Why the thunderous roar on cold starts?

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Bert_W164

Active Member
Joined
Jul 26, 2014
Messages
265
Location
Berkshire
Car
ML (W164)
Hey,

Not a problem or complaint thread, just wondering why Mercedes cars make such a thunderous roar when started cold, it almost sounds like they blip the throttle, hold it there for a second or two, and crack on as normal.

I'm assuming it's something to do with getting the oil moving along to protect the engine, or is this just one of those things certain line up of Mercedes cars do?

I've noticed my mates CL500 use to do this, my ML does this, and it seems the colder it is outside, the louder it is...

No rattles, bangs, pops or anything worrying, it actually sounds really nice, but caught me off guard the other night as I saw activity in my neighbours curtains and felt bad for waking them up (not decatted or running any weird modifications)
 
Not sure if newer mercs have a viscous fan clutch , but that will make a wind turbine like noise on start up before disengaging
 
Not sure if newer mercs have a viscous fan clutch , but that will make a wind turbine like noise on start up before disengaging
Oh no this is more the V8 singing. Happens below 10c it seems.

@Bobby Dazzler cheers, my mate and I always wondered why they blip the throttle, preheating cats and advertising "I'm a big engine rawrrrrr" seems logical, cheers.
 
Not yet it isn't, but I ordered the decals from eBay :thumb: ;)
Screenshot_20201010-204033__01.jpg

On a serious note, anyone got real world data on how beneficial this feature is?

A part of me wonders if it's worth trying to code it off in star.

Thought behind turning it off is being nice to my neighbours and not blasting it where I park it...with a recent new born I've discovered random journeys at any hour is now a thing... the Audi's farting when changing gears in the back roads to assert dominance and impress mandemz in early hours is enough to want to set those cars alight. I'd rather not be that guy who wakes up the neighbourhood.
 
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What's happening here is secondary air injection. Extra air is injected into the exhaust to help the cats deal with the rich (unburnt) fuel coming through the exhaust from the cold engine.

It ensures the catalytic converters work quickly and prevents them being damaged from the excess fuel.

If you disable this, and on some cars you can just disconnect the air pump or remove a fuse, you might find your catalytic converters fail prematurely (which would cause an MoT emissions fail in the UK).
 
View attachment 103390

On a serious note, anyone got real world data on how beneficial this feature is?

A part of me wonders if it's worth trying to code it off in star.

Thought behind turning it off is being nice to my neighbours and not blasting it where I park it...with a recent new born I've discovered random journeys at any hour is now a thing... the Audi's farting when changing gears in the back roads to assert dominance and impress mandemz in early hours is enough to want to set those cars alight. I'd rather not be that guy who wakes up the neighbourhood.
I used to catch early flights three days a week, leaving home before 0400 and the M156 ML 63 was the quietest modern car we had at the time. Luckily I have understanding - or should I say lovely and tolerant - neighbours! 🙉

On a cold start the M157 5.5 makes the M156 6.2 seem quiet, and the M178 4.0 makes even the M157 seem tame 😳
 
What's happening here is secondary air injection. Extra air is injected into the exhaust to help the cats deal with the rich (unburnt) fuel coming through the exhaust from the cold engine.

It ensures the catalytic converters work quickly and prevents them being damaged from the excess fuel.

If you disable this, and on some cars you can just disconnect the air pump or remove a fuse, you might find your catalytic converters fail prematurely (which would cause an MoT emissions fail in the UK).
Okay, definitely don't fancy prematurely changing the cats on this beast 😅
 
Have a neighbour just a few doors along with an 2015 TT E63. I hear his car start up and it does sound louder than my 6.2 E63. But when my baby opens up and is up to temp, that smaller engine baby gets in its rightful place and let's the big boy do the roaring :thumb:
 
The 55k can be very loud on a cold start as well. But can be near on silent when in motion.
 

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