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Old 05-11-2015, 05:51 AM   #1
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Generator oil consumption

When running our Onan RV QC 4000 for a few hours at a time I'm finding that I need to keep an eye on the oil level, as it needs to be topped off after a 1/2 day of running. Is this normal oil consumption?

Also, when removing the air filter in front of the Carburetor I notice some engine oil in the filter box, is this normal?
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Old 05-11-2015, 09:40 AM   #2
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No neither are normal. I have the same gen and do not use any oil at all. I'm sure someone can give you an answer on why their is oil in the filter box. But that doesn't seem good. Do you have a cummins dealer close by? Giving them a call might be your best bet.


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Old 05-11-2015, 10:41 AM   #3
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Not sure if generators have PCV valves or not, but that's what I would suspect was the problem causing this issue in a car. Also, I have heard of cars having a hole in a piston that increased the crankcase pressure and forced oil back into the breather. Definitely not normal.
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Old 05-11-2015, 11:39 AM   #4
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CoralReefer - it sounds from your description that you may have some excess oil consumption that's allowing oil to work its way back through the crancase ventilation system and that's the oil you see in the air filter box - the way to check this is by a cylinder compression test - first a dry test then a wet test - the wet test is done by putting a small amount of oil in the cylinder to see if there is a difference in compresiion readings - if there is then that indicates that your piston rings are worn - this will allow a small amount of compression pressure into the crankcase and that will pressurze the crankcase even more and that will usually start to push oil into the tube and into the air cleaner - the next test would be a cylindr leakage test and with that test you put compressed air through gauges into the cylinder and see what percentage of leakage there is - this can be done by a small engine shop or RV service facility to confirm that the oil control inside the engine is not efficient enough to keep the oil where it is supposed to be - the QC 4000 is a single cylinder small engine and uses these same tests as any other small engine and are used to detect internal mechanical problems - that tube that goes to the aircleaner goes into the valve cover and underneath the valve cover is a breather assembly that does the same thing as a PCV valve in an auto engine - if it is defective it will allow oil to go up the tube to the air cleaner as well so you can try and replace this first to see if that corrects the problem - I would do the testing as well to get an idea of the condition of the engine is in - other things that will contribut to this problem are overfilling the oil, using the wrong type of oil ( check your owners manual ) or the engine operating on the edge of overheating - this engine is air cooled and any restriction of the air intake or exhaust will cause the engine temperature to rise.
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Old 05-11-2015, 02:06 PM   #5
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Quote:
Originally Posted by coralreefer View Post
When running our Onan RV QC 4000 for a few hours at a time I'm finding that I need to keep an eye on the oil level, as it needs to be topped off after a 1/2 day of running. Is this normal oil consumption?

Also, when removing the air filter in front of the Carburetor I notice some engine oil in the filter box, is this normal?
Definitely not normal. How old is your generator? We have a 1997 Minni Winnie with the Onan 4000 and never had to add oil. Hope you figure it out soon.
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Old 05-11-2015, 04:56 PM   #6
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Is the carb vented? It could be a vent line that is blocked which would cause this.
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Old 05-14-2015, 10:57 AM   #7
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Quote:
Originally Posted by coralreefer View Post
When running our Onan RV QC 4000 for a few hours at a time I'm finding that I need to keep an eye on the oil level, as it needs to be topped off after a 1/2 day of running. Is this normal oil consumption?

Also, when removing the air filter in front of the Carburetor I notice some engine oil in the filter box, is this normal?
Coralreefer - Little bit more info please for us:
How many hours on your generator?
How do you use your generator typically? - While underway (driving) or parked stationary?
What weight of Oil do you use?
How are you checking it? Hot (right after running it) or cold/cool?

I'll give you my input on our Onan QC 4000, with almost 400hrs, mounted in our Class C motor home ( 3170DS):

If running our generator while underway (70% of the time due to Texas heat):
Then what you've noted about oil consumption (really oil burping through air filter/carb) is normal for us. Sometimes there is but just a few drops found after a 6+ hr drive in the air filter assembly... Sometimes nothing really noticeable... Sometimes it's an ounce maybe (more than a few drops for sure... enough to start pouring out onto epoxied circuit control board). Over 4 years of ownership I've been able to correlate and explain the amount of oil consumption/burping directly to the quality of roads I traveled on and/or the amount of extreme angles off of level the rig obtained while the generator was running.

When running our generator while stationary (boon docking) and reasonably level:
No real measurable about of oil consumption (or burping) even for extended long run cycles 8+ hours.

I have really good real world experience to correlate this with all our travels. If your running your generator while underway, there will be oil consumption (really mostly burping through the air filter assembly). When we run our generator while driving (again about 70% of the 400hrs are while underway), my habit is to check the oil at the very end of each day's travels or the beginning of the next day. Check while cool and add small amounts of oil at a time if needed. I do not fill above the halfway mark, as I see an increase of oil 'burping' if so.


To recap... IF your oil consumption is indeed while underway and IF while stationary you don't have any real amount of measurable consumption. I feel it is normal for this type of simple single cylinder air cooled 4 stroke engine. Take any lawnmower engine and operate it at near max output while shaking it and tipping it at angles, oil consumption does go up.
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Old 05-14-2015, 01:00 PM   #8
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Thanks to all that have replied. My generator has 225 hours on it, and it's in my 2011 sunseeker 2690.

I am using it when parked, and get the small pool of oil at the base of the air filter box, and then drops on the sealed electric panel below.

We live in FL and are running it all night for the AC, so putting about 6-8 hours on it at a time.

I check the oil when cool most of the time, before starting it up again the next time. I just did oil change and put SAE 30 oil in, due to our high heat in FL and the OEM recommendations.

Maybe it's me, but I find it hard to get enough oil in the engine before spilling out, and the dipstick only reads 1/2 - 3/4 full. And yes, I twist it all the way in and then back out to check it. Am I over filling and don't know it?

I've found that when using while driving I need at least 1/2 tank of gas or it shuts down.

I'm I bit worried about the oil that ends up on the outside of the engine sparking a fire, so I clean as much as I can if I know we're using it all night..
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Old 05-14-2015, 02:49 PM   #9
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We had the same generator in the MH we just traded in a few weeks ago, but it was a 2006 with something like 1,400 hours on it. There were a couple of times I saw minor oil (very minor) in the breather, like funfinder5 was describing. His explanation sounds very reasonable. When you change the oil in the engine, getting the new oil in is not easy. I had to put it in until it spilled over, then wait like half an hour for it to run down into the block and finish filling it. It will hold the amount indicated in the manuals (I think I remember it being 1.4 quarts), just have to be VERY patient. We ran ours almost exclusively while going down the road; never camped without shore power. Most of the hours were put on the unit before we bought it back in 2010.
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Old 05-14-2015, 08:57 PM   #10
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Coralreefer I don't know. What you are describing sounds a bit excessive as far as oil in the air breather. At most I've only needed to add about two ounces for about an 8 hour run, and only while underway on very hot summer days traveling through OK or LA.

Also I've always used 15W-40 diesel motor oil (Mobile) year round in Texas. John Deere runs the same weight so I have it on hand.
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