Hi there,Having an annoying issue with my Onan 4000 gas generator that is only an issue while driving the motorhome. While stationary its perfect.So if the genset is running while driving down the road we have found that if it is really hot out and/or driving up a grade while it is hot out the genset will shutoff and refuse to run until conditions change.The genset is located right behind the engine on our 2014 Fleetwood Storm and by thinking is that excessive engine heat is making its way to the genset and causing it to overheat.I've made sure oil levels are good and that the fuel level is good.Yesterday I was driving home from the Sierra's and it was about 109 degree's outside. Wasn't the best drive home when the coach A/C couldnt be ran as the generator wasnt cooperating.Any thoughts? Anyone else having this issue? If it is a heat issue I am wondering if there is some way to modify the genset compartment to allow better outside ventilation.

I had a similar issue with my 1999 Holiday Rambler on the Onan 5500. I tried to solve it many times, but was unsuccessful, however after changing out the oil pressure switch the problem seemed to be reduced but not eliminated. Maybe the additional heat caused the oil pressure to spike? I know that on my newer Tiffin coach, with an ONAN 7000 aboard I haven't seen this problem as yet. This unit has an engine cover which is easily removable. If the purpose of this insulated cover is primarily to reduce noise, maybe removing it in ver hot weather might circulate more air around the engine. Just a thought.

Please provide Model and Spec for the ONAN.Do you know how it gets its fuel. Is it direct from the main tank, or tapped into one of the lines feeding the road engine?Was your gas tank low? Road engine would still run, but gas would slosh away from the genset's pickup. If you have an ONAN 4KY generator, it probably does NOT have a Low Oil Level switch. It also won't have anything like an Oil Pressure Switch since it's splash lubed. No oil pump, no oil filter. Kinda like a small mower engine.

Some installations do not allow for the genset to get enough air to keep it cool while the rig is in motion. It could be overheating and shuts down.

A shot in the dark here. I believe the owners manual states the upper and lower operating temperature limits within. (read it!) I don't know if there is an internal switch/sensor that controls that or not, but, if the ambient temperature is in the 109 degree F range, the temperature at the road surface behind the engine compartment in a Class A Fleetwood gasser would surely be well above that. If so, vapor lock would be a possibility.You did mention that this condition doesn't occur at lower temps?Chum lee

Some people found when faced with shutdown for unknown reasons that moving the fuel pump off the generator (it is an electric pump)to a cooler place cleared the problem up.

Onan shuts off while driving/hot | Good Sam Community

eHoefler
Explorer II
Jul 08, 2017
Low oil level switch shutting it down while in motion, OP stated while climbing a grade it shut down.
jeremywatco
Explorer
Jul 08, 2017
Thanks for all the responses. Yes this is an Onan 4000 without oil pressure, its a splash kind.

I have only noticed this behavior when its hot outside while in motion.

I'll see how hard it is to move the fuel pump.
dougrainer
Nomad
Jul 08, 2017
Years ago Onan Diesel Gensets had the same problem in Transit. They were mounted up front on Diesel Pushers and when in transit the design of the fresh air intake could NOT pull enough adequate air to keep the Genset from overheating. Onan's solution was simple. You installed the Onan lower air dam that stuck DOWN from the bottom of the genset in front and that allowed the Genset blower wheel to then pull up enough air. The Dam just stuck down about 3 inches. Maybe this is a similar problem and solution. I would be contacting your local Cummins/Onan service center. Doug
timmac
Explorer
Jul 08, 2017
I fix my 5.5 Onan from over heating, maybe I will post pics and explain what I had done to stop it from over heating.
tippytoe
Explorer
Jul 09, 2017
About a year ago maybe, there were problems with Fleetwood class C's (and Jaycos also) that have one roof A/C, with the 4000 kw generator installed on left side right behind the front wheel. The factory fixes I believe then was to do some or all of these things: too provide a fresh air intake through the removable cover, move or add fuel pump to near gas tank, move or insulate exhaust pipe so it's not in air intake flow, add sheet metal shield under generator to keep vehicle engine heat away.

There were a lot of discussions of this on this and other forums, but I couldn't seem to instantly find them at the moment.

By the way, our class A with two A/C's and the 5500 generator (behind the left front wheel) came with the added sheet metal shields.
tippytoe
Explorer
Jul 09, 2017
I just found a link I had saved - here it is:

http://www.irv2.com/forums/f121/ace-generator-stops-running-code-36-a-125555-61.html
shannonjerry
Explorer
Sep 17, 2021
We have had this problem twice while traveling. Once was traveling from IL to North Carolina through a ton of mountains and struggled to figure out why as after that all seemed fine. Today we got stuck in Chicago area with rush hour traffic of abrupt stop and goes and I figured out not a mechanical problem per say but a fuel splashing around problem messing up fuel sensors. Hence going through mountains the fuel is moving to one side of tank or other making sensor think low on gas. Same when have to come to a faster stop than normal! Once back to a normal pace and flat surface all works great! Really can't fix it. It is working to detect what it knows of a fuel tank on level ground.
04fxsts
Explorer
Sep 18, 2021
Last year coming home through Montana around 106 deg. we were just running the engine air and it kept us OK. We pulled into a Walmart to spend the night and the generator would start but shut off. The generator was so hot you could not keep your hand on it so figuring vapor lock. Found a nearby campground with electric and in the morning everything had cooled down and all was fine.
I have wondered if having the generator running would have kept it cooler and running. If I get in that situation again I plan to have the generator running. Maybe the air circulating will keep things cooler? Jim.
wa8yxm
Explorer III
Sep 18, 2021
Yes. if it shuts down (READ THE FINE MANUAL FOR SPECIFICS) you can press the stop stich. I forget how long but I think it's a tap.. And the active light will flash.. ONE of the fault codes is exhaust over temp

You read the codes (The repeat over and over)
if one code you will get like 3 blinks. 2 blinks 4 blinks . . 3 2 4

if two (Or more) 3 2 4... 2 4 2.. 3 2 4.. 2 4 2.. And so on.

Then you RTFM and.. Well sometimes the code helps. (Sometimes not so much)
Dkbrock911
Explorer
Nov 21, 2024
4000 onan.Will run great while parked. Driving it cuts off about 20 minutes into trip. It’s 42 degrees, so I don’t think it’s heat. However I have replaced carb, fuel pump, air filter, fuel lines are wrapped in heat shield, fuel pump is wrapped in heat shield, inline fuel pump was installed by fuel tank.I took outer rv door, not generator cover off.That didn’t help. Any is help appreciated.
- way2roll
  Navigator II
  Nov 21, 2024
  Hi and welcome. You are posting a question as a response in a thread that's 7 years old. You may find it beneficial to ask your question in a new post as it's likely to get more answers than being buried in a very old thread.
  That said, have you checked your wiring? A loose ground could cause your genset to stop running - not moving keeps it connected while driving it may jar it loose. Also, is it throwing a code? Gensets require constant power from the batteries to keep the fuel solenoid open.

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