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Topic: Cummins M11 Turbo Sound (Read 1365 times) previous topic - next topic

Cummins M11 Turbo Sound

While following our motorhome on a recent trip, my wife noticed that when accelerating or climbing a hill, the motorhome made a quite loud sound unlike turbo whistles we'd heard in the past.  It was lower pitched and sounded more like a power tool than a turbo whistle.

The only thing I've heard that sounds similar is some of our city buses make the same sound.  I've never heard anything but the whistle from a diesel semi or pickup.

What is a normal turbo supposed to sound like?
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"

Re: Cummins M11 Turbo Sound

Reply #1 –
A strange sound could be a intake system leak. Hoses or CAC (cold air cooler, inter cooler) would also want to check air filter indicated restriction and visual condition. Better safe than sorry. Cracked exhaust manifold or other leaks make noise too. Can always use a shop vacuum as a low pressure pump on intake and exhaust with engine cold and visually seek leaks. Can also use soapy water (leak detector) too assist. Really hard to describe what is normal sounding with possible different systems. Leaks anywhere are to be suspect and follow were it leads you.
Happy Hunting
Scott

Re: Cummins M11 Turbo Sound

Reply #2 –
Rick,

Do you still have the original muffler on your coach?  If so, it's getting to the age where it could have blown out a hole and changed sound.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Cummins M11 Turbo Sound

Reply #3 –
Quote from: Chuck & Jeannie –
Rick,

Do you still have the original muffler on your coach?  If so, it's getting to the age where it could have blown out a hole and changed sound.

That's what my regular service guy thought.  I now have a new AeroFlow and exhaust piping.  It was a great guess because the old muffler and tailpipe looked like a pile of rotted leaves.  Now, I have great exhaust sound and get lots of compliments, but still have the strange turbo sound.  I LOVE going through underpasses now.

It does sound like you guys think there is a problem and it's supposed to sound like a whistle as the turbo spools up and down?  I'm just not wanting to chase a problem that isn't there.
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"

Re: Cummins M11 Turbo Sound

Reply #4 –
It's difficult for US to remotely diagnose a change in the sound that YOU hear.  You are the expert on what your coach normally sounds like.  All we can do is suggest places on a engine that might contribute to a change in the perceived sound.

Scott (above) made some good suggestions of places to check.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Cummins M11 Turbo Sound

Reply #5 –
Quote from: Chuck & Jeannie –
It's difficult for US to remotely diagnose a change in the sound that YOU hear.  You are the expert on what your coach normally sounds like.  All we can do is suggest places on a engine that might contribute to a change in the perceived sound.

Scott (above) made some good suggestions of places to check.

Agreed.  I'm going to follow Scott's suggestions.  I'll either find something or I won't.  I'll circle back and let you know what I find.  Thanks all.
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"

Re: Cummins M11 Turbo Sound

Reply #6 –
Yup, start by closely inspecting the exhaust system.

Start with the exhaust manifold-- a crack would sure change the tenor of the exhaust.

Check the pipes to and from the muffler as well as the muffler itself.

Also check that the exhaust system and its hangers are tight and not making contact with body or chassis components.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Cummins M11 Turbo Sound

Reply #7 –
 the AeroFlow will definitely have a louder, deeper more mechanical tone and yes anytime there is a wall or underpass or anything that can reflect noise you may hear stuff you never heard, especially if some one is following and hearing it. I would guess most have never heard the noise level in the back of the coach because they are driving, in the front half. That being said using a low pressure air source ("Clean! Clean! Clean! Shop vacuum) doesn't take long to pressure leak check intake and exhaust. spray bottle and couple drops of dishwashing detergent. There will be exhaust leaks, but small bubbles are not to be compared to actual leaks. No leaks in the intake side. Use some foam to upsize fitting into tube leaving air filter housing (assuring not to contaminate intake) and just up the tail pipe. done thousands of times over the years.
Scott

Re: Cummins M11 Turbo Sound

Reply #8 –
Rick, if this is the first time your wife heard the coach after changing exhausts, it might be normal.  The resonator is louder than the muffler.  I have never heard my turbo spool up or down like I hear on a lot of diesels.  Even after I pulled the OEM exhaust and installed a resonator, and punching full throttle through small towns.  Sounds very aggressive, a slight exhaust whistle at idle, but no turbo whine....ever.  A thorough check of your intake/exhaust is still prudent tho.  Woody.
2001 4010 U320 build #5865 "Bluto-d-Bus" since 09/18
2006 Honda Element ESP Toad
Full timing since 2016 in Western MT
Copilot: Sitka
1975 GMC 260 Avion: sold

