Car has 31000 miles, no fluid leaks, serpentine belt looks and feels tight. No voltage problems. No abnormal codes on computer! Performs fine, noise will only repeat next cold start.

Any similar experience or thoughts from the readers out there?

thanks in advance for your reading and response.

 

I would begin with removing the belt and checking all the pulleys. Visually check the belt action first while it is running, look for any wobble going on. See that the belt is seated in each pulley perfectly. Be careful to not get your hands hair or necktie caught in the damn thing. LoL It actually can be dangerous. If you have safety glasses, wear those. Then remove belt and check all the pulleys including alternator and water pump. 31K is low miles for any of the pulleys to be worn but it's possible and this is one of the symptoms. Maybe all the pulleys are okay and the tensioner has begun losing its strength. Have someone start the car while you are up front listening to see if that's the location where the noise is coming from. Don't go on long trips until you do get the issue fixed, whatever it is. Hopefully if you don't work on the car yourself, you have an independent shop you can trust and don't have to take the car to a MBZ dealer, some of them are robbers with no conscience. If it happens that you are driving and the belt goes south, shut the engine off IMMEDIATELY and don't try to drive home. Hope you have towing cost covered with your insurance or AAA. If it so happens that you do wind up needing a tow, be advised that while AAA used to tow a car "home", nowadays they will "only tow a car to a repair shop". All five of my cars have new belts and all new pulleys! And I'm glad, those pulleys wear out. The one that made a noise for a few starts and then threw its belt off, shredding it was my Maserati. It only made noise at startup about three times then about ten blocks away from the house suddenly the car ate its belt. If it is a pulley that's making your noise it is definitely about to sieze. Luckily on the Maserati was only a worn out pulley, and all new pulleys, tensioner and new belt on that thing cost $1050. Most average Mercedes could be cheaper although the SL63 has got some pulleys that are quite expensive. My SL55 AMG has a dual idler pulley that costs over $700 from Mercedes, and the harmonic balancer is also a dual belt pulley that has a molded rubber piece inside it that deforms with heat and age, and begins to wobble, that part costs over $700 also. For the "simpler" Benzos like the ones with an M273 V8, a new belt & pulleys kit from Continental costs under $200., and a kit for R170 SLK cost closer to only $100. My SL55 didn't make any noise but the alternator failed because a previous owner had installed a cheap junk part which failed one day as I was driving, and upon removing the belt my mechanics found the water pump was just about ready to explode, and the dual idler pulley was worn out as well, and once back together with new parts the belt still didn't track right because the crank pulley/harmonic balancer was also deformed. After some $$$$, it's all perfect again with all new parts. Never use cheap junk parts on these cars!! A Bosch water pump, Bosch alternator, just what the car was born with, those both cost around $300 or so if I recall. Duralast alternator? Under $100. LOL but not worth ten cents

 

Squirt water with spray bottle on hose when you hear noise, if noise goes away then bad belt. If you change belt change at least the plastic idler pulley(s) and tensioner. I have cheaped out on this in the past and always regretted it.

 

Sort of impossible to squirt water on the pulleys if the sound goes away after ten or 15 seconds. You could spray water on it and the sound was already gonna stop so the water tells you nothing? You can try it, it's your car. Any time the belt is off every pulley needs to be checked for smooth turning, looseness, gritty turning, wobble, and correct resistance to turning, Any question at all replace!! With 31K miles it's possible that just your belt has stretched, but since it is a Mercedes..... LoL Murphy's Law comes into play. It is an SL63 so with supercharger those pulleys don't have a very easy life. I believe the SL63 has two belts... The biggest pulley, the harmonic balancer can be hard to tell visually if it's got an issue, but if all else is certifiably correct and the belt still seems to track a bit funny visually, which is what mine did, then that can likely be the cause. I am with belts the same way I am with spark plugs: If it comes outta the car it's not going back in. Some people will remove spark plugs to inspect and then put back in. This seems insane to me! Those may cost twelve bucks or more, but if they're taken out they get replaced with nice fresh ones. Same with the belt. It might look fine but can be stretched. A new belt might be all you need, but definitely check everything you can while the belt is off. My engineer mechanic friends live by this rule, whenever the car is being worked on to the point that you have now got access to check anything that you couldn't otherwise, check everything! And if changing that harmonic balancer always replace at the same time, the front main seal since it is right there and only costs about $35.. since, with the harmonic balancer off, you have access. New is always better that seemingly perfect old. Let us know what you find out! Kind Regards

 

Sounds like an Idler pulley issue to me, I replaced all of the Idler pulleys on my 55 with UPD due to having some friends who have had their stock pulleys crack.

 

Thanks, nothing on computer eval, pullets and belt/tensioner check ok, only thing I found, the power steering fluid volume was slightly low, topped it off and the start up noise disappeared! will sit on it until it recurs, thanks for the response! will update as it evolves.





Love this car!

 

Have someone else start the car while you are monitoring under the hood.