Onan 2500 LP Generator Troubleshooting, Manual, Oil Change

If it has a motor and moving parts, then you can expect products to break down eventually. This event is usually the result of poor maintenance, user errors, or inferior parts installed. Thankfully what breaks down can be rebuilt and fixed.

Oil changes are measured in ours. The first one comes after 20 hours of initial use. This lubrication change helps rid the generator of any metal shavings that may still be inside the device. After that initial oil change, you should do it every 150 hours.

To learn more about troubleshooting the Onan 2500 LP generator, just continue to read our article. It has the information you want to know about so you can get your generator up and running without too much trouble.

Onan 2500 LP Generator Troubleshooting


One of the best troubleshooting tips that can be given here is that you should run your generator at least 2 hours every month. This action will help remove any moisture inside the engine, etc., and make sure you have a 50% load on it while doing this preventive maintenance step.

Also, this action will help keep your generator lubricated which makes starting a lot easier, provides reliable operation, and helps extend the life of the generator.

Two other troubleshooting steps will be to check your air filter and air intake hose. If your generator is not working or not working normally this situation could be a result of a clog in either of those parts.

The sign that these parts are causing the trouble is when your generator operation is rough or uneven. Don’t forget to check the fuel as well. Contaminated fuel will create the same problem or even have your generator shut down.

If your Onan 2500 LP generator does shut down, check your oil level. The company did install a low oil sensor and it is equipped with the power to shut off the device when there is little to no oil left inside.

All you have to do here is refill the oil tank and you should be okay. The oil capacity ranges between 0.6 to 1 quart but check your manual to see what your specific model needs.

Next, check your spark plug. If you are having trouble starting the generator, it could be that the spark plug got fouled or burned out. Check the plug and change it if you see some burned marks, damage or it is just a little too old.

Section 3 page 5 of the owner’s manual has more troubleshooting information. Just be careful when you work on your generator. It does get hot and you can get burnt if you are not careful.

Onan 2500 Propane Generator Won't Start


There are several sources for this problem. One is that the fuel level is too low. If the fuel in the tank is below the minimum level set by Onan, the device will not start.

Then as stated earlier, if the oil sensor detects low oil, then it will keep the generator from starting. In both cases make sure to have both fuel and oil on hand to resolve the problem.

Another source for this problem will be a spark plug with carbon deposits on it. If you have filled both tanks and the device still won’t run, pull the spark plug to see if that is the problem. Just clean the spark plug or replace it.

Next, will be the fuel supply valve. If it has remained closed while cranking, then you need to open it to let more fuel through to the engine. If that doesn’t solve the problem, then check the battery.

If the battery is low on power, the generator should not start. It won’t even crank. If you hear cranking, then check the other sources first. If you do not hear any cranking then check the battery first.

If the battery is okay, then check the wire connections as well as the fuse. If the fuse is blown then the generator will not start. If your generator still does not start, call in a technician for further diagnosis and a solution.

Download The Onan 2500 LP Generator Manual


The best place to go for an owner’s manual would be the Cummins website. It has a list of all the manuals for all the generators it has made over the years. You can see that list at this link. That web page also has a parts manual in case you want to do your own troubleshooting.

One item to be aware of is that the different generators belong to different families. For example, the QG 2500 RM LP belongs to the KVD group while the QG 2500 LP belongs to the KV group.

There are different manuals for each group of generators so make sure you know which one yours belongs to. There is also a QG 2500i LP that belongs to the HGLAa series and it has a different manual.

This website not only sells Onan generators, but it also has the same manuals as the Cummins website. Under the add to the cart banner, you will see all the manuals listed including the part & installation booklets.

Finally, this website has a manual for this brand of generator. You may have to search the site to find your specific model so make sure you have your model number ready.

Some Additional Words

The Onan 2500 LP seems to be a very good generator to have installed in your RV. It should provide the backup power you need. Then, if anything goes wrong, it should be simple to fix without calling in a technician.

There is a short troubleshooting page in the owner’s manual which provides you with a good start in rectifying any problems that may have occurred. The key to preventing problems is to make sure you follow oil change instructions as well as do good maintenance to the generator.

A well-maintained generator should last you a very long time and have a smooth operation.

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