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Mike, Mercedes Technician
Category: Mercedes
Satisfied Customers: 39198
Experience:  Tech Expert
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There I have a Mercedes C270, 2005 model. I am getting knocking

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Hi there I have a Mercedes C270, 2005 model. I am getting knocking sound from the engine
area which we are unable to identify the source. I have had 3 different opinions from 3 different sources. One says it is the engine -valve or bearing. the noise has not affected the performance of the vehicle and since it stated I have done substantial mileage. If it was a bearing etc surely the engine would have seized by now. The second opinion is that the knocking is coming from the gearbox area. The third opinion is that it is the compressor. The car seems to run well for a period of time and then the engine light comes
on and it goes in to limp mode. We then reset the settings and it seems ok again. I know this may be difficult without listening to the noise but do you have any thoughts?
Hello and Welcome -
My name is ***** ***** Im happy to help.
As you say, it is difficult to some degree anyway without hearing it...even WITH hearing it sometimes as you have found but the idea is to determine what sort of noise it, is it rotational..consistent with the speed of the engine..or a regular banging ..knocking and so on.
Sometimes you can narrow it down to the engine by putting the clutch in on a manual...or in N in an disengage the gearbox.. you see the point there.
Too - noises do "travel" but if you can get / use a mechanics stethoscope and try and pinpoint the area its coming from - or , use a long screwdriver in place of a stethoscope.. that will do the trick... Once narrowed down to an area of the engine, you can usually guess then where its coming from - ie..if its accentuated through the stethoscope on the very top of th eengine - usually its a cam shaft / or valve causing it- then you need to take the top off to check visually.
If its lower down the engine - ie, big ends etc.. thats usually a heavy knock rather than a tapping noise...
Too- if its a pulley causing the problem - or the compressor - the belts need to be removed to see then on start up / engine running (for a short test ) to see if the noise has now gone - if it has, its one of the components that is driven by the belts.. If it has gone, then a close inspection of each driven part will reveal the cause.
You dont say exactly which engine you have - the diesel engine tends to get failure of the main bottom if thats the case, check that...
Working through as above you should get to the bottom of this..
Let me know how you go..and / or let me know if you need anything further on this..
~~~~ Meantime - Please do click on the "Exc / Ok rating" for me at this time.. "Thank you" in advance for that .
.. Note that you can get back to me anytime at all after doing the rating - it doesn't close you out.
-- Best Rgds, MIKE.
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