[scskysc]

Does the N20 engine normally sound like a diesel when it starts first thing based on a "cold" start?
I have 147 miles on my 2012 328i and this morning I started it and it sounded like crap for like a minute before it quieted down and sounded like I expected.

I can understand if the variable valve control is doing something for cold start emissions and producing this noise, but the dealer didn't brief me on this so I'm concerned.

[DR.Nefario]

Yeah it sounds pretty horrible on cold start, it's normal

[Puri1]

yea it does.. it sounds like a diesel... hate that initial sound ...

[Frogman]

Originally Posted by scskysc

Does the N20 engine normally sound like a diesel when it starts first thing based on a "cold" start?
I have 147 miles on my 2012 328i and this morning I started it and it sounded like crap for like a minute before it quieted down and sounded like I expected.

I can understand if the variable valve control is doing something for cold start emissions and producing this noise, but the dealer didn't brief me on this so I'm concerned.

Yes, completely normal. It's due to the direct injection engine design and (I think) the blow-off valve being open when the engine is cold.

[SomeRandomer123]

Stand behind it on a cold start or leave your door open - sounds ace. Not so great from the front...

[CurlyFatAngry]

The only reason I like auto start stop is in traffic lights no one hears that awful sound.

[The X Men]

Originally Posted by Frogman

Yes, completely normal. It's due to the direct injection engine design and (I think) the blow-off valve being open when the engine is cold.

The N55 have direct injection and it doesnt sound like carp when its cold.

[Frogman]

Originally Posted by The X Men

The N55 have direct injection and it doesnt sound like carp when its cold.

I didn't know fish made sounds!

[scskysc]

Good I assumed so, but I just wanted to make sure.

Word to dealers when you sell the car tell your customers about this or they will bring it back and screw up service numbers.
I hate to say this, but at least when I purchased my SKY they gave us a complete walk around of the vehicle on delivery.

Now that I know for certain it's normal I know what is happening and totally understand it. Its high EGT on start to help light off the catalytic converter sooner for emissions reasons.

[r3dbimmer89]

It's due to direct injection

[NAV8TT]

I know it sounds aweful, it's to quiet a twin turbo engine

[pkimM3r]

OP is that a saturn symbol in your profile pic?

[Alexc360]

Originally Posted by Prince300

I know it sounds aweful, it's to quiet a twin turbo engine

Except it's not a twin turbo.

[The X Men]

Originally Posted by r3dbimmer89

It's due to direct injection

I have owned quite a few cars with direct injection, the F30 is by far the worst sounding of them all. I am not so sure its not piston slap like the old GM and Toyota engines.

[scskysc]

Originally Posted by pkim1079

OP is that a saturn symbol in your profile pic?

oh no... I would never do that.. most people probably wouldn't get the reference and consider it an insult..

[scskysc]

Originally Posted by The X Men

I have owned quite a few cars with direct injection, the F30 is by far the worst sounding of them all. I am not so sure its not piston slap like the old GM and Toyota engines.

While I can't say with 100% confidence that I know this to be the case, I can say that with 95% likelihood:

During cold start the Intake and Exhaust valves are controlled in a way that allows for extremely high exhaust gas temperatures to light off the catalytic converter quickly. With direct injection and dynamic valve timing the engine can produce a very rich mixture that is basically dumped out the exhaust valves to the turbo and on to the catalytic. Since the valves are open so long on the exhaust side we are basically hearing the combustion event being spent out the exhaust manifold.
I don't have any definitive documentation on this for the BMW engine, but I know this is basically how GM does it with the 2.0T and 3.6L DI engines. "This results in a smoother operation and an approximate 25-percent reduction in cold-start hydrocarbon emissions during the cold-start and warm-up." - GM Media

Needless to say after my car is sitting for 8 hours in the sun at work, when it starts up it is dead quiet as expected. Only on early morning cold start do I get the diesel noise I asked about originally. I thought I knew what it was from the start, but my wife would have been really mad if I just let it go as normal and toasted her motor..

[adelphi_sky]

I could care less what a car sounds like as long as it drives like a bat outta hell. That's where the real excitement comes from.

[Mahzari]

My car sounds the same. I've also noticed it idles very high in neutral but much, much lower in drive during the cold start. I don't really mind, I just play music off of my USB drive. After 3-4 minutes, it's gone and much smoother.

[The X Men]

Originally Posted by scskysc

While I can't say with 100% confidence that I know this to be the case, I can say that with 95% likelihood:

During cold start the Intake and Exhaust valves are controlled in a way that allows for extremely high exhaust gas temperatures to light off the catalytic converter quickly. With direct injection and dynamic valve timing the engine can produce a very rich mixture that is basically dumped out the exhaust valves to the turbo and on to the catalytic. Since the valves are open so long on the exhaust side we are basically hearing the combustion event being spent out the exhaust manifold.
I don't have any definitive documentation on this for the BMW engine, but I know this is basically how GM does it with the 2.0T and 3.6L DI engines. "This results in a smoother operation and an approximate 25-percent reduction in cold-start hydrocarbon emissions during the cold-start and warm-up." - GM Media

Needless to say after my car is sitting for 8 hours in the sun at work, when it starts up it is dead quiet as expected. Only on early morning cold start do I get the diesel noise I asked about originally. I thought I knew what it was from the start, but my wife would have been really mad if I just let it go as normal and toasted her motor..

But every DI, varible valve timing and turbo engine program works pretty much like that during warm up and they are not nearly as noisy as the N20.
Lets consider the possibility of piston slap for a minute. Piston slapping is usually worst in a engine that use short skirt pistons. BMW's N20 engine use use exceptionally short skirts to reducing internal friction and increase maximum efficiency. Usually DI noise do not quite down as much as the N20 after warm up, but piston slap noise does.

[jwickers]

Yes it could be piston clap... but really hoping it is not.

[The X Men]

Originally Posted by jwickers

Yes it could be piston clap... but really hoping it is not.

Piston slap is totally harmless, it’s more of an annoyance than anything else. Usually piston slap gets louder in the winter time.

[r3dbimmer89]

Originally Posted by The X Men

I have owned quite a few cars with direct injection, the F30 is by far the worst sounding of them all. I am not so sure its not piston slap like the old GM and Toyota engines.

True, but I guess it's a BMW thing. N54 has a slight diesel idle as well but no where near as bad as the N20. The way BMW engineers probably designed the N20 was probably loosely based on some of their DI turbo diesels, of course not completely since diesels only use DI and extremely high compression instead of spark plugs and what not but still could be a possibility....