Engine belt or pulleys

Serpentine belts must never have any type of lubricant applied to them. Squealing is usually caused by the belt sliding across a pulley as it goes around it, and lubricants make that easier to occur.

Three things can cause the belt to squeal. The least common is when there is excessive wear on the ribbed side, those ribs may not sit deep enough into the grooves on the pulley to grab it solidly. Serpentine belts are considered ready to be replaced when there's more than one crack across the ribbed side per inch. That almost always occurs before the ribs become worn enough to cause a squeal.

The second cause is a weak spring-loaded tensioner pulley, or one that is rusted tight. I suspect this happens more often to cars that frequently sit for long periods without being driven. This would probably be a less likely cause after driving for six hours.

The most common cause of belt squeal is when one of the pulleys is turned or tipped due to a worn bearing. Most smooth pulleys are painted black, then that paint wears off where the belt runs in that area. Look for a pulley where the edge of the belt is running off to one side a little, and on the other side you can see shiny silver metal showing. Also, sight down from one of the highest pulleys to one of the lowest, then look at those in the middle to see if the side of the belt is peeking out and is visible. This can be rather difficult to judge, but if the belt is off-center by as little as 1/16", that is evidence it is sliding across that pulley or the one right before it, as it goes around it. You can verify this problem by lightly dribbling a little water on the smooth backside of the belt while the engine is running and the squeal is occurring. If the noise changes, suspect a tipped or turned pulley. Those will rarely be a ribbed pulley as those are on things that rarely develop worn bearings. That includes the generator, power steering pump, AC compressor, and crankshaft pulley. Ford has more problems with idler pulleys and tensioner pulleys causing the squeal.

In my sad drawing, the right part is showing looking down from on top of the engine, then on one of the mid-level pulleys, the red area is where the belt is off-center and is peeking out on the side. Remember, 1/16" off-center is more than enough to cause a loud squeal, and this can be rather hard to tell.

A fourth cause is real uncommon, but worth mentioning. If you drive on dirt roads or in dusty conditions, small rock particles can become embedded in the smooth side of the belt. This tends to cause more of a pinging sound that you might not even hear from inside the car. If this is really bad, you can reduce the noise with a flat file. You have to be real careful when doing this to avoid the belt catching the end of the file and flinging it out. With the engine idling, hold the flat, blunt end of the file on the belt, at an angle pointing in the direction the belt is running. Put a little pressure on it, then watch for orange sparks jumping from the end. If you see those, it is caused by rocks hitting the file. If you move the file left and right across the belt, it will knock those rock chips off, then the sparks will stop occurring. Cleaning the belt this way works best if you hold the end where the belt goes around a pulley. The wrong way to hold it is in the way it would gouge into the belt if it caught it. The right way is if you held a finger on the file, it would be pointing in the direction the belt is running.

These rock chips are going to become a problem if you leave the belt with WD-40 on the engine. Dirt is going to stick to that and make the problem a lot worse. Once any other causes are found and solved, you'll need to remove the old belt, scrub all of the pulleys with soap and water, or engine degreaser, then install a new belt. You might want to save the old belt for a spare, but only use it as a last resort.