Checking the Onan Oil

If your Onan will not start, there are two very common causes:

The gas in the gas tank is below the Onan pickup (this is supposed to be about ¼ tank – to prevent you from running your gas tank dry using the generator).

2) The oil level in the Onan generator is low.  The Onan has an oil level sensor to prevent the generator from being run with low oil.


Here is how to check the oil in your Onan: 1 : Locate your Onan.  It is a green box with a black access panel.  If you don’t know where it is located read this.   It will either be behind an access door on your Roadtrek or hanging underneath in the rear center.  If your Onan is underneath using some ramps made from 2x8 boards will provide a bit more working room.







P1050306Step 2: Remove the access cover.  Put a finger in each of the latches and pull up and out to remove the access door.  Remember when you go to reinstall it that the latches are at the bottom of the door.












Onan Circuit Breaker, Gas Filter, DipstickStep 3:  Locate the Dip Stick.  It is at the bottom center of the access panel.  Next to the fuel filter.  It is orange.  It may be rather dirty – like in this photo.


Step 4: Unscrew the dipstick.  Remove the dipstick and clean it off with a clean rag or a paper towel.  Be careful not to drop the dipstick down inside the generator box.  It will be very difficult (and perhaps impossible) to retrieve.







Onan - Oil fill next to fuel filter

Step 5: Check the oil level.   Note the XXXX area between the F (for Full) at the top and the L (for Low) at the bottom.  The Oil level needs to be in the XXXX area. Insert the dipstick back into tube but DO NOT screw it in.


Step 7:  Read the oil level.  Pull out the dipstick and note how high the oil comes on the stick. 


Step 8:  Add oil if low.  Oil is added through the same opening the dipstick came from.  If your Onan is under your Roadtrek using ketchup or other squeeze bottle will make adding oil a lot easier. 








Sitting on BucketStep 9:  Screw the dipstick back in.


Step 10:  Replace the Access Cover.  Remember the latches are at the bottom.  Make sure you get it on securely.  They are expensive to replace, and must be installed to run the generator for more than a short test.


Step 11: You are done!  Crawl out from under your Roadtrek or get off your bucket.


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