Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Fan belt squeal

my fan belt squeals sometimes when I start it up. What causes this. It is a 1995 Mazda Miata

When rubber is cold it it gets larger. When it heats up it shrinks.

When you first start the engine the rubber belt is cold. So it’s a little bigger. When you start the cold engine, it draws a lot of energy from the battery to turn the starter over. Once the engine starts, the alternator comes immediately on line to replenish the energy in the battery that was used to operate the starter. This causes a heavy load on the alternator where it makes the alternator harder to turn. The belt then slips on alternator pulley causing the squealing sound until the belt heats up from friction and then shrinks or gets smaller. The belt then stops slipping on the alternator pulley and the squealing stops.

A worn belt and/or a worn belt tensioner can cause this.


A belts sole job is to transfer the power / torque from the crank pulley to all the accessories and it does so through the wedging force of the belt and correct belt tension placed on it by the tensioner. Belt squeal or noise usually indicates loss of tension in the accessory belt drive system. This loss of tension can come from a couples of different areas and I would begin with the tensioner if it has one, replace it if the vehicular has any age. Secondly material loss in a belt can cause a similar problem. If the belt is squealing it is creating heat and losing material which means it is no longer griping the pulley. A belt is made similar to a tire (you replace those don?t you from wear?) and just 5% loss of belt material will create a loss of tension /grip as well. As mentioned high amperage alternators place a tremendous load on the system. A slipping belt from loss of tension will also facilitate pulley wear. Once that happens, though difficult to detect, you must also replace the pulley as well.

To end I will say that a slipping belt is the worst thing that can happen to today?s belt system. If it continues, it creates a tremendous amount of heat as it slips that travel into the bearings. It can also create false engine codes and the accessories such as the alternator or A/C may be operating at a diminished output.


? Remove belt, inspect and clean all pulleys with soap and water or alcohol based brake cleaner
? Replace belt and tensioner together

Hope this helps


Abour a year ago, my van started making jingling noises under the hood. I replaced the tensioner and idler pully and then the A/C clutch but it still made noise. Then the belt started squeeling and if I run water on it it stopped. So I replaced the belt and it has been fine for several months. MY granddaughter’s husband drives a Ranger and the belt has been squeeling for a year or so. He just keeps driving it.