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Discussion Starter #1 (Edited)
Hey all,
The noise comes from the engine compartment. With the hood open, I can locate the sound in the turbo and alternator area.
The sound normally sounds like a sound of a slipping belt. Very high pitch noise that seems to go up with RPM increase. At idle or below 1000 rpm there is no noise. The sound is loud so that it can be heard from 100 feets away.

Now it would be a simple thing if it actually was a slipping belt! But I suspect that is not the case, for the following reasons.

I owned the car for past 1 year. The sound is inconsistent, it comes sometimes and not others. So, far I have found only a couple of patterns.

1. The sound has some connection to the Heater. about 50 or 60% of the time, the sound will come on when the blower is turned on and will go away when blower is turned off. But as I said, this will not happen all the time, about half the time. This throws me completely off! Does the heater or blower has any clutch that is kicking in putting more tension on the belts? if indeed it is the belt. Or is does the alternator has any clutch depending on the load? if I am putting more load by turning on the heater?

2. The sound in most cases, when heater is not used, comes on at around 1200 rpm and will stay on through all the gears, and after 30 seconds or so it will go away at 2500 rpms or so. This is inconsistent too, as sometimes the sound will come on for 5 seconds and sometimes it will stay on for 5 minutes.


Possible scenarios could be, turbo bearing making noise? or air leaking in the turbo mechanism somewhere? or the most obvious the belts?

Also, I put on a new alternator and belts about 6 months ago. The same sound came before the change. The sound did go away for a few months after putting new alternator and belts, but than it came back.

Let me know what you think?
I will update as I recall more stuff.

Thanks,

Sam
 

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Hi

Sometimes a cheap stethoscope ($3 at Harbor Freight) can be very helpful in locating engine compartment noises.

Joseph
 

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Aux water pump? Did you check the tension on your belts?

Please update your CP/sig to include your car year and model.
 

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If you do not want to get a stethoscope you can use a piece of wood placed with care on the part you think the niose is comming from and your ear at the other end. I use a piece of old Broom handle.
I have a Stethoscope but I find it is too loud when I use it so do not use it often. Also the Broom stick is longer and I do not have to bend and get my Face as close to the Engine as is the case with a Stethoscope. And, yes I burned my Cheek on a hot Exhaust manifold ounce and now am more careful.
 

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Discussion Starter #5 (Edited)
Thanks for the reply guys.
Winmutt, it is an 84 300d. 260K miles.

Also, Winmutt, water pumps work or they leak, do they ever make noises?

from hearing the noise, everybody would say its a belt slipping! but with the for mention characteristics!

What I am surprised the most is the connection between heater/blower on/off and the noise I am talking about! I can not imagine any thing related to heat/blower have any relationship to the noise!

Like alternator putting more load and hence harder to turn? making the belts slip if a little loose? is that a possibility?

Do alternator have different load clutches or anything?

Thanks,

Sam
 

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Thanks for the reply guys.
Winmutt, it is an 84 300d. 260K miles.

Also, Winmutt, water pumps work or they leak, do they ever make noises?

from hearing the noise, everybody would say its a belt slipping! but with the for mention characteristics!

What I am surprised the most is the connection between heater/blower on/off and the noise I am talking about! I can not imagine any thing related to heat/blower have any relationship to the noise!

Like alternator putting more load and hence harder to turn? making the belts slip if a little loose? is that a possibility?

Do alternator have different load clutches or anything?

Thanks,

Sam
Hi

You may have answered your own question. Alternators do require more engine power when under load and this could lead to belt slippage with higher loads from lights, blowers & etc.

Joseph
 

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Discussion Starter #7
Thanks Joseph

Joseph,

So, are you saying that alternator's "rotating resistance" on the belts is higher, hence more torque required to turn it, under more load to the alternator? in my case sometimes from turning the heat/blower on?

I think that can explain a lot of it, if that is the case!

I always thought alternators always spin under the same rotational resistance and thus required the same/constant torque. (at any given RPM that is!)

Thanks,

Sam
 

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Joseph,

So, are you saying that alternator's "rotating resistance" on the belts is higher, hence more torque required to turn it, under more load to the alternator? in my case sometimes from turning the heat/blower on?

I think that can explain a lot of it, if that is the case!

I always thought alternators always spin under the same rotational resistance and thus required the same/constant torque. (at any given RPM that is!)

Thanks,

Sam
Hi

With many cars, you can have the engine at idle and when you turn on the lights you will hear the engine change tone - adjusting to the extra load.

It does appear you have a torque problem, the power isn't being transmitted from the crankshaft pully to the alternator pully correctly. It just shows up when you put more load on the alternator. Could be incorrect belt tension, worn belt or pully or a little oil or coolant getting on the belt. The belt should ride high in the pully groove and not touch the botton of the groove.

Good Luck

Joseph
 
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