Onan 5500 Generator

[Miramar Owner]

After having issues with my generator last fall I decided to take it in for a thorough tune up at a certified Onan repair facility. I picked it up yesterday after spending $2,400 for the complete tune up, included setting the valves, replacing fuel pump and all filters, replacing spark plugs and changing the oil.

Today it purred like a kitten while under load with the AC running. Once I turned off the AC, it began to idle rough and blow out a puff of smoke. Then idle smoothly for another minute...idle rough and puff again. It continued that cycle for about 15 minutes until I finally shut it down.

Back to the shop again next week. In the meantime, does anyone have any thoughts on this? It was last gassed up in October...can older gas be a factor?

[The Gritz Carlton]

How did it run at the shop after all the repairs, before you paid. Surely they tested it for you, no?

[16ACE27]

Originally Posted by Miramar Owner

After having issues with my generator last fall I decided to take it in for a thorough tune up at a certified Onan repair facility. I picked it up yesterday after spending $2,400 for the complete tune up, included setting the valves, replacing fuel pump and all filters, replacing spark plugs and changing the oil.

Today it purred like a kitten while under load with the AC running. Once I turned off the AC, it began to idle rough and blow out a puff of smoke. Then idle smoothly for another minute...idle rough and puff again. It continued that cycle for about 15 minutes until I finally shut it down.

Back to the shop again next week. In the meantime, does anyone have any thoughts on this? It was last gassed up in October...can older gas be a factor?

Generators like the Onan 4K or 5500 don't idle. They run at the same speed all the time. The throttle is opened/closed to maintain that speed when the electrical load increases/decreases.

So if your Onan is slowing down to an idle you have bigger problems.

[Miramar Owner]

Originally Posted by 16ACE27

Generators like the Onan 4K or 5500 don't idle. They run at the same speed all the time. The throttle is opened/closed to maintain that speed when the electrical load increases/decreases.

So if your Onan is slowing down to an idle you have bigger problems.

Maybe I misspoke using the term "idle". It ran perfectly under load then would run rough, throw out a puff of smoke...then run perfectly again for another minute and start the cycle all over again.

They remove the generator from the RV to set the valves and ran it for 5 hours with no issues. They put it back into the coach and ran it for a few minutes just make make sure everything was properly connected.

I'm wondering if something inside the generator compartment is not allowing it to vent properly. It ran extremely hot.

[16ACE27]

Originally Posted by Miramar Owner

Maybe I misspoke using the term "idle". It ran perfectly under load then would run rough, throw out a puff of smoke...then run perfectly again for another minute and start the cycle all over again.

They remove the generator from the RV to set the valves and ran it for 5 hours with no issues. They put it back into the coach and ran it for a few minutes just make make sure everything was properly connected.

I'm wondering if something inside the generator compartment is not allowing it to vent properly. It ran extremely hot.

Or it has a fuel problem from the RV tank.

[Miramar Owner]

[QUOTE=16ACE27;381615]Or it has a fuel problem from the RV tank.[/QUOTI


I'm hopeful that is the problem. I'm going on a trip with it this weekend and will run the fuel tank down below half before filling up. Normally I add Sta-Bil on my last fill up before parking for the winter but I failed to do that this time. I'm uncertain if that could even cause the problem. I have an appointment to take it back in next week. If by some miracle adding fresh fuel solves it, I will cancel.

[MJC62]

Quote --------- "Normally I add Sta-Bil on my last fill up before parking for the winter but I failed to do that this time. I'm uncertain if that could even cause the problem."---------------
IMO you are on the right track. Old/stale gas has lost a good portion of its combustibility. Stored without a fuel preservative the gas in your MH's tank may have lost 3-4 octane over the time in of storage. In addition, the alcohol in the gas will absorb water.
If it were my motorhome, I would dump some octane booster into the tank before I drove it.

[Miramar Owner]

Originally Posted by MJC62

Quote --------- "Normally I add Sta-Bil on my last fill up before parking for the winter but I failed to do that this time. I'm uncertain if that could even cause the problem."---------------
IMO you are on the right track. Old/stale gas has lost a good portion of its combustibility. Stored without a fuel preservative the gas in your MH's tank may have lost 3-4 octane over the time in of storage. In addition, the alcohol in the gas will absorb water.
If it were my motorhome, I would dump some octane booster into the tank before I drove it.

It definitely won't hurt anything so it's worth a try. I'll keep you posted.

[Chateau_Nomad]

I had that happen to a snow blower. I had just bought fresh gasoline (BP) to fill the tank. Would fire, but would not start and run.

Took it to the local mower shop I always used the next day. First question... Where did I buy the gas?

I stood there and watched the guy dump the gas and put in fresh Sunoco gas. Fired up first pull. Ohio is a dumping ground state for poor gasoline. That particular BP station was notorious for junk gas. Lesson learned.

