Onan generator shuts down after 1 minute

[bigeyes]

I have an Onan 7.5 Quiet Diesel Generator on my 2004 Expedition. When I start the generator, it runs for about 1 minute and shuts down. The shut down code displayed is - primary 1, and secondary 33. The manual says that is a shut down code for overheating. Clearly it is not overheating in 1 minute. It will restart almost immediately but again runs for about a minute and shuts down. Have changed all filters and fluids. Any ideas on how to fix this problem would be appreciated.

[Flagelpater]

What does the manual state as a cause for code 33? Have you checked the cooling air inlet and outlet for blockage. How long since it did run okay? Do you have any electrical load on the GenSet? What is your ambient temperature?

[bigeyes]

The manual says its an overheat problem. I put a new air filter in, but did not see anything in the inlet or outlet. It last ran about a month ago. temps have been in the 60s and 70s. No load on gen set.

[Flagelpater]

Did it run okay after you changed the filter? Are there birds or other nesting animals in your area that could have clogged the air inlet? Can you be sure nothing is blocking the cooling air? As you know, one minute is a very short time for it to overheat with the cooling system working properly. I would also expect it to run less than one minute on the second run if it was actually overheating, not taking the full minute the second time. Can you see if a wire may be shorting to ground on the temp sensor lead? as you can tell I am not an expert troubleshooting this unit. Hopefully an expert will chime in shortly.

[Gary RVRoamer]

Since it probably didn't overheat that fast (UNLESS there is no coolant at all in the system - did you check?), I would suspect a failed coolant temp sensor. Or a disconnected wire to the sensor (but heaven's know where it might be!).

[AFChap]

My Onan 7.5 did the same thing last April ...you said you changed "all fluids" ...I presume that includes coolant. I believe there is air in the coolant system. Here's what I did to cure mine, straight from my service records. It has run a lot since then with no problem.

"First time run since 13 Apr service, started generator, ran fine but no power output, found breaker on generator in OFF position, turned it on, generator died in less than one minute. Restarted. Ran less than one minute and died. First stage code 1 blink, "high temp." Restarted and again died in less than one minute with lots off gurgling sounds as it shut down. Checked air cleaner for proper installation, checked oil & coolant overflow levels, checked coolant level under pressure cap and found low, started and ran generator with cap off, ran fine, after a few minutes there was lots of spitting through overflow tube and coolant level dropped even further. Bought gallon of ethelyne glycol green coolant 50/50 mix, added apx 1 qt, then ran generator under load apx 30 min, worked as normal, checked & topped off coolant level after cooled down, replaced coolant fill tube in case."

[bigeyes]

Thanks for the replies. As soon as it stops raining here in the Tampa area I will go out and check the generator again for mentioned items.

[caymann]

maybe your fan belt is broken..... check to see if it is blowing air

[tquarles]

I had a similar problem with the 7.5 onan in my Endeavour the day before my warranty expired! Cummins pulled the generator out, pulled the cover off (5+ hours of labor on an '02 endeavour due to really poor design on holiday rambler's part), and changed the temp. sensor(5 minutes of labor) - no more problems. They said that if the temperature sensor fails to register any temp. increase after a minute of operation, it assumes the temperature sensor has failed and wouldn't be able to indicate an overtemp condition, so it shuts down immediately.

[bigeyes]

Thanks for the responses. I'm taking it in to Onan this week and let you all know what the problem is. I believe its the fan belt or the sensor. Too much work for me to handle.

[caymann]

If it is the fan belt, it is major work to take everything out before you can get to the fan belt.
The belt is located in the rear of the generator and you will have to take out all side covers
plus the fan belt protection/wind deflection cover
Use a genuine Onan fan belt (about $50 or so). Alternative belts such as from NAPA that costs a few bucks won't last more than a season and will wear off and you will have to do it again...speaking from experience...

[RollngStones]

Hi - I'm curious if you determined what the cause was. We appear to be having a very similar issue.

[KIX]

To replace the temp sensor on the ONAN 7.5 Quiet Diesel the top cover must be removed. The sensor is at the top of the top, over the fan blade where a coolant hose is connected. It's pretty obvious when you get the top cover off.