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Old 03-02-2016, 05:53 PM   #1
Join Date: May 2015
Location: Bremerton, WA
Posts: 53
Onan QD 7500 Maintenance Recommendation

Notwithstanding guidance of 1000 hrs for a belt change on the subject GenSet, while performing oil and filter changes at 850 hrs, I decided to remove the closures (top, front, rear) and inspect the coolant pump belt.
As the attached picture shows (note cracks at index finger), I'm happy that I did the 2 hr job at home to avoid the genset shutdown that accompanies belt pieces in the drop down filter access cavity on the road. My coach is 10 years old, and records indicate no previous belt replacement. Based on the deteriorated condition of the belt (cracks thru the rubber to the belt cord every 1/4 - 1/2") I recommend a belt replacement every 5 years or 1000 hrs, which ever comes first.
A couple comments on the job - an air wrench works great for the 40 or so closure bolts. An impact wrench works great to remove the 4 pulley 10 mm bolts (with a new belt in place, holding the crankshaft bolt permits torquing the pulley bolts). Placing the pulley over the pump flange, then pulling the belt over the pump pulley by turning the crankshaft seems to be the easiest belt install method. The OEM Onan part number of ONA-511-0187 has changed to Cummins Part # 0511-0235, and runs about $15.00 from various internet vendors ($26.00 total for 2nd day Priority Mail).
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Old 03-02-2016, 05:58 PM   #2
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American Coach Owners Club
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Great Job as they are often over looked, My only caution would be using an Impacted Wrench on those little 10 mm bolts.

Brownsburg Indiana
1992 American Eagle-8.3C-450hp
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Old 03-04-2016, 02:21 PM   #3
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DHSHULTZ, I second the maintenance recommendation for the Onan.

A week or so before we were due to leave for the Desert Rat Rally I noticed a small amount of coolant leaking from the generator area; and not having the time to mess with it myself had the mechanic at my local indoor storage facility take a look at it. He found that it was only a crack in the expansion reservoir; that was the good news. But he also noted that the generator had a little over 800 hours on it and wondered as long he had it unbuttoned if I wanted him to do the 1000 hour inspection (Huh, 1000 hour inspection?) and service. That all sounded like a pretty good plan to me, I just wanted to get the show on the road and head for the desert.

There are quite a few items that need attention at the 1000 hour point, and yes changing out the belt is one of those items. My belt looked pretty much the same as yours if not worse. This is definitely an item everyone should think about replacing, if not for hours of use, but years in service. One of our ACA members at the Quartzsite rally had his belt fail, and changing it in the desert is not the most convenient place to do that job. Besides the belt replacement it is also suggested to replace the water pump, a multitude of hoses of various diameters, some of which are pre-formed and others straight, thermostat, radiator cap, new coolant, and a few other minor items.

For the most part our generators are trouble free and we pretty much take it for granted that every time we push the start button it will always perform as expected and continue to do so for hundreds of hours. But, we should also keep in mind that besides the regular oil and filter changes there are quite a few other items that will require occasional attention from time to time.
2006 Alpine 36' FDTS
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Old 03-04-2016, 02:54 PM   #4
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Location: Over the next hill, around the next curve...
Posts: 3,500
Not sure if it is the same on the QD7500, but on the QD8000 the Temperature Sensor is known to go out and result in a 333 error code, running hot... In this case, the generator is not actually running hot, but when the sensor goes out, it comes the connection to the brain which looks to it as if the sensor is sending a High Temp.

We replaced ours twice. The last time, we had a second temp sensor A/B switched into the mix. With the secondary sensor hose clamped to the mental intake of the hot water return into the generator.

So this way, if the OEM placed Temp Sensor again fails. I can validate that fluids are in good shape, check the belt is good, and oil levels are also OK. If so, I will then switch over to the alternate Temp Sensor, allowing continued use of the generator. Yeah, I'll replace the OEM located Temp Sensor again too, but on my schedule - as opposed to running up Highway 395 and having the generator shut down in Bishop with 112 degree bank temperature flashing down at us!

If any of you do this, please note that you are assuming the risks, and you also should do regular checking of all vitals while using the alternate temp sensor. (I have not had to use this yet! But, I do test it about every three months, to be sure the "B" alternate Temp Sensor still is working too.)

And another common problem with these units, is neglecting of testing the coolant, and keeping the smaller radiators cleaned. We had to replace our generators radiator, even flushing would not get it unclogged. (Bad maintenance from previous owner.) We had Final Charge OAT based coolant added to the generator radiator, same as we run in the coach, for ease of carrying only one kind of spare coolant. The bonus, is I feel the generator is running a bit cooler then it had on regular coolant.

Best to all,
Roo II is our 04 Country Coach Allure 40'
OnDRoad for The JRNY! Enjoy life...
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maintenance, onan

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