Weird Humming Noise From Engine After Start

[andrewgrhogg]

Whenever i start my car (1996 328iC) there is this pretty load humming noise from the engine bay for about 3 minutes. Sounds like a fan but pretty sure it is not. Any clues?

[Rooz]

could be your alternator....

[andrewgrhogg]

OK - i spent a little more time poking around inthe engine and timing how long the noise goes for. It lasts for about 2 minutes and then turns off. When i open the hood, standing at the front of the car, there is a black plastic cylinder in the far, rear left corner. It has a corrugated plastic tube coming our of it and running down the left side of the engine toward the front before temrinating in an end cap that has some holes in it. The cylinder also has a rubber tube going from it to the side of the engine block.

Does anyone have any idea what this thing is and why it is making this noise? And is it normal or is it broken?

Thanks

[pcy]

Originally posted by andrewgrhogg@Feb 18 2005, 11:16 PM
OK - i spent a little more time poking around inthe engine and timing how long the
Does anyone have any idea what this thing is and why it is making this noise? And is it normal or is it broken?

[snapback]294648[/snapback]

It's called Secondary Air Pump. Typically, that motor is activated approximately 2 minutes after the start up. Then, it stops automatically. You will see a vavle connected via hose. Due to age, the valve starts to go bad and lets moisture in to the pump. As the moisture damages the motor... the noise you are hearing is that of motor slowly going bad. The noise will gradually get worse. Eventually, you'll have to replace the Secondary Air Pump, the valve, and it's gasket.

good luck