2005 Toyota Sienna Noise from belts

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I have a question regarding a noise coming from my wife's 2005 Toyota Sienna. Specifically, the noise comes from the area (when you open the hood and look in) on the left where there are several belts spinning. This noise is the absolute worst when it gets wet or excessively humid, but is very temporarily silenced when I spray WD-40 on the gears and belts area. I've read on several websites that it's the belts (specifically that they aren't tight enough or the bolts that hold the gears&belts into place aren't tight enough). However, I tugged on the belts in this area and they are all very tight and as far as I could tell, the bolts are all tightened as well. Now, I'm taking my car in to get an oil change here in the next month or so, but I wanted to ask what you think the noise might be? I'm fairly certain I can't fix it on my own (if you think I can, that's great), but I'd like to have some idea of what I'm facing when I walk into Firestone this/next month and have them look at it. I took it into the dealership I bought it from (used) shortly after I bought it and they fixed a few things for free (mostly some panel lights and such), including this noise, but I'm betting they just sprayed a ton of WD-40 on the gears and gave it back to me. Any advice you could give would be much appreciated!

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Monday, February 10th, 2014 AT 12:03 PM

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I can guarantee they did not spray anything on the belts. No professional would do that to a customer's car. A belt squeal is caused by a loose belt sliding over a pulley with lots of drag, like the power steering pump or generator, or more commonly by sliding across a pulley as it goes around it. That is caused by a pulley being tipped or turned.

Serpentine belts must never have any kind of dressing or lubricants applied to them. Water will make the squeal change just as effectively as WD-40, but it will not make dust and road dirt stick to the belt. That impacted dust will make even a good belt squeal. It will take from minutes to days for that to show up again, but it will.

The first step is to sight down along all of the pulleys and try to find one where the belt is peeking out to the side relative to all the other pulleys. 1/16" off-center is more than enough to cause a horrendous squeal. If you can see where it is not centered, either that pulley or the one right before it is tipped. Most commonly the bearings in idler pulleys develop looseness from wear. Spring-loaded tensioner pulleys do that too, but it's usually because the aluminum arm corrodes and wears away around its pivot bolt.

Once the offending pulley is replaced, the belt must be replaced. Before installing the new one, the pulleys must be washed with soap and water or engine degreaser. Be sure to tell your mechanic that the belt is contaminated, otherwise he will assume it is not, and may be inclined to not replace it to save you some money. The only other time they recommend replacement is if the belt is dry-rotted. The rule of thumb is when you look at the ribbed side of the belt, there should not be more than one crack per inch. It's normal to find a lot of cracks but if they're further apart than that, there is no urgent need to replace it.

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Monday, February 10th, 2014 AT 1:48 PM

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