Onan QD 7500 Generator Mystery

Hello.

So, I have a 2006 Fleetwood Revolution LE with the Onan QD 7500 Generator.

Last winter, last trip out the generator would start, run for 5 minutes and then shut off. It would start right back up and then run for 5 more minutes and shut off. Come to find out it was overheating due to the belt coming apart.

So, over the summer I took it in to have the COMPLETE Onan recommended service done as it hit 1k hours and figured it was best to do it all while it was already removed from the coach.

Fast forward to last week, the family and I were out camping in the desert over T-Day week, which was very warm (90 degrees most of the week). The first couple of days the generator was used 8-10 hours per day to run the A/C's and work perfectly.

On the morning of the 3rd day I fired up the generator at about 10am and it ran for about 5 minutes and shut off. I thought there may have been too much draw as the batteries were pretty low and both A/C's were turned on. I turned off the A/C's and turned down the charger to only charge at 20% and restarted the generator. Once again it only ran for 5 minutes and shut down. I then went out and checked the oil and coolant, which both were good. I turned off the breaker on the generator and restarted it. Same deal, 5 minutes or so it turned off. I then crawled underneath the coach and looked to make sure nothing was blocking airflow, in which it was clear.

Went back inside the coach, grabbed the iPad and started searching around. I came across several threads about issues, but seemed to have covered the basics. The code was (3) blinking lights, which of course can be anything.

So we went on with our day, which was away from camp for most of the day and returned in the evening about dark and for kicks I tried starting the generator once again. It fired right up and before I knew it was about 30 minutes later and it was still running. I turned the breaker back on, turned the A/C's back on and charger to 50% and it stayed running until I shut it off about midnight. The next morning, about 9am I fired it back up and was back to 5 minute run times. I went on with our day as the prior day and waited until it got dark, about 6pm, and tried starting it up once again. Low an behold it stayed running again until midnight or so.

Guess what, the next morning when I went to fire it up we were back to the 5 minute run times....


So, looking over the repair order the only item NOT replaced with a new part was the Water Temp Sender, Part # 193-0318. I can see how this could be the culprit as the ambient outside temperature at 10am was about the same as the ambient outside temperature at 6pm.

I called Onan yesterday and the tech guy I spoke with was clueless and just recommended that I take it in for service to get checked out. The dealer I had do the major service on it it about 300 miles away and the local guy wants $800 for labor to just to pull it out and then diagnose it.

Lastly, the weather here in SoCal has cooled off drastically this week. The highs at my home have been in the 60's, similar to those at night in the desert last week. I had my wife start the generator multiple times this week during different hours of the day and it fires right up and runs for hours.

Any thoughts or recommendations?

You are referring to a "dealer" doing the service work,, is this "dealer" a Cummings shop? or an RV "dealer"? >>>Dan

Most likely you are encountering a coolant sensor fault, fault code 3-24.  If the temp sensor fails to report a change in temperature after 5 minutes of run time, the Onan QD 7500 will shut down rather than risk a no cooling issue and major damage. However, the most common reason for seeing this fault is either a failed sensor or flaky wiring harness.

You need to view the stored fault code when it shuts down - see your Onan manual under Troubleshooting. You can also display the most recent stored code. If it's a 3-24, start diagnosing that sensor. If something else, proceed as the fault indicates.

The coolant sender is a PITA to get at, even on a rig with a slide-out genset (I've helped changed one!). If yours has to be dropped to get at it, iot's gonna be expensive.

I had the sensor replaced on my coach, had to have generator removed , while it's out I had the belt replaced and full service, the sensor on mine was fused to the housing.
Cost was 1600.00

Yeah, when those temp sensors fail, they often get fused to the housing and/or break into a couple pieces that have to be fished out. A real pain!

Front mounted generators that lack a slide-out for maintenance access is another of those shortcomings of lower priced rigs that inexperienced  buyers mostly overlook (until it's too late). A genset slide-out adds substantially to the cost of the rig, so generally found on upper price tier models.

I dropped mine out 8.5 years ago,, had to raise the front of the coach 44 inches above normal resting height,,then used a pallet jack to roll it out from under and a cherry picker to load it on my pick-up.. Reverse all that to install.>>>Dan

Replace fuel pump!