Leak in 7500 watt Onan Diesel Generator

Just to be more specific, if you look at the drain plug the hole the oil comes out is the one directly above the O in Oil. It doesn’t come out of any of those other holes.

I know you said it's not the filter but let's back up. Has anything been serviced recently? Are you positive the filter is tight enough, I've seen a lot of loose filters. If it was serviced be sure they didnt double gasket it. I'm sure it's a tight fit for everyting but it would be good to see exactly where it's coming from before you pull it out. If you can run it while it's out that's good. I bought a $15.00 flex snake camera that can connect to a computer or cell phone that might let you sneak in and look closer. Brake cleaner and an compressor with air blow nozzle will dry things up.

Is that rectangular cover riveted on? Is it a possible place where you may be able to see more?

That "rectangular cover" is the access door to replace the oil filter. Squeeze the two small sq. holes in that panel and the door will open and allow you to see and replace the oil filter and fuel filter.

I would look in there and clean around the oil filter, if you haven't done that, before doing anything else. That hole looks to be right near the oil filter.

I said it’s not the filter because I just had it serviced thinking that’s where it was coming from, and it wasn’t. We ran the generator with the cover off and the leak wasn’t in there. Changed the oil, replaced the filter and the exact same leak reappeared from the hole I described.

msmith1199 wrote:
I said it’s not the filter because I just had it serviced thinking that’s where it was coming from, and it wasn’t. We ran the generator with the cover off and the leak wasn’t in there. Changed the oil, replaced the filter and the exact same leak reappeared from the hole I described.

They can be tricky. Long ago I remember having a brand new JD lawn tractor leaking oil on the showroom floor and cleaned it and thought it was the pan gasket. Put it back out there and still leaking. I pulled the engine again and cleaned it real well and let it sit. The pan/base was cast iron and hard a pin hole porus casting. Ever since then I'm big on seeing it for darn sure. You could have a valve cover gasket, breather or gasket somwhere. Again, the trick is gettig it dried up and seeing exactly where it's coming from. You may also get some of the covers out of the way and find something obvious.

You might look at one of those cameras since they are cheap.

The problem is the leak is behind that hole. If you look at the photo you can see the object the holes are in is part of the generator casing and the generator mounts are screwed into it. What it looks like to me is I have to pull the generator out even to access that part of the casing to remove it to even see where the leak is. I do have a borescope camera so I’ll try to get up under there and see if I can find someplace to get access to put the camera in, but those existing holes aren’t big enough. Anyway, if I have to pull the generator out that’s above my skill level and I don’t have the tools to do it anyway so I’ll have to take it to a shop. I’m just trying to figure out if there is any chance there is an easier way. I’m doubting there is.

Hi MSMITH, the oil dip stick tube on these onans terminates in a rubber 90 elbo that goes into engine. that's most likely where your leak is. I don't know exactly how you can get to it but try the front cover. good luck, OILCAN.

I went and talked to an Onan person and got back under and looked at it a lot better. The only way to get to where ever that leak is would be to remove the generator from the RV. I also looked for how to do that and with the right equipment it doesn’t look too difficult. In fact looks like it can be removed with a motorcycle lift.

But before I did all that, I decided to go ahead and start the generator and let it run under full load for a while. So I let it run for close to an hour and the longer it ran the more the leak slowed until it’s down to about one drip every two or three minutes. Although I’m no mechanic, I suspect I let it sit too long without significant use. The motorhome has mostly been in storage for the last three years and when I have used it we’ve been in full hookup sites. I try and start the generator often, but not as often as I should. So for now, I’m just going to use the generator and see what happens. I suspect maybe I let it sit too much and somethings dried out and the oil leak started. As I use it those things that dried are getting lubed again and the leak is stopping. I’ll just keep an eye on the oil level. After running it for an hour the spot on the ground wasn’t very big and there was no noticeable drop in the oil level on the dip stick. So I’ll just keep a close eye and see what happens.