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Old 15 year old original belt.
Recently my Bosch air pump was making a electric saw noise sometimes, diagnosed by retired MB mechanic as air pump. Since I have not changed the serpentine belt for 15 year , I asked mechanic to change the top pulley(INA) and the belt ( GATES K060942 which is supposedly the same length of 2392mm) when he was changing out the air pumpand in the vicinity already, thinking that would be good preventative therapy for an old belt. All went well for 1.5 month because the weather was still warm.
Then the cold came and my 12 year old battery died. After installing a new AGM battery on my driveway to replace the 12 year old AGM battery,Mechanic tested the car, this time in much colder weather than when belt was first installed. Belt made chirping sound as if there were 10 or more birds chirping. Mechanic sprayed a few dropsof WD40 on the belt and the squeal went away immediately.But only for a few days. Now it chirps when car is cold or around freezing.
I told mechanic about the problem, he informed me (1) counterintuitive to install back the old belt which seems fine still(2) a new Mercedes belt may give rise to the same symptoms(3) a few drops of WD40 made the squeal went away, means problem only with the belt not the tensioner nor the alternator(4)lives with the problem, The squeal went away after 15 min of driving when car warms up. When engine warm, queal is not audible. Should I ask him to install back the old belt which did not squeal at all?
Are there any experience with belt like this, parts store does not sell exact MB or nonMB belt of 2392mm. FCGroton only sells 2397mm, not 2392! Thanks for any suggestion
Last edited by petaling; Nov 23, 2025 at 01:45 PM.
Reason: text
My Operators Manual says to use a 2401mm belt. I could not easily find that specific size so bought a Continental 6 PK 2404 and it fits great. Think I paid around $15 for it. Oddly enough a 2390mm belt was previously installed.
My Operators Manual lists the C250 belt as 2401mm.
MB does have a solution to a squeaky belt by applying a product to the sides of the belt, not on the flats.
On the tensioner there are markings indicating how tight/loose the belt is fitting. Where does this show on yours?
Thanks,
My owners manual also says 2401mm poly belt for a v6 2.5 litre engine 204.085. However, the new car came with the 2392mm MB belt 15 years ago ie the original belt
The WD40 was just to show the noise disappeared with a few drops. Something to do with the belt only not anything else?
I"ll try to find a source for the Krytox lubricant. My mechanic told me he used to use a wax stick before but he has run out of it since he's retired ? Does it sound like a similar idea?
The krytox stuff is one of those very expensive products that comes in a small amount. Similar category to the MB sunroof grease they recommend. I believe the Krytox 0009893660 is Krytox GPL 105 lubricant. Seems used to lubricate the edges of the belt where it contacts the edges of the pulleys. I wouldnt run out and buy anything until you investigate further to see if you can find the cause.
You say you have the belt and the idler pulley replaced and it ran fine, no squeal. But then your battery died and you installed a new battery, and right after installing the new battery the belt has been squealing every cold start?
The only things you can think of that has changed is new battery and the weather is colder?
Do you drive the car daily?
Before you start the car open the hood and inspect the belt, look for any signs of moisture on it. Then start the car and try and pin point where the squeal is coming from. Left side, right side, try to narrow it down.
When searching "Belt squeal" there are all different causes and resolutions.
The krytox stuff is one of those very expensive products that comes in a small amount. Similar category to the MB sunroof grease they recommend. I believe the Krytox 0009893660 is Krytox GPL 105 lubricant. Seems used to lubricate the edges of the belt where it contacts the edges of the pulleys. I wouldnt run out and buy anything until you investigate further to see if you can find the cause.
You say you have the belt and the idler pulley replaced and it ran fine, no squeal. But then your battery died and you installed a new battery, and right after installing the new battery the belt has been squealing every cold start?
The only things you can think of that has changed is new battery and the weather is colder?
Do you drive the car daily?
Before you start the car open the hood and inspect the belt, look for any signs of moisture on it. Then start the car and try and pin point where the squeal is coming from. Left side, right side, try to narrow it down.
When searching "Belt squeal" there are all different causes and resolutions.
I know one of the nz member took nine months because he used a 2400mm belt instead of of a 2300 belt. Finally solved after he replaced with a correct size belt.
https://mbworld.org/forums/c-class-w204/807335-drive-belt-noise-c300-w204.html
Last edited by petaling; Nov 24, 2025 at 02:32 AM.
My Operators Manual says to use a 2401mm belt. I could not easily find that specific size so bought a Continental 6 PK 2404 and it fits great. Think I paid around $15 for it. Oddly enough a 2390mm belt was previously installed.
My Operators Manual lists the C250 belt as 2401mm.
MB does have a solution to a squeaky belt by applying a product to the sides of the belt, not on the flats.
On the tensioner there are markings indicating how tight/loose the belt is fitting. Where does this show on yours? THANKS TIM,PICTURES BELOW
[img alt="Another of tensioner markings
"]https://cimg4.ibsrv.net/gimg/www.mbworld.org-vbulletin/2000x1504/img_7139_e63266907c33becbc7283f27cf84af4a910f04a7. jpeg[/img] Another of tensioner markings Took pics this am. Temperature in garage 6.5 C ,outside garage 6C=42.8 °F.No squeak this start. Tensioner marking normal? Thanks THANKS TIM,PICTURES ABOVE
Last edited by petaling; Nov 24, 2025 at 10:37 AM.
Ive used Both gates and continental and never had any result in squealing. Are you sure it is not from slight condensation in the mornings? One inexpensive product people dress their belts in is 303 protectant...but you should not have to dress a belt. Considering it has run for for a few months it should be worn in if it had any contact points which is why I would suggest condensation.
Update: changed back to old Mercedes belt. It feels thicker and more supple than the Mexican made Gates belt. The Gates was very firm almost hard.No more squeal now in cold with factory belt.. If I do need anew belt in the future I’ll get a Continental 6K2397 from Europe ,hopefully it’s the same quality as the Genuine Mercedes 6K2397 sold by FCPgroton.picture of old belt and tensioner mark
Last edited by petaling; Nov 28, 2025 at 02:57 PM.
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