RV Doctor – Oil Won’t Drain When Changing Oil in Generator

Dear RV Doctor,

We just purchased an RV with an Onan Marquis generator. We went to change the oil for the first time and after warming up the generator we could not get the oil to drain any faster than a drop at a time. We opened up the drain valve and unscrewed the filler cap. Other than that we’re not sure what to do.

Kandie Nield, (Hagerstown, MD)

Answer:

Kandie, I hate to be the one to ask this, but are you absolutely sure the crankcase is not simply empty or very low on oil now? I’d suggest pouring in about a half a quart, leaving the drain valve open and see if the new oil immediately drains. If it does so, that generator was quite low on oil when you went to change it. If the new oil, however, does not drain normally, then you apparently have a blockage inside the crankcase or in the drain valve itself.

You can try using a flashlight and mirror to see if any blockage is visible. If not, it may necessitate having the generator removed from the coach and the oil pan removed for a thorough cleaning.

But first pour a quart of cleaning solvent or very light oil into the crankcase and stir it around with a screwdriver reaching through the dipstick/cap cover. Perhaps that will dislodge or dilute any sludge blocking the drain opening. You may even try to snake a flexible wire up through the drain valve in case the blockage is only located there.

Be sure to flush it thoroughly and to fully drain everything in the crankcase before adding fresh oil. Don’t forget to replace the oil filter as well!

(Please feel free to comment, however, please also note that due to the volume of communications I receive from multiple channels I cannot guarantee a personal response in every instance. However, questions of an overall general interest may be considered and published in an upcoming RV Doctor column.)