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Old 08-09-2019, 09:52 AM   #21
Hacksaw
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Default Re: ONAN Marquis Gold 7000 Gas

I think a valuable lesson can be learned here. Because most large coach style gensets are such an animal to r & r from the coach, it would be wise to take the extra time to test before you reinstall. Now a guy like Rich is set up for this and he routinely does this probably because he has been thru this problem before.
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Old 08-17-2019, 09:58 PM   #22
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Smile Re: ONAN Marquis Gold 7000 Gas

I agree completely. While I don't have a way to load test the unit. Before I installed it the second time, I hooked up a fuel line and a battery and started it to make sure it was going to run. Yes, I should've done that the first time, but I was "certain" I had everything right..........LOL
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Old 09-07-2019, 11:30 AM   #23
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Default Re: ONAN Marquis Gold 7000 Gas

I wanted to give everyone an update on the generator repairs. Went to Bowling Green, then INDY. Genset worked perfectly. I adjust the governor for 62 Hz, no load, and everything worked like new. Thanks to Rich and all who made comments. Looking forward to another 7500+ more hours.
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Old 09-07-2019, 07:00 PM   #24
Rich Biebel
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Default Re: ONAN Marquis Gold 7000 Gas

Yesterday I spent 2-3 hours working on a commercial van with an Onan 7KW gas generator just to make a diagnosis on what was wrong.

I always say there is nothing I haven't seen but yesterday was a new one.

Power in the van would out of nowhere go off or erratically drop.

Generator never gave any indication it was the problem.

Van had a Automatic Transfer Switch and one very common in RV's

AC power in that switch from the generator was never lost going by my Fluke Meter....

The ATS was mounted in a difficult to get at location and after some time I felt like it was the issue...I bypasses it by connecting the generator output straight thru to the load side that fed a breaker panel. Easy to do right in the switch. Would order one and replace it at a later time...

That was the plan....but no....

The problem got worse and now the generator was shutting down and triggering codes.....???

I rechecked my connections and nothing was wrong....

Now I start to think it is the generator itself and that is exactly what was wrong...

The Control board is also the voltage regulator and even though voltage always showed up on my Fluke meter.....once any kind of load was applied AC output would fade.

I swapped in a test Control board and problem was gone. Old board had obvious issues that caused potting material to overheat and melt...

That was the first time I had ever seen a behavior like this one and shows how easy it can be to really chase a problem with a generator in a motorhome/trailer or any vehicle with the added equipment connected down stream from the generator.....
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Old 09-13-2019, 10:58 AM   #25
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Default Re: ONAN Marquis Gold 7000 Gas

Thanks for the story. I like to hear everything that may help me to diagnose a problem in the future. AC (especially 3-phase) can send you in circles troubleshooting. I just had this kind of experience with a customer's submersible pump in a 10K diesel tank.
Thanks again for sharing your knowledge with us.
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Old 09-14-2019, 02:51 PM   #26
Rod Greene
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Default Re: ONAN Marquis Gold 7000 Gas

This is off topic but about generators. I read on here all the time of guys having problems with their ONAN gens. A friend has an Onan and has changed that board many times. If you were building a coach is there a diesel gen that is reliable?
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Old 09-15-2019, 11:25 AM   #27
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Default Re: ONAN Marquis Gold 7000 Gas

Powertech makes reasonably good diesel units.

I have repaired a number of them and they have issues at times just like Onan's

Onan gets a bad rep but to be honest nobody makes anything better...

Powertech generator ends are mostly import built units. The engines are Perkins or Kubota. They use a common controller that can be adapted to most any engine.....and build their own units...

The Powertechs with brushes will usually fail by 5000hrs and the unit will have to come out to repair...and sometimes is more than just brushes...and they use a separate voltage regulator...

I have serviced and repaired many Onan's with well over 5000 hrs on gas units and as high as nearly 10,000 and 10,000 on diesels....

I service 2 medical exam buses regularly with Onan 10 or 12 kw diesels and they use them constantly and their only issue has been water pump belt failures and more than once. My best guess is it is from the diesel engine vibrations thru the balancer and drive pulley causing the belts to fail.

The control board issue is really one that creates a large number of problems and it really should not be but it is. Boards are made in China and say it right on the box....There is one other supplier for control boards and voltage regulators as well as other controls and I have used them a number of times. They make some items that Onan no longer sells and their prices are somewhat lower.....

The control board issue is common in all Onans, gas or diesel...It is a single unit that controls the engine, does shutdowns and controls output voltage....all one unit...

I have one on my to do calendar starting tomorrow....a 5.5 diesel that has had 3 board failures in about 2-3 years.....
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Old 09-15-2019, 11:35 AM   #28
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Default Re: ONAN Marquis Gold 7000 Gas

I have a 10kw diesel that has the belt issue. 500 hours is the max I have gotten. O-no dealer says it should 1000. Have used O-nos way overpriced belt and Gates and Dayco- very similar results. I believe the belts fail because the air flows thru the radiator then over the hot engine before it reaches the belt. I think this very hot air flowing over the belt causes the failures. I have installed an extra fan blowing air into the radiator to hopefully reduce the temperature of the air flowing across the belt.
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Old 09-15-2019, 12:45 PM   #29
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Default Re: ONAN Marquis Gold 7000 Gas

The belt arrangement has not changed much on the 10's and 12's for years. The radiator was always down below the generator barrel end. They use an engine driven fan arrangement to move the air inside the machine....Draws air up and in across the radiator and blows hot air out the other end and below....

The newer machines for some reason have had belts fail prematurely

The older machines did not have the failures for many hours and had the same basic design. The fan arrangement was changed a little but still similar....

7.5 diesels also lose W/P belts but usually from age....many years old no matter how many hours...

The hot air exhaust end of the machine needs to have the proper opening in the compartment....and the air needs to be prevented from being blown into the generator compartment.

I recently installed a replacement 12.5 and had to fabricate a piece of metal to block that hot air from just getting blown inside the compartment.....I also cut the floor of the box out more to better allow the hot air to escape....The machine I replaced had 10,000 and had issues at races down south when it was very hot....possibly the added heat getting in the compartment causing trouble...

I changed a belt on a 10 not to long ago...in a food truck and it was changed once before not long after it was new.

One of the medical buses has had at least 2 belts and the other one has had none done. One machine has at least 5000hrs and the other probably 3000
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Old 09-15-2019, 05:33 PM   #30
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Default Re: ONAN Marquis Gold 7000 Gas

I had one Onan 7K that I installed a deflector shield, on the exhaust side, to direct the air away from the generator. The exhaust air was bouncing of the ground and would be sucked back into the intake side. After that the generator ran great. I also use a fan to make sure the wind at the track isn't blowing the hot air back under the generator.
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