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Old 08-12-2018, 01:30 PM   #1
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Default ONAN exhaust quieting

Hey all,
I just wanted to post this info about quieting the Onan 2500 propane generator. I recently installed a Cummins resonator to quiet the exhaust, and I've been really impressed with how well it worked.
The resonator (which differs from a muffler in that the exhaust flows straight through, and it therefore doesn't affect the exhaust back pressure) was my attempt to cut down the sharp :edge: of the noise. I really didn't expect it to reduce the overall sound that much, but for $35 in parts and $80 at the welding shop, I figured it was worth the experiment.
Now, I wish I had taken before and after reading with w a decibel meter. The noise is much smoother (which was expected from the resonator) and also about 20% quieter ( which is a pleasant surprise). It is by no means silent, but I feel much less self-conscious about running it in the back of a parking lot on a hot day to keep the dogs cool in the van.

So, here is a part number, and the location I installed the resonator. This is on a 2018 Pleasureway Ascent, so you may have a different exhaust pipe setup.

Rick
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Old 08-12-2018, 03:17 PM   #2
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We did the same. Dropped the sound by about 9 dBa and we are considering adding a second one to see if we can actually make the Onan quieter than the van engine at low idle.
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Old 08-12-2018, 03:21 PM   #3
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Originally Posted by Phoebe3 View Post
we are considering adding a second one to see if we can actually make the Onan quieter than the van engine at low idle.
Interesting. I wonder what would happen if the exhaust pipe were tee'd into two paths through separate resonators and exiting on opposite sides of the vehicle.
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Old 08-12-2018, 04:57 PM   #4
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Anybody else notice that Cummins misspelled "resinator" on their box label?

Anyway, I installed one on our 1999 Xplorer last year and was also amazed at the sound "softening". Didn't measure with a db meter but it is much less intrusive and not nearly as annoying. Very worth while upgrade IMO.

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Old 08-12-2018, 05:43 PM   #5
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Found it on Amazon and several other places online. "Resinator" sounds like a 420-type device.

After I double-check to make sure I have room, I think I'll buy one of these.
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Old 08-12-2018, 05:59 PM   #6
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Interesting. I wonder what would happen if the exhaust pipe were tee'd into two paths through separate resonators and exiting on opposite sides of the vehicle.
That's a really interesting question... I don't know that much about exhaust physics... someone elsewhere suggested that a lot of the noise from these generators comes from their mechanical operation, and silencing the case (insulation?) is a good solution as well.
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Old 08-19-2018, 07:40 PM   #7
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Yes, the mechanicals and fan are noisy too, just like your lawnmower, which is in effect what these small generators are.
You can add insulation but you have to make sure it can still get enough air to cool itself(unless it's water cooled).
The newer portable 4 cycle minigenerators from Honda etc are very quiet.
The vehicle engine is water cooled which allows it to be surrounded w much more insulation as only the radiator needs to be exposed to air. The water in the double layers of steel to trap it in the engine also muffles the mechanical noise, so it's hard to make an air cooled one as quiet in a small space that must allow adequate air circulation.
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Old 08-19-2018, 08:14 PM   #8
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Quote:
Originally Posted by Phoebe3 View Post
We did the same. Dropped the sound by about 9 dBa and we are considering adding a second one to see if we can actually make the Onan quieter than the van engine at low idle.
That I would like to see the results of. Also would like to see the results of splitting the pipe and running one out both sides, or one side and one rear like was suggested above.
Don't know if that would be worth the $$ invested though....??
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Old 08-19-2018, 09:17 PM   #9
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You will get better sound deadening from running mufflers in series and not in parallel. In other words one exhaust pipe with two mufflers in a row.
I tried a parallel system on a riding mower but I did just to look cool so I made dual stacks w two mufflers. It was just as noisy as with one.
However, in series they do multiply the advantage. For instance your catalytic converter on your car acts also as a muffler but it's still noisy(although less than open pipes), but then when another muffler is added behind it it becomes WAAAYYY more quiet.
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Old 08-19-2018, 10:15 PM   #10
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This is likely the same resonator the OP used. It’s still not the quietest but the resonator smooths out the noise to make it much more tolerable. I was able to install it with clamps.

https://youtu.be/gQboSPqKtfE
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