ONAN Marquis Gold 7000 Gas
 

I am at the Topeka double.
After running great all week in Denver, my generator won’t
stay running when I let off the start button. The light on the button just flashes
while it runs. No 120V is being produced. I believe that it must produce AC
to keep running. No codes are showing on the Start button, but I have a control module from Flight Systems, and I think they don’t send out as many trouble codes as the ONAN units. Before ordering another control module, is there anything else to check first? Brushes, continuity?
Thanks,
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Rich Biebel is the man on Onans. I can say that I had one that fried the voltage regulator and would only run if the start rocker switch was engagad. Twice. Once because it ran out of fuel and the motor was surging and the other time caused by very slow cranking from a low battery. Hope this helps.

Re: ONAN Marquis Gold 7000 Gas
 

Man, what a place (and time of year) for your gen set to crap out! Sure it's hot as XXX there right now.

Hate to bring bad news, but your main control board is probably toast. At least that was what had happened numerous times to me when I ran gas sets on my work trucks for 30+ years.

Re: ONAN Marquis Gold 7000 Gas
 

Check the brushes first. They wear and can damage the surfaces they make contact on. Slip rings is the name for them. If the brushes are bad and the slip rings need cleaning, a piece of emery or sand paper taped to a paint stir stick cut lengthwise to fit in there works best. Start machine and hold button down or put the machine into ERO mode if it has that option. Engine Run Only mode. Brushes can wear out in 700-1200 hours and occasionally much sooner.

Re: ONAN Marquis Gold 7000 Gas
 

Hi Rich, when I pulled the control board out I checked the brushes. The brushes and slip rings are good. I just received my new board and after installing it the problem is the same. It will only stay running if I hold the start switch down. Tom from Flight Systems
Is going to call at 2P to help troubleshoot the problem.
Thanks for your help.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

I have checked continuity of all of the windings and everything looks good. How is the
engine connected to the generator section? The generator appears to set at a 90 degree angle to the engine. Is there a belt under the unit to connect them?
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Yes there is a belt and if it or the rubber coupler broke, the generators rotor won’t be turning. Pull the brushes and look in there and start it. Rotor should be spinning. Testing would get more involved if it is spinning.

Re: ONAN Marquis Gold 7000 Gas
 

Thanks Rich. I’ll do that tomorrow.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Dan: Not two months ago my 7000 gave me some grief. Started and ran but noisy like it was going to throw a rod and there was a very slight burned rubber smell. Turned out to be the rubber coupler under the engine flywheel that drives the belt to the gen. armature as Rich already mentioned.

Re: ONAN Marquis Gold 7000 Gas
 

I removed the brushes and the slip ring does not turn when the engine runs.
I’m not sure which is broken, the belt or the rubber drive mechanism. I didn’t smell any burning rubber in mine. I will probably replace both since you have to separate the base plate to get to both.
Thanks for all the helpful tips.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

The rubber coupler is bolted to the engines flywheel
and drives the serpentine style belt that drives the rotor in the generator.

The couplers break, belts sometimes break but usually more if they are oil soaked. Oil leaks are pretty common on these units. Oil collects in the plastic cover under the upper tray. Belt gets oily and comes apart.

It’s a pretty big job taking it all apart but I do them pretty regularly.

I know every nut, bolt, wire and everything else in most all Onans.

I have various specialty home made tools to do them and always have the parts on the shelf for fast turnaround.

You found the trouble so at least you know what you have to do now to fix it.

Re: ONAN Marquis Gold 7000 Gas
 

I have ordered the belt and coupler, I have replaced the coil units on a different unit and have had the two halves of the genset apart. I figure that is half the labor to get to the belt. I figure that it's best to replace them both while I'm in there.
I'll post when I get it repaired.
Thanks for the help.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Check the tensioner at it’s bearing and plastic wheel. If it’s noisy or shows wear, replace it too.

Re: ONAN Marquis Gold 7000 Gas
 

Thanks Rich. I will check it too.

