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Old 01-10-2018, 12:14 AM   #1
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"Shhhh" sound from engine; turbo?

(Not sure if this belongs here or Freightliner Chassis or another board..)

Today we took the road for a 200mi trip with our Thor Aria (ISB 6.7 Cummins on a Freightliner chassis) and discovered that now when the engine is under load we hear a loud "Shhhhhhhhhhh" noise coming from the rear. On our previous trip four days ago there was no such noise.

From the driver seat, the noise really sounds like someone is bleeding air from a tire. After a bit of panic I put the "Turbo Pressure" metric on the dash display and it looks like the noise is directly correlated with turbo pressure: nothing to be heard at 0 PSI, it exists at 10 PSI, it's definitely there at 20 PSI and it's loud at 28 PSI. Everything seems to be behaving like normal otherwise. The engine has 13K miles on it.

Does this sound familiar? Something obvious I should look at? (Note: I haven't had a chance to poke around the engine since we landed tonight, will try to visually inspect tomorrow).

Vince.
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Old 01-10-2018, 03:11 AM   #2
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Quote:
Originally Posted by vmallet View Post
(Not sure if this belongs here or Freightliner Chassis or another board..)

Today we took the road for a 200mi trip with our Thor Aria (ISB 6.7 Cummins on a Freightliner chassis) and discovered that now when the engine is under load we hear a loud "Shhhhhhhhhhh" noise coming from the rear. On our previous trip four days ago there was no such noise.

From the driver seat, the noise really sounds like someone is bleeding air from a tire. After a bit of panic I put the "Turbo Pressure" metric on the dash display and it looks like the noise is directly correlated with turbo pressure: nothing to be heard at 0 PSI, it exists at 10 PSI, it's definitely there at 20 PSI and it's loud at 28 PSI. Everything seems to be behaving like normal otherwise. The engine has 13K miles on it.

Does this sound familiar? Something obvious I should look at? (Note: I haven't had a chance to poke around the engine since we landed tonight, will try to visually inspect tomorrow).

Vince.
You have a charge air leak.

So it could be a busted hose if you are lucky.

Could be the charge air cooler itself (expensive).

To find out exactly where the air is leaking from you will need assistance.

To do this, have the assistant stand next to the coach with the engine access cover open, while you place the coach in gear, with parking brakes applied.


You then load the engine by holding your brakes and pressing the accelerator no more than half way for ten to fifteen seconds.

Place the transmission in neutral to cool, and consult with assistant as to where the air is escaping.

You may have to do this a few times to pinpoint the exact location of the leak.
You will not hurt the transmission with this method as long as you are observing the load times, and cool down period Iíve noted.

As far as how close your assistant has to get to the engine during this test is dependent on your comfort factor and the safety of all involved.

Good luck and please provide an updated on your findings.

DTW
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Old 01-10-2018, 05:03 AM   #3
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The charge air cooler looks like a radiator and is mounted with it. The pipes to it are often aluminum, about 3" diameter, with short red or blue connector hoses going to it.
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Old 01-10-2018, 09:14 AM   #4
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Well,
It's possible he's got a charge air leak but, with 28 psi on the gauge, it can't be much and, being as loud as it is AND, having 28 psi, I'm wondering but, surely I'm not an expert at this. And, it does sound like maybe a thorough inspection is in order of the turbo system. Could it be the air INTAKE system too? But, the fact that the OP says this condition is new and hasn't been there before.
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Old 01-10-2018, 09:21 AM   #5
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Hopefully it will be a loose clamp.
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Old 01-10-2018, 10:34 AM   #6
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If you look at the piping going to the charge air cooler there will be connecting hoses. They have clamps on each end and they will sometimes come loose or break. Also the hoses sometimes split. I would bet it will be a clamp that is not positioned right and has come loose. Also look at the exhaust manifold they sometimes crack and will cause that noise.
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Old 01-10-2018, 11:47 AM   #7
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Thank you for the various inputs. I did a visual inspection today with the engine at rest to try to find something obvious (loose clamp or crack somewhere) but nothing jumped at my untrained eye. I tried to wiggle the hoses/clamps that go from the turbo to the cooler and from the cooler to the intake and things looked sturdy enough (again, to my untrained eye...)

I am hoping to try the running test DTW suggested tomorrow when it is time for us to break camp again, I imagine putting the coach in gear (even with the breaks fully applied) is probably not the best idea with the jacks down and the slides out...

And just to make sure I am looking at the right things, could you confirm my understanding of what's what? Below are two pictures taken from underneath the coach looking up, front of the coach is left, rear is right:
1- exhaust coming out of turbo and into exhaust system
2- charge air coming out of turbo
3- fresh air coming into turbo from air filter

Vince.
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Old 01-10-2018, 11:57 AM   #8
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...and another question: we are on our way back to California from TX and have another 1,800mi ahead of us with a few stops here and there. Is it reasonable to wait until we are home to have it worked on while it's easy and the cats are out of the rig and drive with the leak or should I change all our plans and do what I can to find help ASAP? (nearest Freightliner center on our route is in ~500mi in El Paso).

I know the description of the problem is not a lot of information to work with though..

Vince.
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Old 01-10-2018, 12:03 PM   #9
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If there is a possibility of an air leak between the air filter and engine intake, I would not be driving it.
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Old 01-10-2018, 12:22 PM   #10
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Bottom pic. #2

Hose looks like it should be pushed further on to the turbo. Up to the "nub"

Loosen clamp and try to push further on.
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Old 01-10-2018, 12:26 PM   #11
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Well, your description seems to be related to the pressure side of the turbo/intake system. If it is related to boost pressure, and you have no loss of power under load, it is likely a small leak, and may be near the intake manifold. If you can look on the intake side of the engine, it may be a coupling has come partly off. It could go on like this for quite some time, or if it gets worse, you will have big loss of power, pulling grades, accelerating, etc. If it does get worse, and you can put up with the loss of power, it shouldn't cause any engine problems. Maybe someone else had heard of engine damage for boost loss, but I have not.


Good luck and please get back to us with what you find.
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Old 01-10-2018, 12:28 PM   #12
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Is your turbo whistling at all while your engine idles, or is it totally quiet? That should give you a REAL good hint as to if you have an intake leak. Is your engine intercooled? I'm ASSUMING it is from the piping around your turbo, but better to be safe...

If nothing else, tie a piece of tissue to a long stick or screwdriver, then with the engine running, slowly wave the tissue around the air cleaner to turbo piping, and any piping coming from the turbo to intercooler and from intercooler to turbo. Any leaks that weren't obvious before will flutter that tissue and show you if you DO have a major intake leak of some kind.

In all honesty, any leak you have there should be blowing out at you pretty earnestly. Unless your radiator is right back there, no fan or other breeze should be coming out. Let us know what you find and good luck.
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Old 01-10-2018, 12:51 PM   #13
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If your only hearing the shhhhh sound under load It could also be just an exhaust leak. A clamp might have let go try following the exhaust seeing how your not loosing any power .Try starting the motor and have someone rev up the engine a couple of times while your near the engine and follow the exhaust pipe. Hope it's an easy fix.
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Old 01-10-2018, 04:00 PM   #14
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X2 on an exhaust leak.

We had the exact same symptoms on a Cummins ISL...a loud hissing sound whenever I was in the throttle. It turned out to be a cracked exhaust manifold.
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