[Mulerider]

That's hard to believe $2400. A valve job on 5500 should run about $300, fuel pump cost $25, spark plugs and oil change. You don't need a valve job until 500 hours or if you're heating a ticking nose. Plus a brand new 5500 onan is $5100. Hourly rates range from $75 to $125. At $125 an hour they worked close to 19 hours. Something seems a little off. It should only take 5 hours to remove and replace.

[Miramar Owner]

Originally Posted by Mulerider

That's hard to believe $2400. A valve job on 5500 should run about $300, fuel pump cost $25, spark plugs and oil change. You don't need a valve job until 500 hours or if you're heating a ticking nose. Plus a brand new 5500 onan is $5100. Hourly rates range from $75 to $125. At $125 an hour they worked close to 19 hours. Something seems a little off. It should only take 5 hours to remove and replace.

I could send a photo but it is what it is. Onan techs aren't cheap. I took it in with issues and it was $220 just to diagnose.

[Mulerider]

Oh, wow! Well, at least they should make it right. I found a rv mechanic in vail az near us. He has worked in the field for 36 years and now works out of his home. He was tired of working for dealers and seeing how they rip people off. Very knowledgeable and reasonable.

[CactusJuice]

Did they clean/replace the carb for the $2500? A dirty carb is certainly what this sounds like based on my years of experience with carb issues on small engines. A new carb is a couple hundred bucks from Cummins and much cheaper from other sources.

[Miramar Owner]

Originally Posted by CactusJuice

Did they clean/replace the carb for the $2500? A dirty carb is certainly what this sounds like based on my years of experience with carb issues on small engines. A new carb is a couple hundred bucks from Cummins and much cheaper from other sources.

Yes... The replaced the carburetor... It took 3 weeks to get it. They pretty much went thru everything and when I left they assured me out would run like a new one.

I think I mentioned they ran out outside the RV for 5 hours to test it. That's why I'm thinking it's either bad gas or something blocking air flow making it run excessively not.

[Jimbo56]

Put 4 cans of Seafoam in your gas tank. Fill up with gas & drive around a bit. Then fire up the generator and let it run, under AC load, for a couple of hours.

[ducksface]

I'm having a really hard time believing valve job is a 500 hour thing.
5,000 maybe.

500 hours is
35mph on a city bike with a similar engine is
17,500 miles.

Unacceptable.

And
My onan did the same as the op's, almost exactly.
The throttle butterfly broke off and flung the pivot rod and screws into the combustion chamber, the pivot holding a valve open as the exhaust tried to spit it out.
Extended warranty, $100 deductible. Covered.

$190 diagnosis. $190 an hour. They owe me $90 back.

And
It's 8 easy to get to bolts, a clamp on the exhaust pipe, an electric plug and a gas line. 90 minutes to pull one if you've never done it before. 45 minutes tops tops tops if experienced.

And

While it's out, do this;
https://www.thorforums.com/forums/sh...postcount=1309

And
Any small engine repair shop would have had a carb in two days And charged you 1/3.
Your authorized place is a bunch of clowns for that carb not being in stock.

[Miramar Owner]

Just a quick update...
I removed the panel on the bottom of the generator and found the fan packed full of mouse bedding. I thoroughly cleaned it all out, remounted the plate and started the generator. It ran perfectly until I finally shut it off after an hour. Problem solved. If you ever have a generator run hot, that is the first thing I would check.

[16ACE27]

Originally Posted by Miramar Owner

Just a quick update...
I removed the panel on the bottom of the generator and found the fan packed full of mouse bedding. I thoroughly cleaned it all out, remounted the plate and started the generator. It ran perfectly until I finally shut it off after an hour. Problem solved. If you ever have a generator run hot, that is the first thing I would check.

So was it packed before? Or after your $2400 service?

[Miramar Owner]

Originally Posted by 16ACE27

So was it packed before? Or after your $2400 service?

The service was needed but most likely caused by the generator getting excessively hot. That panel is not removed when the generator is removed from the coach. It basically protects the bottom of the generator. When the generator is sitting outside the coach it will operate fine. Once reinstalled into the coach, the debris pack will cause excessive heat build up when it's ran for more than 30 minutes or so.

My problem is I only run the generator annually over Labor Day when we're dry camping at an event. Otherwise, I run it in the winter just to exercise it, sucking the debris tighter into the fan.

Bottom line is the debris was there when I took it in but that plate is not removed to replace plugs, fuel pump, Fuel filter, set valves, replace carburator or change the oil. It now runs like new and I know how to prevent the issue in the future.

[Jimbo56]

I guess that’s the sorry state of affairs in our country. $2400 to service it and they never found/saw/looked for a cooling blockage.