A serpentine belt usually drives the alternator, water pump, power steering pump and air conditioning compressor, so when it snaps they all stop at once. Squealing, chirping, cracks or glazing on the ribs are the warning signs, and the tensioner should be checked when the belt is replaced.
A single belt usually drives the alternator, the water pump, the power steering pump and the air conditioning compressor. That efficiency is also the problem: when the belt fails, everything it drives stops at the same moment.
What happens when it snaps
The battery light comes on because the alternator has stopped charging. The steering becomes very heavy because the pump has stopped. And on most engines the water pump stops, so the engine begins overheating within minutes. You have a short window to get off the road safely, and continuing is how a belt becomes a head gasket.
The warning signs
A squeal on start-up or when you turn the wheel at low speed, which is the belt slipping. Visible cracks across the ribbed side, which is normal wear until there are several close together. Glazing, where the belt surface has gone shiny and hard. Missing chunks from a rib. And a chirping noise that changes with engine speed, which often points at a pulley or tensioner rather than the belt itself.
Check the tensioner too
A belt is held at the correct tension by a spring-loaded tensioner, and a tired tensioner will let a brand new belt slip and squeal. Replacing the belt without checking the tensioner and idler pulleys is the most common reason the noise comes straight back.
Why city cars go through them
Constant stop-start running, heavy air conditioning use in summer and frequent steering at low speed all load the belt more than steady highway driving does.
What to do about a squeal
Have it looked at rather than ignoring it. Belt dressing sprays quieten a slipping belt temporarily and do nothing about the cause. See engine diagnostics and engine repair.
Midtown Center Auto Repair, Long Island City. Contact us.
Serpentine Belt: Questions
What happens if the serpentine belt snaps while driving?
When the serpentine belt snaps, the battery light comes on, steering gets heavy on hydraulic systems, and the engine can overheat quickly because the water pump stops. Pull over safely.
How often should the belt be replaced?
Follow the interval in your owner's manual, and replace it sooner if it shows cracks, glazing or fraying.
Is a squeal always the belt?
Usually the belt or its tensioner, but a failing pulley bearing can also squeal. A quick inspection tells which.
