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Old 07-24-2013, 05:51 PM   #1
saturn
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Serpentine belt melting on Tension & Idle Pulley

Hi Guys, this is yet one of those mysteries where I say experience counts. I am still in learning stages of my E60 and have done few DIYs lately and thanks to all the good people here most of them were successful. But this one has stumbled me and I am hoping it is minor but could leave me stranded in the worst case scenario.

I recently changed my engine tension pulley, Idler pulley, AC Tension pulley, Serpentine belt and AC belt with OEM brands (NAPA, Contitech -main , Optibelt - AC). All was well until my water pump and thermostat gave up last week and was leaking coolant. While I was fixing the water pump and tried to take off the serpentine belt, it was nearly stuck to the tensioner pulley. After removing the belt, what I found was that both the tensioner pulley and the idler pulley had worn off/melted rubber on the outer edge. This is where the belt was sticking on to. I inspected the belt, but it is not showing any major signs of damage. I have attached a picture of the tensioner and idler pulley where you can see the rubber on the edge.

The hot coolant was leaking from thermostat and the water pump and getting sprayed (very fine drops) to the right side of the vehicle at the same level as these pulley, but I doubt that would have caused any rubber to melt. Questions I am wondering to myself;
Is this normal?
Is something going wrong?
Hope I won't loose the belt in the middle of a highway or something....

All suggestions are welcome.
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Old 07-24-2013, 06:35 PM   #2
Zell
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It looks to me like it has worn grooves into the pulleys from just the pulleys being old. Mine were originally like that as well: fairly obvious grooves in changeable pulleys.
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Old 07-24-2013, 07:15 PM   #3
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Check your pulleys and make sure they move freely.

Did you.have the belt on correctly?
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Old 07-24-2013, 07:48 PM   #4
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Quote:
Originally Posted by BMWCaptain View Post
Check your pulleys and make sure they move freely.

Did you.have the belt on correctly?
Both those pulleys and the belt are new (none of them are old, that is the reason of concern) and changed at the same time. The belt is on correctly and only the flat side of the ribbed belt touches these two pulleys, all other wheels (4 - water pump, alternator, power steering, engine) have the ribbed side of the belt.

Both Tensioner and Idler pulley move freely.

Last edited by saturn; 07-24-2013 at 07:49 PM.
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Old 07-24-2013, 07:57 PM   #5
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Heat. You're building up friction somewhere. Take the belt off and make sure all pulleys (alternator, etc.) turn freely. It could be the tensioner. If it's not keeping the belt tight, it could be slipping, which could cause friction. Watch the belt with the engine running. Have someone rev the engine to about 3,000 rpm or more, and see if the belt stays tight. The only other thing I can think of is to use a strobe light and tune it to the belt rpm so you can "freeze" it and see if it's "flopping".
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Old 07-24-2013, 08:02 PM   #6
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Coolant is very slippery, it's possible that it made the belt slip, overheated it a bit and caused it to stick to the plastic. If all the pulleys are spinning fine and the belt is on the right way, I wouldn't worry about it.
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Old 07-24-2013, 08:07 PM   #7
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If it's melting, that means heat buildup on a non load pulley. Meaning, that these pulleys would not slip anyway. The only pulleys that would slip are the loaded pulleys. That is the Crank, water pump, alternator, AC compressor, and power steering pump.

OP this is a shot in the dark, but does your belt have the correct number of grooves?
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Old 07-24-2013, 09:22 PM   #8
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It could be related. What exactly gave up on the water pump??? If it was bearing related, the extra head from the bearings could have transferred to the pulley on the water pump and the excess heat caused your belt to degrade and become soft, then it transferred to the plastic pulleys. Clean then, then run it.
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Old 07-24-2013, 11:17 PM   #9
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Quote:
Originally Posted by WDE46 View Post
OP this is a shot in the dark, but does your belt have the correct number of grooves?
Thanks WDE46, the belt was OEM Contitech 8pk 1538. No issue with the grooves.

Quote:
Originally Posted by BobbyC View Post
It could be related. What exactly gave up on the water pump??? If it was bearing related, the extra head from the bearings could have transferred to the pulley on the water pump and the excess heat caused your belt to degrade and become soft, then it transferred to the plastic pulleys. Clean then, then run it.
Not sure what happened with the pump, but it was leaking along with the thermostat. I cannot tell if the bearing was totally gone or not but it seemed to be fine. Pump is replaced, pulley has been cleaned. I guess, I will just wait for a week and pull out the belt again to see what happens in a weeks time.
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