at an even cheaper price available. Many different brands make a wide variety of oil filters. You should be able to save a few bucks by using this route.

Check the different RV parts stores to see what is available and if they have a good alternative to the Onan filter.

Onan 5000 RV Generator Fuel Pump


These should be the part numbers from both Onan and Cummins- Onan 149-2331-02, Cummins A047N923 A029F891. The compatible fuel pump parts numbers are- E11009 A047N923 A029F891 149233102 149-2331-02 149-2331-03 149-2331.

If you are having trouble with the fuel pump, there could be a loose wire that connects the pump to the starting relay. Or the wire may be damaged or corroded.

Other problems that may occur may be a blown fuse or the pump’s wire screen being clogged. All of these are easy fixes and can be done in no time. Some owners are saying what they did when they had a fuel pump problem, the pump would start and then the generator would shut down after 10 to 15 minutes.

One owner put a bigger and new pump on the outside of the generator and then hardwired a new hot wire from the old pump to the new one. He claims he has not had a problem with the fuel pump since.

Another owner changed all the following parts but did not have success till he changed the old fuel pump for a newer one:

- changed plugs

- changed oil and filter

- changed the air filter

- field flashing to return residual magnetism

- changed the fuel filter

- changed the fuel pump

Onan Marquis 5000 Voltage Regulator

To find this part, you will have to remove the cover of the generator. The voltage regulator is located at the bottom of the device just inside the side of the generator you screw the cover into.

The regulator is under the circuit breakers and enclosed in an aluminum box. It is very hard to miss it. To replace it, you should unhook the regulator harness and then unscrew the aluminum box.

The harness is a 12-pin connector and 2 screws hold the aluminum box in place. The problem with the screws is that the top one is easy and should be unscrewed last.

The location of the other screw is underneath the box and to get to it, you have to go through one of the holes in the side of the lip of the bottom tray. Unfortunately, not every generator has that hole in the lip of the bottom tray.

The model number for when you are replacing it with a new one is 56-826 and this seems to be the standard voltage regulator for the Marquis series of generators.

If you do not have that hole in the lip of the tray to access the bottom screw, use a ratchet with the proper screwdriver head to get it off. Also, undo the bottom screw first to save you a lot of trouble and frustration.

Onan Marquis 5000 Troubleshooting

It is said that you should perform maintenance on the generator about every 150 hours of operation. You can do it in less time if you want but do not go too far past that upper limit.

When it comes to the generator shutting off or not starting, make sure to check the fuel level first. The device could be out of fuel and you forgot to refill it. If you are camping in very hot climates, a vapor lock is a real possibility.

If you have a propane generator then the cold weather may contribute to the lack of starting and running power. Don’t forget to check the fuel line for possible blockages.

If your generator starts and stops, it may have nothing to do with the fuel system. Many of this company’s generators have a low oil shut-off switch. The generator will shut off when the oil level gets too low. So check that tank to see if you need to add any oil.

Other things you can do to help your generator run smoothly are to check and possibly change the spark plug, run a carb cleaner through the system, check the fuel filter, then the voltage regulator slip rings, as well as the circuit breakers.

Replace any part that is damaged, clogged, or wearing out. These are all checks to do when the generator starts but does not continue to run.

Onan Marquis 5000 Won't Start


Besides a fuel system problem, the source for this issue may be electrical. The first step would be to test the coil to see if 12-volt power is reaching the positive terminal. This is done while cranking the engine.

If you do have that power, it is time to use an ohm meter and test the coil. Attach the leads to each of the small terminals on the coil after removing all the wires.

You should get a reading between 3 to 5 ohms. Next, attach the leads to the spark plug terminals. Your meter should read between 14,000 to 30,000 ohms. If you do not get either of these levels then you need to replace the coil

If the coil is good or it won’t start when you replace the bad unit, then you move on to the ignition module. Here are the instructions to test that part:

Disconnect the spark plug wires. Disconnect the red and black ignition module wires from the terminals of the coil. Run a 12V jumper to the red wire. Set your meter to VDC and connect the negative lead to good ground. Connect the positive lead to the black wire coming from the ignition module. Using a 3/8" Allen wrench in the rotor through bolt located in the center of the right-hand side of the set, slowly turn the engine counter clockwise as viewed from the right end. The meter should read 12V for 1/2 revolution and drop to about 1V for the other half revolution. Turn the motor through at least 3 full revolutions…

If the voltage does not do what it is supposed to, you are either going to have a bad ignition module and/or a broken ignition rotor.” (source)

Finding an Onan Marquis 5000 For Sale

There are a variety of locations that sell one of these generators. There is not a lot of supply so they may be expensive even used. The classified ads would be your best option in your local area.

Then you can try the different RV discussion forums as you never know when someone upgrades to a more recent Onan generator model and wants to get rid of their older 5000 model.

Then you can try eBay to see if anyone is selling one on that marketplace. There are a few good options like RV parts outlets as well.

Some Additional Words

The Onan 5000 generator seems to be a very popular model to own. There are not that many for sale at this time but more may come up in the near future. These models seem to be well-built and handle your electrical needs like a pro.

If you do regular maintenance on them they should last you a very long time. Check with Cummins to see if you can get a service manual so you can do your own repairs once the warranty has expired.

Leave a Comment: