Onan dies in the Heat

I have experienced this twice. First time with my 28 foot Weekend Warrior. Same generator as yours. When it got hot out that thing would just over heat just like yours is. I just sat a small small fan under it blowing up and never had another problem. Ran hundreds of hours like that in 90+ heat. On my 36V Jayco Recon it was fuel pumps. The Onan pump would overheat and die. After the second one I went to Auto Zone and bought a $30.00 electric pump and placed it back at the fuel tank where it should be. Electric pumps push fuel great, but really cant pull fuel and over heat. I used a 3 to 4 PSI pump. If you do this just check and see what psi the pump in your genny runs at. Some Onans are 2, some are 4. Mine has been running hundreds of trouble free hours like this.

Bedlam wrote:

Vulcanmars wrote:
If it's gas (not LPG) most have an adjustment for higher elevation on the carb. High elevation = lean fuel mix= runs hotter.
If it continues to die you may have a fuel pump going south.

Higher elevations result in a rich burn if jetted for sea level due to less air available. I have noticed more smell from the exhaust on my gasoline 5500 and LPG 2500 at elevation but never had plug fouling to worry about rejetting.

Duh, thanks had a senior moment.

Dwight45 wrote:
The fault code is 36. Again this is a brand new unit. Plenty of gas in the tank. Runs fine with the compartment door open. Not at high altitude.
Thanks

Sounds like heat is your problem. I also thought at 1 point it was mine also. In PHX on 115° days running my gen and burnt myself trying to flip the breaker switch in the genny compartment... It does run hot when its hot out. Air cooled motors are like that. As far as I know, there is no engine shut down or fault code for overheat on the Onan HGJAB(iirr) carb 5000 series.

So if it does stop from overheat, was told by an old timer Onan genny dealer in Phx, that when they get really really hot from blocked air flow the oil starts to boil/foam and that shuts it down on oil switch. But you did not have a oil fault code, so it might be hot seizing up..? Hopefully not.

offtohavasu wrote:
Make sure it's vented properly under the coach.

Agree with offtohavasu, Thats is what I'd check also...
Should be an area underneath the genny that sucks air in, and another that blows out hot air. Make sure the air inlet and outlet openings
in the bottom of the genset are not restricted in any way. Without the genny cover on the fan won't circulate air thru the genny correctly, but it will run like that.

Here is the troubleshooting guide from the manual for fault code 36, it is a generic code that says without fault condition.So that does help cut down on the possible problems.
GENSET STOPPED WITHOUT FAULT CONDITION – FAULT CODE 36

Logic: RPM less than 500 and Sense Voltage S1–S2 at 0 VAC when no other fault condition occurred
Possible Causes: Auto Gen Start (AGS), fuel supply, air fuel mixture, exhaust system, loads, Inverter/Charger,
choke, demand regulator, carburetor, generator drive system, generator windings, ignition, wire connections
Diagnosis & Repair:
1. Verify that Last Fault is FC 36: Yes, continue diagnosis; No, troubleshoot actual last fault.
2. Verify whether AGS stopped genset: Yes, disable AGS or explain AGS function to customer (see
PSB-666); No, continue diagnosis.
3. Verify engine rotation manually: repair engine damage as necessary.
4. Disconnect genset control P1 connector, verify P1 pins are fully inserted and inspect pin condition per
PSB–676: insert, repair or replace pins as necessary.
5. Reconnect P1 connector and test run genset for fault occurrence: repair or replace pins in connector as
necessary.
6. Check air filter cleanliness; replace air filter as necessary.
7. Check for blocked or damaged exhaust system: repair or replace exhaust components as necessary.
8. Measure AC current while running genset with vehicle loads: identify faulty or short cycling loads.
9. Determine battery charge rate (typical default is 80 percent): if adjustable reduce to 30 percent.
10. Measure genset load capability with shop load bank.
11. HGJAD only – Run genset in Engine Run Only and externally excite field F1–F2 with 12 VDC or 24 VDC
and measure main and quadrature winding AC output.
12. Non EFI – Verify genset operation and outputs with Break-Out Tool 420–0603 and Instruction Sheet
R1098.
13. Measure AC frequency while changing engine rpm to determine if frequency response matches engine
rpm response: repair damaged generator drive system as necessary.

Since this is a new unit, take it back to the dealer for resolution. You do not want to make changes that may be used against you to void your warranty. My 5500 ran for hundreds of hours without issue and yours should too.

Make sure it's vented properly under the coach.

Forgot to say that it's so hot in the compartment that you can hardly touch anything. I propped the compartment door open and ran it all night for AC. No problem.

Dwight

The fault code is 36. Again this is a brand new unit. Plenty of gas in the tank. Runs fine with the compartment door open. Not at high altitude.

Thanks
Dwight

Dwight45 wrote:
I'm having this problem with a brand new 5500 onan. If I prop open the generator compartment door it runs fine. Close the door and it overheats. Still think it's the fuel pump?

Dwight

Go in your Onan manual and look to the section that completely explains trouble codes. Go to your TH and check what trouble code yours has stored.
If you haven't got it figured out by then, come back here and tell us what trouble code(S)you got.

Until you do this, everything is just a wild guess.....

I'm having this problem with a brand new 5500 onan. If I prop open the generator compartment door it runs fine. Close the door and it overheats. Still think it's the fuel pump?

Dwight

Vulcanmars wrote:
If it's gas (not LPG) most have an adjustment for higher elevation on the carb. High elevation = lean fuel mix= runs hotter.
If it continues to die you may have a fuel pump going south.

Higher elevations result in a rich burn if jetted for sea level due to less air available. I have noticed more smell from the exhaust on my gasoline 5500 and LPG 2500 at elevation but never had plug fouling to worry about rejetting.

I agree that a weak/failing fuel pump would cause issues when ambient temperatures are high. Altitude should not effect the pump, but a partially clogged fuel filter or fuel tank vent will make a pump work harder than it should.