Re: ONAN Marquis Gold 7000 Gas
 

I got the generator apart and the belt was shredded. I cleaned (a lot), replaced the engine coupler and belt. The tensioner was good. It’s no small task to put the belt on and move the tensioner far enough away to get the belt on. As Rich stated, there was oil everywhere. Spent most of the time cleaning all of the pieces prior to reassembly. The generator is ready to go back in the trailer, and ready for another 7500 hrs or more.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

I was very happy to get the generator back in the trailer, however, it would not start. It is back-firing through the carb. While I did have the coils unbolted from the engine when I removed the flywheel, I did not take them out. When I put them back on (2 bolts) in their same places, I made sure that I had clearance (probably too much) from the flywheel as it rotated. It sounds like the timing is off but I'm not sure how that could be. I did not set the gap on the coils. I just read the manual and it said to set them at .012". If the gap is too wide, will that cause the back firing through the carb?
Grrrrr.......................
Dan

Re: ONAN Marquis Gold 7000 Gas
 

I removed the generator and reset the air gap for the coils. Now the generator is happy.....but not as happy as I am...........
Dan

Re: ONAN Marquis Gold 7000 Gas
 

The spark timing is fixed. The flywheel is keyed to the crank and has magnet inserts. I set the coil air gap with feeler gauges. They are magneto type coils and the small white wire is to ground them to stop the spark.

I have a sequence for doing the belt and tensioner and it’s pretty easy once you do as many as I have.

I made up some various tools to do these machines.

Flywheel puller plate , chain rig to lift upper section off base.

I pull engines off the base and split the case to replace the base gasket when one fails. Cleaning that mess under the base takes some time and a lot of chemicals. WD-40 works very well and some other solvents and eventually Brakecleen....

Re: ONAN Marquis Gold 7000 Gas
 

There were some blind holes in the upper plate that I tapped for 3/8” eyebolts. I then made some straps to separate the 2 halves. When I removed the coils to remove the flywheel, I put the coils back but the air gap was at the maximum distance allowed by the adjustment in the bolts holes. After I reset the gap to .012” and reassembled the generator, it started and ran fine. Thanks again for the tips.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Did one today. Coupler broke. Pulled machine out yesterday afternoon after reinstalling an old BGE in an old motorhome.
Had it cleaned up and back together and running today by early afternoon.
Load tested it for a while.
Got sidetracked fixing another one with random shutdowns.
Replaced control board on that one.
Rain prevented me from reinstalling first one.
Will complete it tomorrow and then on to a diesel 5.5 and others waiting in the wings.
Pretty much non stop lately.....

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.

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
Dan

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.
Dan

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.....

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.
Dan

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?

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.....

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.

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

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.
Dan

Re: ONAN Marquis Gold 7000 Gas
 

Dan that is exactly what needs to be done but isn’t by just about any builder of motor homes and trailers.

The newest vans with generators installed have sheet metal completely isolating the hot air exhaust side from the cool air inlet area.

It makes a huge difference on how well they run and last.

I see poor installs all the time.

Re: ONAN Marquis Gold 7000 Gas
 

I have an 8 K Onan diesel in my Toter. I live in Florida. When its hot I run a fan to blow the heat out from under the generator.

Re: ONAN Marquis Gold 7000 Gas
 

looking back on the many questions and replies about Onan gens it seems not only Onan but probably many other gens have a lot of problems caused by OVERHEATING. If the gen had a lot of fresh air and wasn't jammed into a compartment WITHOUT sufficient clearance around it to allow the heat to escape this might cause the overheating--- I bet if you put a Onan gen on the ground in direct sunlit on a 100*+day it probably would run until it ran out of fuel with no problems whatsoever---Take that same gen cram it into a confined area with not much air circulation and its a recipe for disaster.
Perhaps a modification to the compartment and/or additional fans blowing LOTS OF COOLER AIR on the gen and to help get some cool air in there or out of there would lessen the chances for failure--MY 2 CENTS -- Mr Biebel care to comment please?--Fed 387

Re: ONAN Marquis Gold 7000 Gas
 

There's alot to be said in that regard, FED. And, I am sure Rich will agree.

We (the mobile tool industry) tried running Honda gen sets in our tool trucks a few years ago and experienced horrible results. Honda engineers ultimately totally agreed that the problems were caused by us putting them in those small compartments where they were subject to too much heat.

While we tax the Onan products by running them so many hours a week in such heat, they are still the best thing going for anyone, or anything, requiring mobile power.

