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Old 04-20-2020, 05:28 PM   #1
jimmyparker
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Default Onan QG 4000 RPM

I have a Onan QG 4000 generator in a class A MH that runs the same rpm with no load as it does at full load. Is this normal? I've had 4000's in the past and didn't remember them running at 3600 or so all the time. The generator has 236 hrs of usage. I pulled the air cleaner and checked to see if the throttle blade was intact and ok and it was.

Any help will be appreciated,
thanks

Jimmy Parker

Last edited by jimmyparker; 04-20-2020 at 06:05 PM. Reason: additional info
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Old 04-20-2020, 08:54 PM   #2
Rich Biebel
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Default Re: Onan QG 4000 RPM

Engine rpm is read with a Frequency counting volt/ohm meter.
62 Hz no load
58 Hz full load

And yes that is basically 3600 rpm all the time....each 1 Hz = 60 rpm of the engine
The generator end/rotor is spinning at the same speed as the engine and the AC frequency indicates engine speed..

That’s ideal numbers and the governor controls that.
Flyball type governor inside engine attached to the arm on top.
Spring tension and arm leverage are adjustable.
There is a low speed screw that may be interfering with governor arm action.
It’s on the carb and you should be able to pull on the governor arm and lower the engine speed.
If it does not come down some that screw needs to be backed up a little.

That’s the usual scenario when engine speed does not move much.
It usually causes them to overspeed once load is removed or at least it can cause that occasionally.

There really very simple but complicated ! Lol
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Old 04-21-2020, 11:20 AM   #3
jimmyparker
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Default Re: Onan QG 4000 RPM

Thanks Rich, I'm sure you have saved Class Racer members thousands of dollars with your expert advice.

I checked that governor throttle arm and it was not returning all the way to the set screw, I took a slight amount of tension off the governor spring and it now returns to the stop and does affect the running speed. I surprised that Onan still offers these generators and even more surprised the RV builders still install them.

Thanks again,

Jimmy Parker
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Old 04-21-2020, 12:07 PM   #4
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Default Re: Onan QG 4000 RPM

They are my favorite model and I own 2 myself....

Most Every Class C Motorhome has one.....

I have one in my trailer and one in my Class C Motorhome....

They are not like the older 1800 rpm units for sure and are far less durable.

Older models were twin cylinder flathead engines that ran 1800
From a 4 to a 7 KW

20 years ago they started making their modern versions....

Single cylinder 3600 rpm....on the QG 4000's......The 5.5 and 7kw's are twin cylinder and nothing like the 4's....

Onan stopped making their own engines back then and everything they build uses an import built engine......No big surprise....

For those that don't know.....
A modern Onan QG 4000 has NO low oil shutdown....
If it runs low on oil it will at the very least seize up and usually much worse.....

The aluminum rod usually blows up and takes out the engine.

They only hold about 1-1/2 quarts of oil and it should be changed often.....and checked often.....No filter.....splash oil....

I saw more than one that blew up and really busted up everything in there.....changing an engine is not a good option so it winds up being trashed....
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Old 04-22-2020, 12:57 PM   #5
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Default Re: Onan QG 4000 RPM

Quote:
Originally Posted by Rich Biebel View Post
They are my favorite model and I own 2 myself....

Most Every Class C Motorhome has one.....

I have one in my trailer and one in my Class C Motorhome....

They are not like the older 1800 rpm units for sure and are far less durable.

Older models were twin cylinder flathead engines that ran 1800
From a 4 to a 7 KW

20 years ago they started making their modern versions....

Single cylinder 3600 rpm....on the QG 4000's......The 5.5 and 7kw's are twin cylinder and nothing like the 4's....

Onan stopped making their own engines back then and everything they build uses an import built engine......No big surprise....

For those that don't know.....
A modern Onan QG 4000 has NO low oil shutdown....
If it runs low on oil it will at the very least seize up and usually much worse.....

The aluminum rod usually blows up and takes out the engine.

They only hold about 1-1/2 quarts of oil and it should be changed often.....and checked often.....No filter.....splash oil....

I saw more than one that blew up and really busted up everything in there.....changing an engine is not a good option so it winds up being trashed....
What oil do you like for this generator?
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Old 04-22-2020, 01:13 PM   #6
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Default Re: Onan QG 4000 RPM

Interested in Rich's recommendation as well. The oil fill tag attached by the Onan technician indicated a different oil than is recommended by their manual. My previous Onan was a larger model with filter and at the initial 50 hour change the oil looked better than this one did at 20 hours. Going to make sure I don't go past 30 hours without a change from now on.
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Old 04-22-2020, 01:30 PM   #7
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Default Re: Onan QG 4000 RPM

Onamax is the oil they sell for every machine they build

It's 15-40 which is/was commonly used in Diesel's for years.

I stopped buying it from Onan and have been using 15-40 Delvac. That is what our bulk supplier sells now and we buy it in bulk as well as in qt cases...

In winter I switched most commercial users of Onan's to a 10-30 oil

All air cooled engines work their oil over very hard.

Typical 7kw gas Onan's used in commercial trucks, when the oil is changed it's in bad shape if gone to many hours.....real bad!

Oil does more than lubricate.....it also helps to cool and carry heat away from various engine parts.

The 7kw's develop cylinder head failures from the heat.
Fresh oil helps....
Poor installs kills them and the same goes for the 4kw machines but not as bad.....

Using synthetic oil is not a bad idea but it still needs to be changed often because of how bad it deteriorates from the heat.....
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Old 04-22-2020, 06:05 PM   #8
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Default Re: Onan QG 4000 RPM

After I switched to 15W-40, I noticed that the oil consumption went down as well.
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Old 04-23-2020, 11:29 AM   #9
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Default Re: Onan QG 4000 RPM

Speaking of oil changes I am not sure the difference between the commercial QD 8000 and the regular QD 8000. I have two of the regular QD 8000 and I recently changed the outer panel to the commercial version to make the oil changes and fuel filter changes easier (for me). I wish all of them came with that removable panel. Seems like I hit the 150 hrs pretty quickly on each of them.

What is the real differences between the commercial and the regular Quiet Diesels other than that convenient panel?
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Old 04-23-2020, 08:05 PM   #10
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Default Re: Onan QG 4000 RPM

There is very little differences from most machines from RV to CM models.
The added side access door is for use in some trucks with limited access below the machine but direct access to that door area.
Many diesel pushers have the older 7.5 diesels. Very similar to the newer 8’s
Those diesel pushers more often than not have the generator fixed mounted in front. No side access. Bottom trap door for service only. Not fun to do.
Some of those MH’s have slide mounts for the generator.
I assume Onan just added the side door to cover various installs and access.
Diesel oil changes can go longer than 150 and 250 was what was their recommended hours for changes. Changing it more often does no harm that’s for sure. They only hold 3 qts
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