Help! Onan 4K generator refuses to start and stay on

When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.

bobndot wrote:
When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.

This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?

Kennyg
Unless it’s something weird cutting the ignition/spark off, my money is on plugged carb or carb issue.
Did it sit with gas/old gas in it for a while and not run?

Grit dog wrote:
Kennyg
Unless it’s something weird cutting the ignition/spark off, my money is on plugged carb or carb issue.
Did it sit with gas/old gas in it for a while and not run?

Yes, approx 6 months.

Grit dog wrote:

bobndot wrote:
When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.

This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?

also saw the video and I've since reduced the oil level to the half on the dip stick.

Onan 4K are notorious for simple issues causing problems.

The very first check you need to do is start it with the remote but do NOT let go of the “start” button when it starts.

If it continues to run, hold the button for 30 seconds then let go. If it stalls right away again, then get a known good battery or another vehicle and put booster cables on the house battery and repeat the same test again.

If it continues to run with the booster cables the voltage in the house battery is too low. Charge or replace it.

If it doesn’t continue to run, it’s a fuel issue.

Grit dog wrote:

bobndot wrote:
When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.

This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?

Dipstick engineering can be tricky business and requires 8 addition years of residency before they let you loose on a real generator. :B

Onan RV recommends changing the oil every 100 hours or once a year, whichever comes first. It only takes about 20 minutes and you will be good to go for the season. You will need a T30 torx bit, a 12mm socket, an oil pan, a funnel and 1.6 quarts of SAE30 or 15W-40 oil.

^Awesome Thanks!’
That’s good seems about the amount I got in there.

Kennyg. Yeah if the battery deal isn’t the problem. Not likely if you’re using the rig.
Then I’d probably take the carb apart and clean er out.

Hi KennyG,

I had a problem last fall with our Onan 4000 generator. It would self-shut down after 20 minutes running. I replaced the fuel pump with fuel filter just yesterday and the generator is perfect again.

The fuel pump was not easy to replace, but can be done. I highly recommend you consider replacing your fuel pump & fuel filter together. I recommend getting one with the exit tube like this (like the original one) to avoid a potential interference problem that I dealt with with the other available design.


Everyone on these RV forums quickly zero in on the carburetor being the problem, most especially because the unit sat idle for too long and bad gas in the carb gumming it up and such. At risk of insulting others, I don't agree.
I would replace the fuel pump and fuel filter together. It's surely cheap enough. It's all in the labor.

If you decide to do it, first disconnect every battery for the house and chassis. You will need to disconnect lots of wires in the area, remove the solenoid, then the control module. There is a 30 pin connector plugged to the underside of the control module that is very hard to access. I pulled every cable and wire harness out from the work area to gain enough work space.

When disconnecting and removing the fuel pump, make sure to first protect that 30 pin connector with a good rag to absorb any spilt gas.

Repeating what I said many months ago here in this subject, I never run my generator during storage which is typically 7 months but has been as long as 2.5 years, with the gas in the main tank being that old. Starting involves a lot of pump-priming, then chugs a bit and soon smooths out. The main chassis engine starts right up like it ran just the day before.

Carbs for simple engines are a lot more forgiving than people give credit.

Ron ... I'm wondering if the same aging gasoline chemistry issue that causes Onan carbs to gunk up can also cause Onan fuel pumps and filters to gunk up?

To maybe help prevent the above, perhaps we should add the red-colored gasoline maintanier fluid in our motorhome's main gasoline tank for Onan generator protection. Just add a little bit of this fluid into the main tank whenever we gas up the motorhome - or a least add the fluid in the last tank of motorhome gas before we fire up the Onan a final time when camping - so that the Onan gasoline supply components wind up being exposed to treated gas from the motorhome's main fuel tank.

(We're fortunate in that we store our motorhome at home and outside. It's in a rural area, so we can run the Onan generator about once a month to keep it's gasoline components flushed out with somewhat fresh gas from the big chassis tank ... without bothering any neighbors.)