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BWilliams's avatar
BWilliams
Explorer
Dec 01, 2017

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?
  • Trackrig wrote:
    Bobby,

    Did you ever get the problem solved?

    Bill

    Don't ya just hate it, when they do that and new member or not, you'd think one would know better?
  • BWilliams wrote:
    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?

    Typical scenario for a bad sensor and those blinking lights give you the code, if you check the manual. You should also have a digital readout for the code on the generator control panel, inside the coach... SENSOR
    Could be an expensive control board, but doubtful.
    I had Cummins replace my supplied part for less than $500.
    You could get some help and drop the genset yourself and did almost go that route myself. The darn thing weighs over 400lbs., the coach must be raised for clearance and then the culprit is in the water jacket at the rear of the kubota engine. They don't always come out easily and usually full of crud, so.....
  • Is the "local guy" an actual Cummins/Onan dealer ?
    If so, I'd think they could do better than that.
    They have always treated me right.

    My wild guess is fuel pump. I have a different model but my pump was intermittent for a while before it failed completely.
  • We have a similar QD8000. Previous owner did not survive it well, and when we bought the coach and then ride to start using the generator. We had some problems to start with:)!

    -Replaced the temp sensor, as the OEM unit had a problem due to incompatible metals, and would fail early.
    -Only 14 months later, 114 outside while in Bishop, CA. Same shutdown, and error code. This time I dug a bit deeper, found out the sensors had a problem, and that a revised replacement part was available. I had conversation with the parts department as I was trying to order the newer 'revised/improved' part number - as they kept insisting that I should use the OEM part number. Amazingly, it took the Cummins Site Manager stepping in to help me (He'd walked by a few times and observed our conversation.). He asked the Parts Manager if it was true that an upgraded replacement part was available. Parts Manager said yes. And the Site Manager said to order me that part, overnight if necessary - and to send all remaining OEM parts back to Cummins the main warehouse.
    -I went ahead and ordered two these, because I have a non slide out generator, so lots of labor hours to drop it out of the front of our coach to work on. The shop I was working with installed one of the new parts normally, I had the second temp sensor metal "C Clamped" to the water line Return manifold. And had these A/B wired in. A = normal location heat sensor. B = C clamped to return manifold heat sensor. (The shop made me sign the invoice that I assume all responsibility for the modification from stock.). So now, once or twice a year, I test that my 'Over Ride B C clamped sensor still works.

    I did this, because I until I knew for sure that the revised heat sensor was going to fix the problem of premature failures, due to the incompatibility of the metals reactions - I wanted a 'back up plan' to keep the generator running. IF it were to shut down, and IF the error code indicate Over Heating. I would check all fluids, and inspect the fan belt was properly working. IF the answer was yes, I'd then switch over to he B C Clamped sensor, and fire generator back up. Due to the B sensor not reacting to the coolant and different metals, it should last forever:)!

    When you are in the high temperatures of the desert areas. Having a 'false error shutdown' of your Generator/Roof Top AC - can really be very uncomfortable, and possibly dangerous to those with medical conditions.

    One last comment. About 2 1/2 years after I did the A/B modification, with the revised Heat Sensor, a buddy of mine had is QD7500 heat sensor go out. He went to a Cummins/Onan shop, and they replaced the sensor (And flushed the generator radiator too.). When he was telling me this, I asked if they used the new improved sensor for the repair. He pulled his receipt, and I compared the part number they had installed to my receipts. His receipt indicated they had installed the OEM sensor... Apparently they're were still using up old stock... This was 6 years ago now, and when I talked with Cummins Northwest about this during a visit. They looked up the old Part Number, and it now shows no longer available...

    SO - OP, if you find you need a new sensor for sure. Good chances you will get the new latest and greatest improvement. I only share this story here, because I was told that the original OEM sensor is still available for sell in Mexico...

    Expensive repair, twice, due to faulty design on a component. The fun of RV ownership!!!

    Best to all,
    Smitty
  • newman fulltimer wrote:
    sounds to me like your choke setting needs adjusted you have it set more for a cold setting


    It is an Onan quiet diesel generator....fuel injected, no choke.

    To the OP, if your generator is mounted on a slide tray, can you move it forward enough to remove the top of the enclosure? If so, you can get to that temp sensor to R&R.
  • sounds to me like your choke setting needs adjusted you have it set more for a cold setting