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Discussion Starter · #1 ·
I bought my hx30 used. It had some play in the shaft. (Not much) Anyways, after a couple thousand miles, I hear a whistle. It’s not the normal turbo whistle. This sound is at a constant cruise when the boost is at about 10-12. If I let off, it goes away. If I put my foot in it to make 20 plus boost, it also goes away. It almost sounds like belt squeal, but I have ruled that out.

Would that turbo shaft play make that kind of noise?
 

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I had similar noise once and was convinced my turbo was going to implode. But it got worse with more boost/load.

Turned out I had a loose nut or two holding the turbo on and the leak past the gasket was whistling. Turbo was fine.

Sounds like you've got a harmonic somewhere or something is fluttering. A turbo that's going to die usually doesn't give you any warning. I've only had that once. It gave an EGT spike first, then rumble and then dropped all boost. About 2 seconds from okay to not-okay.
That turbo was damaged from a prior oil line failure (same piece of road exactly a week earlier). I put a rebuild kit through it and it's still going fine 15 years later.
 

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Discussion Starter · #3 ·
I’m wondering if it could be a water pump. Does a water pump ever make noise without leaking? The other possibility is the tensioner pulley. I recently change the configuration of my belt and used an old tensioner I got off eBay. Maybe the bearings are going. Today, when I was driving around, the noise went off and on with no rime or reason. (Mostly on)
 

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a bearing giving out sounds like a good call to me, I'd remove the belt and then rotate each pulley by hand one that is on the way out will have a distinct feel if not a sound a mechanics stethoscope could be used while it's running to localize the issue if you have one.
 

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Discussion Starter · #5 ·
So I pulled the belt and everything turned nice but the water pump. It didn’t feel rough, but it would turn easy for a 1/4 turn and then turn harder for a 1/4 turn. Kind of felt like turning a electric motor past a magnet. I got a new one. I should get it in today/tonite.
 

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Discussion Starter · #6 ·
New water pump, no change. I can hear it at idle and reving. So I pulled the belt and started the truck. No noise! So it must be something the belt turns. I checked the idler on the tensioner and I believe it is good. I thought it was an old one, but it was only the spring part that was old. I have one other idler and it is new, but when I grab it, I can tilt it a bit. It turns nice, but doesn’t seem right, so I guess that’s my next thing to change. If it’s not that, it has to be the alternator or AC. The alternator is old, but it spins so nice. The AC compressor is also new. (2000 miles ago)
 

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New water pump, no change. I can hear it at idle and reving. So I pulled the belt and started the truck. No noise! So it must be something the belt turns. I checked the idler on the tensioner and I believe it is good. I thought it was an old one, but it was only the spring part that was old. I have one other idler and it is new, but when I grab it, I can tilt it a bit. It turns nice, but doesn’t seem right, so I guess that’s my next thing to change. If it’s not that, it has to be the alternator or AC. The alternator is old, but it spins so nice. The AC compressor is also new. (2000 miles ago)
I have had the rear bearing in the alternator fail early on mine a couple of times over the years...
 

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Stethoscope while it was running placed on the rear of alternator, seems that it only had symptoms with the belt tension on it.
 
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This is a bit of a long shot but there could be a bad bearing in the fan hub assembly. Those bearings are very good but do go bad and need replacing from time to time.
 

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Discussion Starter · #14 ·
So went down and bought a stethoscope and a new idler pulley. Bolted the idler on and the sound is gone. The old idler still looks new, just a bit too much play in the bearing. Probably could have just replaced the bearing. Anyways, the stethoscope can wait for another job.
 

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Discussion Starter · #16 ·
Well shucks. You mean you won't have to tear the hole engine apart to find the noise. LOL. I got close when I mentioned the bearing in the fan hub.
Yea, actually this idler takes the place of the fan hub. (I have E-fans) So you were pretty much bang on. So I guess I didn’t need the water pump. (It was pretty grundgy anyways)
 

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Discussion Starter · #18 ·
So I spoke too soon. It seemed fine at idle, but on my first drive, the sound is still there. It is definitely gone if the boost is over 15 psi. So that tells me it’s not a leak. (I hope) I tried the stethoscope and I can’t tell anything at idle.

It would appear it must be the alternator or the AC compressor. I kind of hate to replace either of these just to see. There’s no difference in sound when I turn the AC off or on, but since the main bearing turns all the time, that doesn’t really rule it out.

Im keen to make absolutely sure its belt driven. Do you think I would do any damage to drive it a few hundred feet without a belt. (No waterpump)
 

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You probably won't do any damage so long as there is water in the engine. It would take the water a while to get to 180 deg on a cold start and you still get a certain amount of cooling from the radiator even though your water pump isn't functioning. An old farm tractor we had didn't have a water pump. If you take the belt off and the noise goes away then you have narrowed it down to that part of the engine.
 

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Discussion Starter · #20 ·
So I drove the truck without the belt. There is no noise. Since I have a new water pump and idler, it must be one of three things. Alternator, AC compressor or the idler on the tensioner. All three turn nice as can be by hand.

The tensioner itself is old, but I had to switch the idler on it because I needed one without grooves. I think it is brand new, but I’m not sure because I have a lot of parts, new and used in a box. (It looks new)

The AC compressor is new 5 years ago, but it has just been sitting in a box during that time.

The Alternator is used. I spun it with a drill just now and it turns nice. (I don’t know if the drill turns as fast as the motor.)

Im really at a loss. I’m thinking of ordering a new alternator.
 
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