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Old 10-14-2021, 02:18 PM   #1
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Exclamation Why running your Onan monthly is important

I confess, I have been lax regarding the monthly exercising of my Onan 7500 Quiet Diesel Generator on our '04 Journey. I figured if we stopped at a Rest Area and warmed up lunch, that would count. It doesn't! Ours started quitting after a minute of run time with an over heating code, so I finally dropped the damn thing with a motorcycle jack, raised the front of the coach up into the stratosphere, and rolled the Generator into my garage. The Temp sensor did NOT want to come out. I finally froze a chunk of ice 2" in diameter, then used a heat gun on the housing while letting the ice melt down on the sensor, and it finally came out - but not all of it. It was corroded so bad I had to punch the innards down out of the tube where it's mounted. I found a YouTube video about relocating the sensor, and decided to give myself a "plan B." I bought two sensors from Cummins at $40 ea. and mounted one in the cleaned out original location. The Thermostat housing has a round recess that doesn't go through to the coolant, and it is the perfect size to be tapped for a second Sensor, so I installed one there as well, and ran wires from both of them out to the front of the generator and if the #1 sensor quits working, I can just change the wire over to #2. Also put in new belt, thermostat, radiator cap, changed oil and all filters, and now I'm going to do a serious radiator flush. When exercising the Generator, if you don't get it up to operating temperature for a while, the thermostat isn't going to open, and there will be no circulation of the coolant at the location of the Sensor, and it seriously gets gunked up and will fail. Lesson learned!
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Old 10-14-2021, 04:14 PM   #2
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Quote:
Originally Posted by corprimo View Post
I confess, I have been lax regarding the monthly exercising of my Onan 7500 Quiet Diesel Generator on our '04 Journey. I figured if we stopped at a Rest Area and warmed up lunch, that would count. It doesn't! Ours started quitting after a minute of run time with an over heating code, so I finally dropped the damn thing with a motorcycle jack, raised the front of the coach up into the stratosphere, and rolled the Generator into my garage. The Temp sensor did NOT want to come out. I finally froze a chunk of ice 2" in diameter, then used a heat gun on the housing while letting the ice melt down on the sensor, and it finally came out - but not all of it. It was corroded so bad I had to punch the innards down out of the tube where it's mounted. I found a YouTube video about relocating the sensor, and decided to give myself a "plan B." I bought two sensors from Cummins at $40 ea. and mounted one in the cleaned out original location. The Thermostat housing has a round recess that doesn't go through to the coolant, and it is the perfect size to be tapped for a second Sensor, so I installed one there as well, and ran wires from both of them out to the front of the generator and if the #1 sensor quits working, I can just change the wire over to #2. Also put in new belt, thermostat, radiator cap, changed oil and all filters, and now I'm going to do a serious radiator flush. When exercising the Generator, if you don't get it up to operating temperature for a while, the thermostat isn't going to open, and there will be no circulation of the coolant at the location of the Sensor, and it seriously gets gunked up and will fail. Lesson learned!
Thanks for sharing. We also have an 04 Journey, but the 39' version. I never thought about that being a potential problem. How tough is access to the sensor? I generally do whatever maintenance I can self learn.
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Old 10-14-2021, 04:46 PM   #3
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Thanks for the tip! I exercise our genny about 30 minutes each month with both A/C units running.
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Old 10-14-2021, 05:46 PM   #4
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When we were test driving our current coach which was used and 7 years old the tech asked me if i turned the generator off. NOPE. Whenever it ran it would stop shortly after. They changed the carb with no results. This was a small dealer and they took it to an authorized onan service. Cost him $1,200.

every month (well almost) i run the gen for 5min with no load then 20min with both ac's then another 5 min cool down. So far so good for the last 6 yers.
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Old 10-14-2021, 06:28 PM   #5
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Teflon tape or teflon thread sealant will make it a lot easier to get the temperature sensor out the next time.
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Old 10-14-2021, 06:37 PM   #6
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Every 1st of the month, easy to remember.
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Old 10-14-2021, 06:44 PM   #7
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Looks like you added another failure point for coolant leaks. Not trying to be flip, just stating the obvious.
The sensor looks very corroded.
It would be wiser to change the coolant every year to keep the electrolysis in check as coolant has anti corrosive properties and they diminish or become "depleted" after so long
Also a sacrificial anode would help. Usually a piece of zinc, that is bolted to the engine , but better yet ,immersed in the coolant .

just sayin
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Old 10-14-2021, 07:47 PM   #8
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Not that it will make much of a big deal, but you now have a temp probe on both sides of the thermostat. So the bottom one will sense the "true" engine temp and the top one is monitoring the thermostatic coolant temp (which will generally be lower). If the thermostat would fail closed, it could take awhile for the engine to shutdown if the top probe is used...
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Old 10-14-2021, 07:52 PM   #9
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Quote:
Originally Posted by OldWEB View Post
Not that it will make much of a big deal, but you now have a temp probe on both sides of the thermostat. So the bottom one will sense the "true" engine temp and the top one is monitoring the thermostatic coolant temp (which will generally be lower). If the thermostat would fail closed, it could take awhile for the engine to shutdown if the top probe is used...
And there is this also ^^^^^^^^

Take out the sensor on the top of the housing. Screw in a sacrificial anode. Done

Well freshen up the coolant too.
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Old 10-14-2021, 07:55 PM   #10
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Not to be negative --- But use it or loose it comes into play- Run those genny's hard a couple times a month or your going to be dealing with issues much worse than the Op did.
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Old 10-14-2021, 07:59 PM   #11
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I'd agree that the coolant was poor and had lost anti corrosion additives . Air trapped at location would add to corrosion but the system has recovery tank. Not sure if coolant needs to changed yearly .
Monthly getting windings baked out is top benefit , probably keep sealed bearings in alternator from pitting as well.
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Old 10-14-2021, 08:07 PM   #12
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Coolant change every 2 years according to Onan. Actually the overflow tank on these is seldom used unless there is an overheat issue- The hose has a 90 deg bend in the cabinet to prevent a discharge of coolant unless over heated.
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Old 10-14-2021, 08:13 PM   #13
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Recommendation is 2 hours/month with 50% load but I know mine hasn't been done because the hours are too low for the age. I live in a very dry climate and store indoors and I am trying to run it at least every couple months for the 2 hours. It's easy in the summer, just run the AC while driving. So far it runs perfect and starts instantly. It will get a lot more use than the previous owners gave it. Air cooled QD 3200.
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Old 10-14-2021, 08:14 PM   #14
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We had an 09 Journey and had a similar problem. The dash ac condensate line was dumping straight onto the sensor causing damage. Cummins installed a new sensor and fabricated a shield to prevent future problems.
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