Okay, any ideas are appreciated because it is driving me crazy.

2002 W208 M113, all service records since new, so well taken care of.

It began what sounded like a serpentine belt squeak when cold last summer. Since it is only driven in the summer, I kind of forgot about it until this summer. It only happens when the engine is cold, once warmed, no squeak. Mostly everything on the FRONT of the engine is brand NEW Mercedes parts.

Serpentine belt
Idler Pulley
Belt tensioner
Water pump
AC Compressor
Alternator
Viscous fan clutch
(also new motor mounts)

After all of these new parts... squeak is still there. The crank pulley looks straight and while the belt was off, I spun the power steering pump pulley (sounded fine), and "respun" all of the pulleys by hand. Once the belt was back on, and car running, I tried to locate the squeak with my stethoscope. NO LUCK. Interestingly... the sound seems to be coming from the passenger side of the engine somewhere.. If I start it with the serpentine belt off.. it seems like the noise is GONE.

Any ideas????

Thanks so much.

My guess is the water pump. They make a squeaking sound sometimes, especially cold. Its not indicating failure of the bearing but instead is just a noise from the carbon / ceramic seal that keeps the water inside the pump.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Thanks for the response. The water pump is brand new as well. Interestingly, when I replaced it, it wasn't really making any terrible noises, but the impeller was actually slightly binding on the body at one point in the revolution.

The squeak is exactly the same with the new pump on there as it was with the old one.

On the chance that it is, in fact, the pump seal, try a can of soluble oil (aka, "Water Pump Lubricant") in the cooling system.

Inspect the fan bearing bracket for signs of wear, like metal shavings. By the way, how many miles are on this vehicle?

__________________
Fred Hoelzle

No metal shavings. Anywhere. The car has 90k miles, but has been "stealership" maintained since new. It is in excellent condition and everything has been replaced as needed. No deferred maintenance.

Went and listened closely. It definitely sounds like it is coming from the passenger side of the engine near the front. Once the temperature has increased... gone.

An M113 does not have a fan bearing bracket.

While the engine is running and making noise, mist some water on the flat side of the belt. If the noise goes away, the belt is making noise.

When it is making noise, is it a slow chirp, pause, chirp or a constant chirp, chirp? Have a look for the label on the back of the belt and get a sense if the chirp is in time with the label passing across the flat pulleys.

To solve, sand the flat pulleys with some 80 grit to roughen them up a bit.

If the belt label is slick, sand that a bit too. I've had slick labels on new belts give a chirp , pause , chirp. If the belt is old but good condition, sanding the back of the belt a bit helps too.

And now for why you are doing all of this. Micro V belts generally tension and snake around the accessories by using flat pulleys on the back of the belt. These pulleys glaze over / back of belt becomes polished after a while. As the belt is used, it walks back and forth on the flat pulleys a bit causing the rubber to chirp / squeak. By sanding the pulleys they then grip the belt and no more chirp.

Vince, sorry about that. Being familiar with the inline-6 engines I presumed that all engines had a fan bearing bracket. It's a good thing not having a fan bearing bracket because it's a lot of work to replace one.

__________________
Fred Hoelzle

97 SL320 - Thanks for the thoughts. I'm beginning to believe it is the water pump pulley.. I will post my findings when I take it off and scuff it up or replace it....

Ugh. Water pump pulley replaced, another belt tried, the noise still remains.
Remove belt... noise seems to be gone.
Just to reiterate:

(All Mercedes brand parts)

New:

Alternator
AC Compressor
Belt Tensioner
Idler Pulley
Viscous Fan Clutch
Water Pump
Water Pump Pulley
Serpentine Belt

The only thing that hasn't been replaced is the crank pulley, but it makes no noise and is not wobbling with the belt off. Interestingly, if I turn the headlights on, therefor putting a heavier load on the alternator, the noise seems more consistent. Again, it made the same noise with the old alternator as well.

Hair pulling coming in 5,4,3,2......

Did you do everything on my post 9? What were the results?

97 SL320.. Interestingly the water seems to make a difference sometimes, but because of the intermittent nature of the noise, it is hard to tell if it actually doing anything. I actually replaced the only smooth pulleys, the water pump pulley and tensioner...

I've already told you what's going on. A low pitched squeak cold is the water pump seal. Its not bad its just what about 1/3 of them do. If you just ignore it long enough the seal will probably wear to the point it stops making noise.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff