OK, the genset in my '08 A-bus 40QDP kicked over 50 hours so I dutifully bought three quarts (the book and a sticker on the genset both say 3 quarts) of Rotella T 15W-40 and the proper Onan (green box) oil filter and set up to change the oil. Before I began to drain the old oil I checked the level and it registered full on the dipstick so I ran the genset under load for 10 -15 minutes and drained the oil into a drain pan, changed the filter and added the three quarts of Rotella T. When I checked the level with the new oil it was a half quart low on the dipstick. So I carefully poured the old oil from the drain pan into a gallon jug, marked the level on the jug, dumped the old oil and filled the jug with a measured amount of water. It took 13 carefully measured cups of water to reach the level on the jug so that's 3 and a quarter quarts. I figure that, in the process of changing the oil I lost at least a quarter quart (on the ground, in rags, left in the old filter, in the drain pan, etc) so, from the factory the genset had about 3 1/2 quarts of oil in it. At this point I'm pretty much confused so I call Cummins/Onan and talk to a nice guy named Bill Rogers who is one of their techs. He is just as baffled as I am and can only say that all of his information indicates that three quarts is the right amount. Matter of fact, he is also interested in what other people who have done this before have to say about the issue.

As of now, based on his recommendation, I have very carefully added a small amount of oil to bring the level up to the full mark on the dipstick. Anyone out there with a similar experience?

Regards,
Joe Davis

I just had my Gen serviced @ Cummin South Chattanooga. They had done the service just 75 hrs./5 months ago. They reported that I was very low on oil. I have NO leaks and the tech said that they might have not filled properly last time. Maybe it does take more than Onan says.

Hi: I just registared in to make this comment. Hope you don't mind.

Can it be that the book lists 3 qts with out consideration for the filter? I know with my toad, book says 4 qts but it always takes an extra 1/2 quart to get to the full mark on the dip stick when the filter is changed.

Marty

I just had my oil changed at LandYachts in Jupiter, FL and it took about 3.25 quarts of 15w-40 Onamax. It generally takes 3 but sometimes they really allow the gallery to drain so it takes a little more to get the level back to the top of the hashed mark area on the dip stick.

I had a 2000 motorhome with a Onan 7.5 Quiet Diesel and it took 3.25 qts to fill to the Full mark after changing the oil and filter. In my 2005 Onan 7.5 QD it takes exactly 3 qts to fill to the Full mark.

I think the dipsticks were calibrated differently. Since Onan says 3 qts I would just add 3 qts and cleck the level every 8-10 hours of operation.

Thanks for the replies. The oil dipsitck being calibrated differently was what the Cummins/Onan tech came up with so, perhaps that is the explanation. The book does say very clearly 3 qts with filter. I will watch it closely in the near future.

Regards,
Joe Davis