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Pete, Mercedes Mechanic
Category: Mercedes
Satisfied Customers: 27814
Experience:  Over 15 years experience as a Mercedes dealer technician
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Marty, tough question for you. Brought my 08 GL450 in

Customer Question

Hey Marty, tough question for you. Brought my 08 GL450 in because it made a rattling sound for 5-8 seconds on start up. Dealer came back with cam adjuster repair needed. Got the car back and the rattling was still there. Took it back and the dealer decided to change the timing chain. Got the car back and rattling sound is still there. After 1 year, the sound is still there. Cold or warm on start up. I mentioned that it sounded like a chain tensioner and I also mentioned that the sound always went away and mentioned that maybe there is an adjuster that is driven by oil pressure and until the pressure goes up the sound is heard. GL runs great, lots of power only a rattling on start up. I have taken it to 2 mechanics and no answer. Don't want to go back to dealer as I assume they will change the engine to make the sound go away..
It really sounds like chain slap and the sound is located on the passenger side front of engine near the timing chain.
What do you think?
Submitted: 8 months ago.
Category: Mercedes
Expert:  Pete replied 8 months ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Did the dealer change out the timing chain tensioner at all?

Let me know so we can continue,thanks Pete.

Customer: replied 8 months ago.
No.said it was fine
Customer: replied 8 months ago.
I have a video of the start up I can send.
Expert:  Pete replied 8 months ago.

If you can send the video this will help.You may have to upload the video to You tube and send me the link to see if.They may have inspected the tensioner and it seemed fine but it does also operate off of oil pressure.If the oil pressure is leaking past this tensioner then it will cause this noise here on start up especially when cold.In some cases you can use an automotive stethescope and listen around the tensioner shown below to see if it loudest when this occurs to help determine if it needs replaced.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

Customer: replied 8 months ago.
I asked that question and they said it was fine. I also read that there was a valve added to the tensioner to stop the oil from leaking out on newer models, not the 08. How would determine if the tensioner is leaking? I have already dumped 3k and the noise is still there. The noise was originally heard when cold. Now I can hear it after the car sits for 1 hour+ in all temperatures.
Expert:  Pete replied 8 months ago.

I believe the only way to tell for sure is to remove it properly and then apply air pressure to the oil feed hole when it is cold to see if it pushes out or if you can hear or see air bleeding past it.I have checked several of these this way before.The pressure pin (1a) in the diagram should push out when air is forced in through the oil feed hole.

This does sound like the tensioner to me from here with what is described and I have seen these fail before.

The other issue is the oil pressure pump.This would need tested with an oil pressure test gauge attached to the engine and when started cold to see if oil pressure is low or non existent right away.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Your 5 star rating is appreciated

Thanks Pete

Customer: replied 8 months ago.
The only reason why I am continuing this question with you is that I diagnosed this originally with the dealer. I told them that I thought it was the tensioner. It sounded just like my chain on my wr450 when the chain slaps the swing arm. I don't understand how a mechanic with this information would repair everything but the tensioner.
When you change a timing belt you usually change the water pump (VW), why would you not change the $100 tensioner when everything was apart and easy to do? I told them to change it but thay said it was OK. Has 110,000 miles on it.
Expert:  Pete replied 8 months ago.

I always try and change the tensioner when doing a timing chain if the customer will allow, as your already in there for one and like you said the part is cheap.I am not real sure why they did not even offer it to you unless they really thought it was o.k. but if they did not check the pressure side of it then it would be difficult to say it is o.k.

Customer: replied 8 months ago.
Is there any where else to look for the fault. Could there be something in the top end that would make this start up noise.
Customer: replied 8 months ago.
Also, do you know what would cause the 40 amp air suspension fuse to blow. The front end is lower this morning and the airmatic malfunction light is on?
Expert:  Pete replied 8 months ago.

Your engine has hydraulic lash adjusters which are just like lifters and also fill with oil.These are also very common to bleed down oil pressure causing this fault here.Normally the noise is heard around the top or sides of the engine with this issue here.They look like this below ( #2).

Usually this fuse will short out when the compressor is either shorting out or drawing to many amps.This would be the air suspension compressor usually needing replaced as well as the compressor relay.This will cause the light you see to come on.

Thanks Pete

Customer: replied 8 months ago.
will the adjuster noise sound like chain slap?
would the adjuster fail because lack of oil? wife ran the car with the oil cap not secured coming back from vegas?
Also, is this noise I here damaging? I think it is related to oil pressure and/or initial pressure build up from a leak.
Expert:  Pete replied 8 months ago.

The adjuster can sound like a chain slap issue here as it does also work with oil pressure.With the oil cap loose this would have not caused a failure like this here.

Usually it isnt damaging but can become worse to where it may be there all of the time.

Thanks Pete

Customer: replied 8 months ago.
I am going to send you the video. then we are done
Expert:  Pete replied 8 months ago.

Sounds good

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