M50 engine hiss noise

[SpidersWeb 0]

Hey guys,

Car starting mis-firing a few days ago, losing 1 and sometimes 2 cylinders, then it just came right and now its perfectly fine. Also recently the check coolant warning came up, and it took about 750ml of water to get up to the cold line, the water was clean and green. So not sure whats going on but it got me interested in the motor and I found this noise. Its a loud hiss and sounds to be coming from near the center of the intake manifold and is loud (louder than the fan and engine itself). Not sure if all of this is related, but thought I'd ask to get your guys thoughts.

It had a BMW Inspection I less than 2 months ago, and has a history of good servicing.

Anyway here is the video of the noise:

http://s83.photobucket.com/albums/j307/DrR...gine_noise5.flv

Thoughts?

[Yuen 16]

Hey guys,

Car starting mis-firing a few days ago, losing 1 and sometimes 2 cylinders, then it just came right and now its perfectly fine. Also recently the check coolant warning came up, and it took about 750ml of water to get up to the cold line, the water was clean and green. So not sure whats going on but it got me interested in the motor and I found this noise. Its a loud hiss and sounds to be coming from near the center of the intake manifold and is loud (louder than the fan and engine itself). Not sure if all of this is related, but thought I'd ask to get your guys thoughts.

It had a BMW Inspection I less than 2 months ago, and has a history of good servicing.

Anyway here is the video of the noise:

http://s83.photobucket.com/albums/j307/DrR...gine_noise5.flv

Thoughts?

Hmm, sounds like a leak somewhere, my car has got a sound too but it's a whistle, said to be the crankcase ventilation valve or breather hoses so I will be replacing them. I couldn't even hear the motor in your video, so I'm not sure how accurate the sound was. Does it go away when you accelerate, ie: does it only occur at idle, or anything else you've noticed?

Btw, 750ml of water is quite a bit to top up, if you do that regularly I would definitely look into it, maybe some hoses aren't tightened very well or the expansion tank cap is not sealed properly.

[SpidersWeb 0]

What I meant about the volume, is that when you stand in front of the vehicle, the hiss heard in that video is louder than the exhaust noise. When driving you can hear both the exhaust and the hiss at equal volumes.

Its quieter at cruise, and louder under full throttle. The tone or volume doesn't changed based on engine revs, and we've poked around and I can't see any major signs of fluid leaks.

On the way home today I noticed its a LOT quieter once the car has actually warmed up.

The car is running slightly worse than it did when we got it (about a month ago), and it has been fed 95 at 98 octane fuel the whole time.

As for the water leak, we haven't owned the car long enough to know, but we do know the coolant warning was not on when we bought it, and it came on about 600km since then. Car has done about 205,000km, so likely something has worn out, but would like to know or have a fair idea about what I"m in for if I take it to a mechanic.

With christmas on the way I dont have a lot of spare cash, but have almost two and a half thousand kilometers to cover before then so kind of itching to know what its likely cause is as I can't afford it to break down over the break.

[isis 16]

check your ignition coils if its misfiring and make sure you DONT have the dreaded Zundspule coils..they're about 150+ each.

[MADBMA 0]

could be a slight crack or hole in the rubber piping from the air flow meter, sucking more air in during acceleration, creating a hissing noise? just a geuss but would also explain the miss firing aswell as you would be getting more air then the onboard computer would be registering.

[Docile 64]

check for cracks or leaks on the intake. it sounds like it has one sumwer

and for the cooling system, ckeck your hoses if they are worn down, do a leak test and see if your car is leaking fluids on your driveway

Edited November 25, 2006 by Docile

[OLLIE 26]

Hmm, sounds like a leak somewhere, my car has got a sound too but it's a whistle, said to be the crankcase ventilation valve or breather hoses so I will be replacing them.

My E30 developed a whistle that occurs when i accelerate, it sounds kind of turbo like. my guesses were injectors, leak in intake hoses or manifold, or someone stuck a vortex in my cold air box.

anyone else have a mystery E30 turbo? what do you think or preferably know what is causing my car to boost whistle on acceleration?

[Docile 64]

i have that as well on my m50. only happens when you accelerate and can be heard on the intake

i think its the natural air suction noise that the engine does when it needs more air on the higher RPM range

my sisters civic has the meanest air suction noise.. even on idle you can clearly hear it.. american vtec FTW hahah

[SpidersWeb 0]

Thanks for the replies

Definately not the air intake, the noise comes from under the intake manifold and the other day it was doing at audibly at idle (as shown in vid). Yesterday it wasnt making the noise at all

My 535i does make an audible air suction noise on accel though, I like that

Oh well thanks for the help guys, I'll just see what happens, its running fine now so fingers crossed!

Edited November 27, 2006 by SpidersWeb

[Docile 64]

get it checked at a workshop.. not at a dealers though..

it mgiht be one of those situations where if left alone can really damage your engine...