Onan shuts off while driving/hot

[jeremywatco]

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.

[bounder39zman]

a couple of comments on the problem with generator shutdowns in higher ambient temps; 1st...NEVER run a 4KY(microlite/Microquiet) or newer 5.5 and 7000 Onan gens
with service door removed (except for a quick adjustment maybe).
They will not run cooler, just the opposite. And the mufflers will get hot enough to melt the fiberglass covers. They come with a warning label on the base tray stating this. Hot weather seems to bring out the worst in these air cooled units. Vapor locking can occur if temp in gen compartment is high enough. we have acheived some success by moving fuel pump to cooler location, outside the gen compartment. Only do this on commercial applications, e.g., food trucks, grooming vans, etc.
Most often a fuel pump problem, as they can just stop pumping if they get hot enough. The other problem that we commonly see is the control board stops supplying voltage to fuel pump when it gets hot....usually will restart after a cool-down period. The intermittant nature of problem often makes diagnosis difficult

[ScottG]

DonSmith wrote:
Maybe the additional heat caused the oil pressure to spike?

More heat would actually cause lower oil pressure.

Cheers,
Scott

[darsben1]

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.

[Chum_lee]

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

[enblethen]

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.

[j-d]

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.

[DonSmith]

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.