Re: ONAN Marquis Gold 7000 Gas
 

I went through all the same overheating issues with my Onan a few years ago. The main problem is the way the LQ conversion factory installed the generator with very limited ventilation. The intake air and exhaust air not being separated and ducted apart to eliminate recirculation of the heated air. This eventually causes the board to overheat and either shutdown or fail. Another racer informed me last year that Onan makes riser kits to elevate the generator, and has a divider and can pull intake through the front. This solved their overheating issue. It's unfortunate that the trailer manufacturers that install the generators do not follow the recommended clearances for ventilation provided by the generator manufacturers.

Without help from Rich I was ready to give up on a generator that had very little run time and failed every race we went to. I have ducted the exhaust air to discharge to the opposite side of the trailer from the intake air, and we have a box fan that also runs to ventilate the generator compartment.

Page 13

https://mart.cummins.com/imagelibrar...es/0058349.pdf

Re: ONAN Marquis Gold 7000 Gas
 

I have serviced and repaired the 7kw gas units since they redesigned them. Had a long list of mobile dog groomers that came to me regularly. They have vans and the generators were mounted in various places over the years by basically one builder. They build a number of different vehicles and the latest is a Dodge Ram long van with the generator in the back on the floor in a compartment with a door and completely enclosed. The cool air intake is below the floor and the hot air exhaust area is completely isolated with a screw together sheet metal cover. I just serviced the one I point to all the time. 3755 hrs and the young lady takes great care of it. Oil changes and full service as recommended by Onan. It’s 5 years old and like new. Does not get road debris in it and runs as good as one could with that many hours. Serviced another long time customer last week. Older style van with Gen in rear side compartment and on support legs as all of those are. 7750 hours and I’ve repaired it a few times. New cyl heads at 3 or 4 thousand hours. She’s probably my longest dog groomer van customer.
Installs are terrible on many vehicles. The builders never read the install guidelines. Food trucks and sign trucks ....and I’ve seen racer trailers just as bad or worse.

Heat kills these machines, they are AIR cooled !!

Ask Lee and Brian Valentine about their Onan that would shut down last year at MG Div. Race. A new LQ trailer with Gen install by the trailer builder. A fan blowing on the unit kept it going. I gave Lee some suggestions and they made some changes and it’s been ok.

I need to add that no Onan air cooled machine has any specific hi temp shutdown sensor.
They just shutdown from either control board overheating or a vapor lock/ carb issue. The heat also kills the plastic floats in the carb. and you cannot buy any parts for that carb. I replace them often anymore. A Complete carb is all you can get.

Re: ONAN Marquis Gold 7000 Gas
 

Rich--- does any gasoline WITH ETHANOL affect or deteriorate the floats ??? I know on some of my older personal yard stuff it STRONGLY recommends against using gasolines with ethanol or very small amounts of ethanol but preferably NO ethanol ---whats your take on this??? FED 387

Re: ONAN Marquis Gold 7000 Gas
 

The newer machines in the last few years have had odd carburetor problems that I never saw before.

Random issues with stalling. When it gets real bad gas just pours out the carb.

Float appears darker but does not have fuel inside it. It gets heavy and sinks and floods.

Last week I spent a good 2 hours on a machine that would run for a few minutes and just shut off. I chased it changing various components and a new carb fixed it. They have a solenoid on them to shut fuel flow off thru the main jet. The solenoid was causing issues with feedback to the control board.

I always say there is nothing one of these machines can do that I haven't seen......that was a completely new one and the carb issues have been also hard to diagnose.

I lost a customer over that one probably....A girl had repeated issues and no matter what it never failed for me when I tested the machine.

Ethanol creates a gunk different than fuel used to create if it sat. Used to be gummy varnish in reg fuel. Ethanol leaves a greenish, yellow sugary like substance. Both will cause big problems......

My son was/is a motorcycle person since forever. He used an ultrasonic cleaner for carbs...…..I never have seen or used one myself for carbs.

On generators I replace them most of the time.....waste to much time trying to clean an old one and most of the time it takes numerous tries to get it working decent....

Re: ONAN Marquis Gold 7000 Gas
 

On my Honda Generator, I've had success using Av-Gas!
(110 low leaded fuel, cheaper than SEF)

Re: ONAN Marquis Gold 7000 Gas
 

I live in Tulsa and the availability of what is called E0 is quite good for 87 and I use it in my generator, lawn tractor and other small engines.

E0 91 is available but not as easy to find as the 87. We have not had 93 in any form in this area for a long time.

The E0 is often advertised as "Real Gas".