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

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

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

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....

Re: Onan QG 4000 RPM
 

What oil do you like for this generator?

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.

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.....

Re: Onan QG 4000 RPM
 

After I switched to 15W-40, I noticed that the oil consumption went down as well.
Dan

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?

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

Re: Onan QG 4000 RPM
 

Thanks for the info. I went with the recommended 150 hours for hot, dusty conditions which described sportsman parking in Division 4 and many of the others. :cool:

Re: Onan QG 4000 RPM
 

Good to know. I just bought 28’ trailer extra height. Looking at getting a generator. No a/c right now but want to put 2 15 units in it. So it will have that plus lights, plugs for charger air compressor etc. would an Onan 4000 be enough? Thanks Ed

Re: Onan QG 4000 RPM
 

I have noticed more racers are going to the inverter style generators like the Honda EU7000iS and the Honda EU3000iS.

They are very quiet and only run as many RPM as they need to cover the load.

However they appear to need to have the generator door opened and pulled out on a slide to get proper cooling.

Connecting an exhaust pipe on the EU3000iS may take a special kit.

Of course these generators are pretty expensive but other inverter generator are starting to show up on the market.

However the Onans are not inexpensive either.

Re: Onan QG 4000 RPM
 

4000 is barely enough for a trailer. I put a 6.5 in mine and it runs everything very easily. I bought an old Onan 6.5 with low hours for $500. It’s one of the 1800 rpm twin cylinder units. They are very quiet and reliable. Just search on Craig’s list or Facebook marketplace. There are usually some for sale there.

Re: Onan QG 4000 RPM
 

Ok thanks. I’ve found a few used in my area.

Re: Onan QG 4000 RPM
 

What are the model numbers for the low RPM (1800) Onan 6.5 RV gensets?

Anything to look for when shopping for one?

Thanks!

Re: Onan QG 4000 RPM
 

The older units have not been produced for about 20 years so any one you buy is at least that old.

The common models were BGE, NHM, NHE

The best ones were with black sheet metal covering the entire unit and they had electronic governors

BGE's are the most common. Usually green. Mechanical governors. Made in 4000-5000 and I think some 6500's

The date the machine was made is in the serial number.....First 4 numbers are year and month...

The older ones had points for ignition mounted in a box on top.

You would generally say the newer versions with electronic ignition triggering are more desirable.....BUT in reality they are not...

Mice love to nest in those units and they get in the control box and the lower portion of the generator itself. The ignition rotor device is plastic and is mounted between the rotor and engine and can and will easily be broken hitting anything the mice pile up in there.

Now you have to split the unit apart to replace the plastic ignition component. It is a flying magnet type...…

A points style unit is immune to that problem and the points are easy to change, clean, adjust.....

The old ones were built when Onan still built their own engines.....Very heavy duty and long life. They do have some issues like carbon buildup and various components that can fail but are good.

I own 2 New style 4000's and my trailer unit has many hours on it and has been fine. I use it anytime I'm racing all day pretty much everyday....

It will power all my lights including 500 watt quartz outside and interior fluorescents.....and a portable compressor....

The 4000 in my Motorhome runs a 15,000 BTU AC and a Microwave and a battery charging converter all at the same time with no problem and power to spare.....

I've seen many older units for sale on various sites and often they are SPRAY PAINT rebuilds......A can of Onan green paint is all they got after getting cleaned up....

Some major components are obsolete for the old ones and that's another problem...…

2000 was about when they stopped building the old flathead style units....

Onan engines were used in a long list of industrial applications. Welders, pumps, machines of all kinds and that basic design engine was made for years and years....

Re: Onan QG 4000 RPM
 

The one i had in my trailer before the 6.5 was a 4.0 CCK. On the name plate it said
Onan division of Studebaker. It still ran and made power when I pulled it out. I bet it has 20k hours on it.

Re: Onan QG 4000 RPM
 

If anybody is looking for a 4000 I have one.I bought it new to replace the one in our Class C and after 3 seasons it quit charging. A trip to the Onan Bridgeway dealer told me it was un reparable. I bought another new one, but while waiting on it to come in I went ahead and had a look at my old ( torn apart from Onan) unit. All that had happened, is the brushes had worn, twisted inside the brush holder, and mangled up one of the two small wires going to the brushes. Other than some of the insulation being removed from the wire, it was usable. I just put some small heatshrink on the wire, bought a new brush holder/brush set, and re assembled. It ran flawlessly on the bench and charges just fine. The thing looks new, its not even dirty. I'd like to get it out of my road , its here in the garage .. 700.00

740 297 0817

Re: Onan QG 4000 RPM
 

I pulled one out of a 2010 Class C today..

Around 2000hrs on it. Starter broke but the machine is a mess and had NO oil in it. I turned it over by hand at the blower wheel and it has NO compression. With no oil it probably broke the connecting rod.

Repairing the engine on a machine in extremely poor condition makes zero sense. It could have destroyed a lot inside that engine and replacing the complete engine is an even worse idea from a cost standpoint.

I ordered the owner a new machine. I will go pick it up as soon as it's ready for pickup and install it...1 or 2 days at most

The owner will be happy.....New generator.....But sir, please check the oil and leave the access door in place !!!

It says both things in big bold letters right on the front.....

A new style 4KY 4000 watt Onan does NOT have a low oil level shutdown....it will break the engine's connecting rod every time when oil gets so low that there is nothing visible on the dipstick....Seen it many times.....ZERO maintenance....for 2000hrs ? I am not sure on that one....

The owner actually asked me if the machine has oil in it like a car engine !!!