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A service advisor at a vehicle repair shop recommended belt conditioner to help ensure longevity of rubber belts (timing, serpentine, etc.) and as a possible inexpensive fix to various engine noises.

Belt conditioner comes in a spray bottle, and you simply spray it onto the exposed surface of any rubber belt.

Although he highly recommended the product (and it is much less expensive than any repairs), I am concerned that such a conditioner would be counter-productive. It seems like a belt conditioner could attract dust and debris, as well as form a gummy residue on pulleys.

Are belt conditioners safe to use?

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    Nice question! Curious to see what folks here have to say. – Lynn Crumbling Sep 29 '16 at 11:56
  • Every time I've used belt conditioner, it has flipped my 'belt squeal' condition like an analog switch. Once, on a road trip I was surprised by a deep puddle at 45+ mph. The engine seemed fine but had developed a nasty belt squeal. I bought some conditioner, gave it a quick spritz, and presto-no-squealo. Several other times, tooling around under the hood while listening to the car radio, I thought I'd give the belt a spray to prevent squeal due to excess alternator draw on startup. The belt would squeal for the first 15 minutes of my shakedown drive. Does belt conditioner work? I have no idea. – MooseLucifer Sep 29 '16 at 12:59
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    I would take issue with the comment that belt conditioner is "much" less expensive than the repair. A replacement alternator belt is usually less than the price of a posh coffee and fancy sandwich and witting is seldom more than a ten minute job with only basic tools. – Steve Matthews Sep 29 '16 at 13:13
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According to manufacturer Dayco (Why Belt Dressing Is Not a Solution To Quiet a Noisy Belt), it should not be used.

In the past, simply covering a noisy serpentine belt in belt dressing would quiet that pesky belt. That’s when belts were made of neoprene. Today, you should never put belt dressing on an EPDM-made serpentine belt. Belt dressing, and other oils and solvents, may quieten the belt noise when first applied, but these oils will actually cause the belt’s rib surface to become more aggressive once they dry out, leading to even more belt noise issues.

The article goes on to explain how it can actually make things worse.

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As a fix for a squealing belt... no, I don't like it. Find the root cause and fix it. As a tool for increasing belt longevity... they last a long time on their own, I don't think I'd extend the normal maintenance interval on belts because I sprayed that stuff on them. So, it seems like a waste.

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Belt conditioning products are effectively Armor All spray for your belts. There may be some validity to claims that a belt conditioning product can extend the life of a belt by preventing the compound from drying out and breaking down. This is conceptually similar to how Armor All or comparable products help prevent old tires from cracking.

That being said, a belt cracking and breaking is not the only issue to be avoided. An old belt can stretch and wear down (just like tire tread) such that it is no longer holding your pulleys tight (even with an automatic tensioner). Moreover, you are spraying lubricating liquids on parts that function through friction, meaning you could cause a belt to slip on the pulleys which would effectively be the same as a belt snapping and not pulling the pulleys at all.

Spend the $7 (plus labor) to replace your belt. It is a relatively inexpensive component of regular maintenance and can prevent substantial engine damage in the future.

  • Belt conditioner is not a lubricant, it's actually pretty sticky. – MooseLucifer Sep 29 '16 at 17:50
  • Just because something is sticky does not mean it is not a lubricant. Take for instance Red-N-Tacky, which is a lubricant grease specifically designed to be sticky. It lubricates gears well, but also helps hold tiny bearing rods in place, such as when reassembling a transmission or transfer case. – Tyler Sep 29 '16 at 18:34
  • There may be some conditioners that containing lubricating agents such that when a belt does slip, it does not also squeal, but in my experience, most conditioners contain tacking agents to prevent that slip altogether. The Red-N-Tacky seems to be designed to suspend things together in a matrix, whereas belt conditioner aims to adhere two surfaces to each other through direct contact. – MooseLucifer Sep 29 '16 at 18:59

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