Cummins Onan LP generator oil consumption

[David-and-Cheryl]

I have a Cummins Onan RV QG 5500 Marquis Gold propane generator (model HGJAB) installed in our 2013 Landmark.

The generator is consuming about one quart of oil for every 40 hours of operation. Most of the time it's running, it's under about an 80% load (~35-37 amps), although the actual load % may be higher because we're at 6,800' elevation, which I know impacts the maximum power the generator can produce. The ambient temperature is around 90º.

I see no oil leaks, no indication of oil residue in the exhaust pipe, and no visible exhaust plume.

Is this a normal level of oil consumption under these conditions? If not, where would the oil be going?

 

[Flick]

I have a Cummins Onan RV QG 5500 Marquis Gold propane generator (model HGJAB) installed in our 2013 Landmark.

The generator is consuming about one quart of oil for every 40 hours of operation. Most of the time it's running, it's under about an 80% load (~35-37 amps), although the actual load % may be higher because we're at 6,800' elevation, which I know impacts the maximum power the generator can produce. The ambient temperature is around 90º.

I see no oil leaks, no indication of oil residue in the exhaust pipe, and no visible exhaust plume.

Is this a normal level of oil consumption under these conditions? If not, where would the oil be going?

There is only one possible answer. Your engine is burning the oil thru either blow by (which is worn compression rings), bad valve guide seats or a combination of several other possible reasons.
You didn’t say how many hours the engine has on it, but a lot of these problems can be caused by infrequent oil changes in older engines.
If the engine is new, then perhaps a claim to Cummins Onan is in order.
I think the recommended oil is 30w. Otherwise, the oil is likely to be to thin to handle the heat and could create the oil usage.
Normally, these engines can run for an entire season with only occasionally having to be topped of.
You said also that there is no oil residue but with the summer heat, it is probably being burned without notice.

 

[danemayer]

I have to change the oil long before getting 40 hours of run time.

 

[Flick]

I have to change the oil long before getting 40 hours of run time.

Well, to each his own on how we manage our engines. I change mine every 100hrs or once a year depending which comes first. Being a mechanic for years, we were always schooled that 1hr equals 50 miles traveled (average).
My new farm tractors go 600hrs recommended change by Case/Farmall. Now I’m not recommending that for our generators.

 

[David-and-Cheryl]

There is only one possible answer. Your engine is burning the oil thru either blow by (which is worn compression rings), bad valve guide seats or a combination of several other possible reasons.
You didn’t say how many hours the engine has on it, but a lot of these problems can be caused by infrequent oil changes in older engines.
If the engine is new, then perhaps a claim to Cummins Onan is in order.
I think the recommended oil is 30w. Otherwise, the oil is likely to be to thin to handle the heat and could create the oil usage.
Normally, these engines can run for an entire season with only occasionally having to be topped of.
You said also that there is no oil residue but with the summer heat, it is probably being burned without notice.

That's what I'm afraid of. I can't figure anywhere else it could be going.

The genset has 298 hours on it. 170 of those are in the last few months, while we've been boondocking on a friend's property.

The Cummins manual calls for an oil change every 150 hours or 12 months, which I've done. It's always been because of passage of time, not usage hours, until this summer.

I've been using Shell Rotella T4 synthetic 15W-40, which is an alternative to straight 30w allowed in the manual. I was doing that to allow for wintertime usage, although I probably could have switched to 30w at the last oil change since I'm using it so much. But in any case, I think it's unlikely that the oil is the problem. (However, I did buy the rig used after 2 years, and the previous owner had about 50 hours on the genset, so I don't know what kind of care it received during that time.)

I just noticed one other thing: there is a thin film of oil in the air filter enclosure. It's nowhere near the amount I've been losing, but maybe that offers a clue as to what's wrong?

I guess I'll be taking it in to a Cummins Onan service center once we leave here in the fall. (The closest one is 2 1/2 hours away.) Until then, I'll continue to watch the oil level and add oil as needed.

- - - Updated - - -

I have to change the oil long before getting 40 hours of run time.

Why, Dan? Do you mean because 12 months elapse? Or for some other reason?

 

[avvidclif]

I have 5500 EVAP gas version and change the oil every 100 hrs (~450 hrs now) I use straight 30wt non-synthetic and have yet to have to add oil between changes. When in use I shut it down once every 24 hrs and check the oil.

I would go to a straight 30w oil not synthetic and see what happens. You might be surprised.

 

[David-and-Cheryl]

I have the later model 5500 EVAP and change the oil every 100 hrs (~450 hrs now) I use straight 30wt non-synthetic and have yet to have to add oil between changes. When in use I shut it down once every 24 hrs and check the oil.

I would go to a straight 30w oil not synthetic and see what happens. You might be surprised.

I assume I'd need to drain the synthetic and change the filter if I was going to change to straight 30w, right? It's not a good idea to mix oils? (Of course I just changed the oil and filter 25 hours ago.)

 

[danemayer]

Why, Dan? Do you mean because 12 months elapse? Or for some other reason?

I run it a few hours per year so oil changes are by time, not usage.

 

[Flick]

I assume I'd need to drain the synthetic and change the filter if I was going to change to straight 30w, right? It's not a good idea to mix oils? (Of course I just changed the oil and filter 25 hours ago.)

Cliff’s suggestion is good. I think I’d change to a straight 30w quality oil, perhaps one for higher mileage vehicles which of course means perhaps that it has less additives, etc. Good thing is it’s easy to do and can be done for $20. Synthetic oil has more cleaning agents in it and could be a part of the problem.
In the meantime, just keep an eye on it and if gets worse, let someone do a compression check which will tell you a lot.
And yes, change the filter and never mix oils.

 

[David-and-Cheryl]

Cliff’s suggestion is good. I think I’d change to a straight 30w quality oil, perhaps one for higher mileage vehicles which of course means perhaps that it has less additives, etc. Good thing is it’s easy to do and can be done for $20. Synthetic oil has more cleaning agents in it and could be a part of the problem.
In the meantime, just keep an eye on it and if gets worse, let someone do a compression check which will tell you a lot.
And yes, change the filter and never mix oils.

OK, thanks everyone. I'm going to get some of the OnaMax 30w (might as well go with the manufacturer's recommended oil to rule out other issues with the oil itself) and a new filter and change to that. We'll see what happens.

If the oil consumption still doesn't decrease, I might then try some STP High Mileage Oil Treatment + Stop Leak, which seems to work for a lot of people (although I couldn't find any reviews specifically for Onan generators).

 

[esscobra]

little over 500hrs on mine and always used the cummins oil and filter - no real burn generally run for 3-4 days straight and don't have any significant useage- you can get filters and oil from amazon

 

[Angler]

My last 5500 generator had 2700 hours on it. Always used straight 30w oil.