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Tamworthbay

E46 318i auto weird noise

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Had a strange one this morning when I got to work. There was a loud whirring sound after I switched the engine off which I took to be the fan running on. It doesn't usually do that so I lifted the bonnet and the fan wasn't going round. The noise was definitely from the engine bay but not obvious where from. I disconnected the battery and it stopped, after half an hour I reconnected it and no sound. I drove home and no noise when I got back (only two miles).

 

My thoughts are that the fan has popped its clogs and the noise was coming from there but not moving, the time between battery off and on allowed the rad to cool enough. But as it was barely up to temperature that seems a bit weird.

 

Anyone got any other ideas?

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Is it possible there's an auxiliary electric coolant pump which runs on at times?

It is possible but I do t know of one. The drive is very short at about two,miles so can't see how even the fan would activate. I have done about 12,000 miles in it and never had this before. I was hoping it would repeat on the way home so I could disconnect the fan and confirm if it was that or not but nothing.

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Found it! As they say, every day is a school day! Doubt it's that as that would sound in the cabin whereas the sound I had was definitely under the bonnet and if anything front/ front right as you look at it but very hard to track down.

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I've had a few petrol cars that had fans that blew fresh air into the exhaust for the first couple of minutes in the name of emissions. I would expect this to go off with the engine though.

EDIT.  Called an air pump, it seems. My 2000 2.8 Z3 has one now I've looked, not that I've heard it.

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I know you've discounted the blower, however there's loads of stuff on Autodata about A/C issues. One of them states that there's a small movement of the flaps (fnarr!) every time you switch the ignition on/off, and are operated by wee motors. I wonder is one of them sticking on? That said, they're probably not in the engine bay, mind.

 

Other stuff relates to failure of the AC control module. I haven't owned an E46 for a long time, so I don't remember where said module is.

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Main blower Was definitely ok as I could wind it up and down and hear it with no change to the underbonnet noise, but that doesn't mean there isn't another one hiding away under the bonnet I suppose. I will have a look in the (un)trustworthy Haynes manual and see what that comes up with.

 

I am tempted to just jerry rig power to the rad fan and see if that runs or not.

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OK, now bear in mind that this is quite possibly a bum steer. Anyway, some E46s with the N42 engine rated as EU3 have a secondary air pump that can make a whirring noise. Your car might be too old, though. I can post the bulletin. You just pull the relay to disable it, and it causes no OMGEMISSIONSCHAOS. Makes you wonder why it's there.

 

Since I don't really know what I'm looking for, if you'd like an ISO of this Workshop Info System (it goes to 2008) let me know and I'll send you a private torrent link, and leave the torrent up for a while.

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I've had a similar noise on a few cars it was the starter motor whirring along on its own. Disconnect the battery and it stops, the next few times you start it's fine and then another time it stays spinning but not engaged with the ring gear.

 

Can you put your hand on the starter motor to feel if it's turning?

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I've had a similar noise on a few cars it was the starter motor whirring along on its own. Disconnect the battery and it stops, the next few times you start it's fine and then another time it stays spinning but not engaged with the ring gear.

Can you put your hand on the starter motor to feel if it's turning?

Hmmm, that could be it. It's been fine since so will keep an eye on it. When I disconnected the battery it carried on when I reconnected it immediately but not after an hour or so.

 

Did you cure it with a hammer or swap out the starter?

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It did it again today and I have been able to track it down to the secondary air injection pump. When I disconnected the cables the connector was full of water (coolant I think). Google states that this could be down to a failure in the valve which controls it in some way. Both bits are easy to get to, cheap enough to swap out and most importantly make shit all difference to it in the short term.

 

Just wondering why it would run on though? Water causing it to short? Or Ecu having a heart attack because it's failing? No dash lights on with or without it connected.

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