Please disregard my post about cleaning the sullies - I was thinking V belts - DOH!

I asked my dealer how they evaluated accessory belts for wear - they do not evaluate them, they just change them on their maintenance schedule.

The new EPDM belts DO NOT crack, they just wear out like tire treads do.

Gates Belts make a gauge to check the grooves for wear. I got a couple for free from Gates (I put my son-in-laws name on a second request so he could get one.

I go to a small general repair garage to get my State Vehicle inspections and they have a Gates Belts display that explains how the gauges work.

Gates tells usl that worn accessory belts slip long before they squeal.

If the squeal went away when you put the crap on the belt.

I suggest that you remove the belt, clean the pullies with a mild solvent such as alcohol, then install a new belt, properly adjusted. Keep the old belt as an emergency spare.

Crap? Yes, WD40 was designed to repel water when moisture could cause issues with old ignition systems and other electrical systems. The original stuff was not a lubricant although its modern version has lubricant. If you want to see if your WD40 has lubricant in it, spray some on a window and check it for residue after it dries.

If this is the original accessory belt, get a new belt/idler pulley.

Never, never spray lubricant on a belt, it causes the belt to slip! The squealing noise should have been and now must be investigated. Where is the noise coming from? Belts normally do not make any noise, but non turning parts do!!
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Keeping it running is better than buying new

WD40 is an overpriced solvent ideal for cleaning oil paint or roofing tar from
your hands, clothes and stuff, not for lubing belts or pulley sheaves.

Clean the belts and pulleys and recheck belt tensions.
Insure that there are no pulley alignment issues.

Cheers, Bill