View Full Version : How tight should a serpentine belt be?

Dream of the iris
03-02-2011, 09:14 PM
I recently got my car looked at and the mechanic said that it looks like the serpentine belt is beginning to fray.

This is strange because I got it changed in October and have not put nearly enough miles on it to warrant a change so soon.

When it was recently changed, it was beginning to make noise when I turned on the AC- so I took it to the mechanic who changed it and he tightened it for me.

This new mechanic suggested that the belt was "too tight" as grooves are clearly visible, sticking up from underneath the belt.

So, I told the mechanic who changed the belt the first time about the problem and he suggested that a serpentine belt cannot be too tight or that shouldn't cause any problems.

Is he right? Can a serpentine belt not be too tight?

03-02-2011, 09:20 PM
They tend to have a recommended tightness which is usually measured by deflection. It's also common for a belt to have a tensioner, though.

If a belt were to be really fucking tight, it could conceivably cause unwanted friction and heat which could lead to the material of the belt degrading. But I've no personal experience of this.

Charles Manson
03-02-2011, 09:35 PM


03-02-2011, 11:06 PM
I recommend putting on a belt the same length as the one the car originally came with. As long as the tensioner isn't shot it will handle the rest.

Oh, and get a new mechanic asap.

Dream of the iris
03-03-2011, 01:35 AM
You saying he's wrong about it then?

03-03-2011, 01:40 AM
Dude... how did he tighten the serpentine belt?

I mean, you can't shorten the belt... and it's not like you can move the tensioner or idler pulley.

If it's bad, go pay 10-20 for a belt and put that sob on yourself.

a giant pterodactyl
03-03-2011, 03:05 AM
OP, most likely you have a mechanical or hydraulic belt tensioner.

a tensioner keeps constant and correct pressure on your belt. your belt is most likely CRACKING not fraying.
i am a professional mechanic and my advice is to change your serpentine belt and if it continues to squeal get a new belt tensioner.

if this is an older car you may have a V-belt. that type of belt is tightened to a certain pressure and does not have a tensioner to keep constant pressure on it.
v-belts need to be tightened periodically to maintain proper tension.

if you could possibly give the year and make of your car i can help you better.

belts are usually simple enough that you could do it yourself.

Dream of the iris
03-03-2011, 05:51 AM
03 toyota echo.

The belt does not squeal, btw.

03-03-2011, 10:40 AM
Is it a spring loaded/hydraulic tensioner that automatically tensions the belt, or do you have to manually tension it by physically moving a part that's driven by the belt and tightening the part down? Because if it's the former, automatic tensioners will pretty much never over-tighten the belt - but if you try really hard, you can over-tension a belt that's manually tensioned.

a giant pterodactyl
03-03-2011, 04:03 PM
lol, i worked my ass off on this.

here is the complete procedure for belt replacement/tensioning for your car.


i put it in .pdf format and put it on SCRIBED so you could print/download etc.

looks like your car has to have belt tensioned by moving the alternator.

if you are even remotely mechanically inclined you can do this yourself. dont get ripped off by your 'mechanic'