Cold engine, loud tapping

Discussion in 'Engine' started by 90salad, Jan 15, 2017.

  1. 90salad

    90salad New Member

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    Hi all,

    This is my first post here - apologies if this has been covered elsewhere but I am having no luck finding any info on this. I've got a loud tapping noise coming from the engine bay of my C280, the engine isn't running and I've been out for a short drive of 5 miles ish tonight, the tapping has started since I've parked up and come indoors. I am parked on a slight decline and I've noticed it doesn't seem to tap when I'm parked on a level surface. Any ideas would be appreciated before I take it to a garage and find out its an easy fix, or even just advance warning of the repair bill. Cheers
     
  2. brucemillar

    brucemillar MB Club Veteran

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    Check your oil level on level ground first.
     
  3. OP
    OP
    90salad

    90salad New Member

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    Thanks for the reply, the oil level is very low and on my list to do today. Have been expecting a few jobs as it's a recent purchase. How could this be causing the tapping?
     
  4. brucemillar

    brucemillar MB Club Veteran

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    If the oil is low? then it will not have enough to circulate around the engine. What you are hearing is likely to be the tappets being starved of oil. They sit on the top of the engine and get the last of the oil.

    Be sure to check the level with the car engine hot/warm. Run it for 10 minutes then leave it for 5 minutes to allow the oil to settle in the sump before using a dip stick or the cars onboard electronics to check.
     
  5. GordonTarling

    GordonTarling Hardcore MB Enthusiast

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    Bruce - as I understand it, the tapping noise is when the engine isn't running, so unlikely to be oil level.

    OP - please clarify when the tapping noise occurs and see if you can listen closely to determine which area of the car it's coming from.
     
  6. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    I don't fully understand the problem? Really you need to be more specific. Topping up the oil would be a good start too.

    You'll get a tapping/pinging noise one you shut down a hot engine. That noise is due to the engine cooling - metals contracting.
     
    Last edited: Jan 15, 2017
  7. OP
    OP
    90salad

    90salad New Member

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    It sounded like the nearside behind a headlight - this morning the tapping was replaced with a whine that varies in pitch, as the ignition is off I guess this is to do with the alarm siren. I sat in idle for a while and then left unlocked, fine after 10 mins spent apologising to the neighbours. I'll still get the oil topped up though
     
  8. brucemillar

    brucemillar MB Club Veteran

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    Whoops. Apologies. Yes it is likely to be the alarm siren gone wonky. Or it cold just be the engine cooling (pinging)

    Apologies again for not reading your post correctly.
     
  9. John Jones Jr

    John Jones Jr Hardcore MB Enthusiast

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    The siren is mounted on the N/s between the bumper and wheel arch. They usually pack up but you can simply disconnect it or remove it as there's only a bracket and a couple of bolts. Remove the N/s wheel and arch liner for access.
     
  10. PobodY

    PobodY Hardcore MB Enthusiast

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    Ah! Is it the sound of an electrical solenoid clicking on and off? - That could be consistent with an alarm that has packed-in.

    The Nissan does this when I've disconnected the battery and the one in the alarm is running down; usually after it doesn't have enough voltage to sound the siren any more.
     
  11. OP
    OP
    90salad

    90salad New Member

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    Great advice guys, thanks a lot for the help. I'll get rid of the siren for a start and see if the tapping continues, in which case it could be the solenoid issue and maybe the alarm as a whole as mentioned above. Will update later on
     
  12. OP
    OP
    90salad

    90salad New Member

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    Didn't have the tools to get the wheel and arch trim off to locate the siren in the end, so pulled the fuse for the alarm system which seems to have stopped the noise issue for now. I'll get a replacement siren and fit it at a mates lockup, in the meantime thanks for the help :)
     
    Last edited: Jan 15, 2017
  13. rorf

    rorf Hardcore MB Enthusiast

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    Probably the alarm back up battery has finally called it quits, unless there is a goblin trying to get out:cool:
     

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