Re: Cummins M11 Turbo Sound

Reply #9 –
Quote from: dsd –
the AeroFlow will definitely have a louder, deeper more mechanical tone and yes anytime there is a wall or underpass or anything that can reflect noise you may hear stuff you never heard, especially if some one is following and hearing it. I would guess most have never heard the noise level in the back of the coach because they are driving, in the front half. That being said using a low pressure air source ("Clean! Clean! Clean! Shop vacuum) doesn't take long to pressure leak check intake and exhaust. spray bottle and couple drops of dishwashing detergent. There will be exhaust leaks, but small bubbles are not to be compared to actual leaks. No leaks in the intake side. Use some foam to upsize fitting into tube leaving air filter housing (assuring not to contaminate intake) and just up the tail pipe. done thousands of times over the years.
Scott

Ok, cool.  That's even easier than I thought.  I was thinking I'd have to break connections in the middle.  Thanks Scott!
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"

Re: Cummins M11 Turbo Sound

Reply #10 –
Quote from: Pyolet –
Rick, if this is the first time your wife heard the coach after changing exhausts, it might be normal.  The resonator is louder than the muffler.  I have never heard my turbo spool up or down like I hear on a lot of diesels.  Even after I pulled the OEM exhaust and installed a resonator, and punching full throttle through small towns.  Sounds very aggressive, a slight exhaust whistle at idle, but no turbo whine....ever.  A thorough check of your intake/exhaust is still prudent tho.  Woody.

It's not new.  It was there when we drove it home 18 months ago.  The exhaust is probably 8 months old now.  It was there before the resonator and now it's there after the resonator.  The only difference is that I have a very cool resonator. 

Good to know you never hear the turbo spool either. 

It sounds like I now have three things:
1. Normal: A loud, very deep and rumbly, exhaust.
2. Normal: A higher pitched turbo spool that I can't hear.
3. ?: Something else that's making noise, under load, that I need to be able to explain.  Might be normal, but may not be.
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"

Re: Cummins M11 Turbo Sound

Reply #11 –
I had a similar problem/sound on my previous FT with ISL 400 and it turned out to be an exhaust manifold gasket leak. It sounded to me like turbo spooling or idler pulley bearing, but I was wrong . Pulled into a truck stop in Utah and they replaced the exhaust gasket and the sound went away.

Pat

Re: Cummins M11 Turbo Sound

Reply #12 –
Quote from: trailertrashrick –
3. Something else that's making noise, under load, that I need to be able to explain.  Might be normal, but may not be.
If it's #3 then it's worth your time to check it out, using some of the excellent suggestions above.

A exhaust leak, particularly anywhere between the cylinder head and the turbo, can be very destructive.  The extremely hot pressurized gas jet from the leak can melt wiring or hoses, burn insulation, and even possibly start a fire.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Cummins M11 Turbo Sound

Reply #13 –
I just recently thought I had a leak on the turbo, as you described it would make the whistling sound when pulling away from a stop light or under a load or revving the engine. what I found was the belt tensioner on the hydraulic pump (power steering pump) was bad allowing the pulleys to touch making the whistling sound, the spring was broke on the tensioner and would jump over itself when a load was applied you could feel it when taking the belt off, it had good tension and then it would kind of just break over and get easy or have less resistance, it's something that sounds like you might want to check, I sure thought I had a turbo leak. I replaced both the belt tensioners and the belts just to be on the safe side, the belts only had 10K on both of them and they were not stretched. Sound is gone.
Mike & Donna Mariana + Angel & Rusty
2003 U295 3620
Build# 6118
2021 Jeep Wrangler 392

Re: Cummins M11 Turbo Sound

Reply #14 –
Here's a quick audio clip I took out the driver window while punching it through a small town in Colorado in Nov.  No coherent conversations continued at the street side cafe, thats for certain!!!  FYI, it's a Jones Turbine Muffler JT5050XL Resonator.
2001 4010 U320 build #5865 "Bluto-d-Bus" since 09/18
2006 Honda Element ESP Toad
Full timing since 2016 in Western MT
Copilot: Sitka
1975 GMC 260 Avion: sold

Re: Cummins M11 Turbo Sound

Reply #15 –
The verdict, from a heavy diesel truck shop (but not a Foretravel expert), is that the sound is coming from the hydraulic radiator fans and that the sound is "normal".  There was no play in the motors and they were functioning normally.  This explanation kinda makes sense to me as I don't hang out with a lot of people with side radiators, so am not familiar with their normal sound.  I would guess that rear (more common in lower cost diesel pusher rigs) and front (heavy duty truck) radiator fans would be belt driven.

I'll get to listen to more Foretravels as they arrive and depart from the Grandvention.  I paid my deposit last week.

Thanks for all the advice and help.
Rick and Donna
1997 U320 4000 WTBI Build 5152 "Molesley"