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Old 02-21-2017, 08:35 AM   #1
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Can you over fill the oil in the generator?

I am curious if it is possible to put to much oil in the generator (Onan RV QG 4000)? It seems with the design that you cannot. That it would just overflow the oil fill spout and drain out.
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Old 02-21-2017, 09:05 AM   #2
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I think the manual says to not overfill. Isn't the oil filler cap also a dip stick?
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Old 02-21-2017, 09:08 AM   #3
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Oh yes, the cap is the dipstick. I am just curious about the design as it seems that you really couldn't over fill it if you tried. I think that would be an awesome design if it is indeed built that way.
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Old 02-21-2017, 09:16 AM   #4
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Thank you for your question. I recently asked a question with not much response. I asked about two different readings on dipstick. First pull of dipstick reads low screw back in and pull out reads fine. Confused as to which is correct. But to what you asked I added oil once because of my confusion and generator would not start. I drained some out and all was good started right up. Wish I knew how to get correct reading.
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Old 02-21-2017, 09:24 AM   #5
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Quote:
Originally Posted by gmacklem View Post
I am curious if it is possible to put to much oil in the generator (Onan RV QG 4000)? It seems with the design that you cannot. That it would just overflow the oil fill spout and drain out.
Yes you can overfill.

The dipstick on the cap shows the full level an inch or so BELOW the threaded portion. If you filled the crankcase until the oil ran out the fill hole, it would be over filled.

Would it hurt anything if you did?
Probably not... but it may sling enough oil internally to where it could.
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Old 02-21-2017, 10:10 AM   #6
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Check operator's manual. Oil checking procedure may vary. Some will be with threads fully engaged, some with just threads touching which is a big difference. Check fill volume of oil required. Some air cooled engines are splash lubrication and some are full pressure lubrication via oil pump and galleries. Overfill may be significant enough to cause crank counterweights to move through oil and splatter all over, reduce performance, cause oil foaming and aeration (bubbles) in the oil, which isn't what you want going on in a pressure lube system. Hydraulic systems don't like air! You can also get enough oil on the cylinder walls to where the oil rings won't do their job properly and it will find it's way into the combustion chamber and burn off. There's a reason for fill and add marks and specs for how much capacity. Depends on how far off you are!
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Old 02-21-2017, 10:51 AM   #7
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Check operator's manual. Oil checking procedure may vary. Some will be with threads fully engaged, some with just threads touching which is a big difference. Check fill volume of oil required. Some air cooled engines are splash lubrication and some are full pressure lubrication via oil pump and galleries. Overfill may be significant enough to cause crank counterweights to move through oil and splatter all over, reduce performance, cause oil foaming and aeration (bubbles) in the oil, which isn't what you want going on in a pressure lube system. Hydraulic systems don't like air! You can also get enough oil on the cylinder walls to where the oil rings won't do their job properly and it will find it's way into the combustion chamber and burn off. There's a reason for fill and add marks and specs for how much capacity. Depends on how far off you are!
All true but OP asked only one question and was about a specific generator.
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Old 02-21-2017, 11:05 AM   #8
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Yes I agree with you that it seems or looks hard to overfill. We the unit level and changing the oil (which I want to do every 30 - 40 hours of run time so it really never gets that dirty) the quart and 1/2 fills it almost to the neck but not all the way.

A person could overfill by tilting the unit to allow more to go in or just taking it slowly and adding more slowly till it is ready to drip out. Both of these ways would be an intentional wrong doing.
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Old 02-21-2017, 12:19 PM   #9
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One does need to make sure the generator is level before checking and filling oil.
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Old 02-21-2017, 01:24 PM   #10
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"Originally Posted by jeff64
Check operator's manual. "

Operator's manual. You got an operator's manual with your RV?
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Old 02-21-2017, 03:04 PM   #11
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I do have some manuals, but not sure I have the generator manual (I bought the RV used). But I downloaded 2 different manuals from Onan and both warn against over filling. One says "Overfilling may cause foaming and engine shutdown". It just seems that they are so close to a design that can't be over filled that they should have done it that way.
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Old 02-21-2017, 04:07 PM   #12
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Trust your dipstick, as long as you are in between the A and F, or on the hash marks, or whatever indicator you have, oil level is good. Most manuals I've read say to screw it all the way in when reading level.

If you do overfill you will know as the exhaust will be very smoky
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Old 03-01-2017, 12:07 PM   #13
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I have the RV QG 4000 spec P. To check oil the dip stick must be screwed all the way in. With my unit level the oil is just about to the top of the filler neck and appears anymore would spill out. I just changed the oil for the first time and put the exact 1.6 quarts of oil that Onan says the unit takes back in and it comes right to the top of the filler spout when unit is level. I recorded it on YouTube if you want to see it. https://youtu.be/UJ-ZYRhZKsw
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