If your Roadtrek is equipped with an Onan 2800/2500 there are a few things you should know how to do. One of them is checking the oil level. Many Onans have a low oil cut-off sensor to prevent them from running if the oil is low.

So if your Onan will not start or it dies while running the oil level should be second on your list to check (first make sure you have more than 1/4 tank of gas) .  Unfortunately for many owners, that means crawling under your Roadtrek.  Find a parking spot where you can overhang a downhill to make things easier.  Or you can use leveling blocks to raise the back of the Roadtrek for more clearance (use your emergency brake and chocks).

Before you crawl underneath get a flashlight and a rag or a few paper towels.  A tablecloth, tarp, or a patio mat placed on the  ground will make things a bit more pleasant.  Once you get underneath this is what you will see:

Onan 2800 is located under the center rear in newer Roadtreks.

Onan 2800 located under the center rear

If you have an older Roadtrek with a compartment mounted Onan,   you won’t have to do any crawling.

Open the Onan access panel door by pulling up and then out on the latches.  Set the panel aside and be careful to get it securely re-installed.


Behind the panel you will see (click on photo to enlarge):

Here is behind the Onan Access Panel

Here is what is behind the Onan Access Panel

Note:  If you have Sprinter you will have the Onan 2500 which is the propane version.  It will not have a carburetor like the gas powered 2800 shown  in this photo.  Consider printing a copy of this photo and carrying it in your Roadtrek.  If you are physically unable to check your oil, the young guy in the next campsite might be recruited for the task!  With a photo you can shown him what to do.


Dipstick is next to the fuel filter
Note: Circuit Breaker is Off, should be On

Next locate the orange dipstick.  It might be a bit dirty, but it is next to the fuel filter, roughly in the center.  Unscrew it and wipe it off with a rag or paper towel.  Then insert the dipstick into the filler hole but DO NOT screw it in.  This is different from all the bigger Onan generators (sometimes RV dealers get it wrong – one reason for low oil).


Oil should be in the XXXX area

Oil should be in the XXXX area

Now pull out the dipstick and examine the oil level with your flashlight.  The oil level should be in the hatch marked area between the F (full) at the top and the L (low) at the bottom.  Add oil if necessary.  Since the Onan only takes one quart of oil, it will not need much if it is a little low.  Several people have used plastic squeeze bottles with a spout (think those red and yellow ketchup and mustard bottles you see in some restaurants)  for adding oil a squirt at a time.  A couple of squirts may be all you need.  Add some and check the level until you have the oil level in the correct range.

Internal Onan Control Panel

Internal Onan Control Panel

With the level adjusted, screw the dipstick back in.  You can test to see if adding oil fixed your problem by pushing on the Start/Stop switch below the air filter.  Does it run?  Great!  Push stop and you are ready to button her up.   If not, your problem is elsewhere and requires more extensive troubleshooting.   We have some troubleshooting tables on our website.

Now re-install the Onan access door.  Remember the latches are at the bottom (you will struggle a long time if you try to install it with the latches at the top – don’t ask how we know).  Take extra care to make sure you get the door securely latched because more than one Roadtrek owner has lost an Onan access panel on the road.   Should you loose the panel, do not run the generator  more than a couple of minutes without covering the opening or it will not cool properly.  And since a replacement access panel costs nearly $100, you really don’t want to loose it.

Note:  If you have a 2013 Roadtrek you may have the newest version of the Onan 2500/2800.  Consult your manual, many things have changed.