Bonnet Vent Design Problem causing start knocking.

I have a coupe delivered in Jan 2013 until recently I have had no problems with noisy cold starts untill I started to park it nose forward on the sloping section of my 3 way drive pointing toward my garage door. After it has been left in the rain overnight, on start it makes this horrible knocking/rattling noise for anywhere between a few seconds and up to about 20 seconds, it actually sounds like a bag of nails being circulated in the engine.
Further investigations determine the bonnet vents rain water directly down onto the alternator pulley, when parked at a slight angle the slight well on the engine mount fills up with water and pours over the lip.
When the car is parked horizontal the small casting well still fills on top of the engine mount, but the water that falls over the edge misses the pulley tensioner dropping down to the bottom of the engine bay.
In my opinion this a poor design, if you are going to fit bonnet vents, there should be some way of preventing the ingress of water dropping onto vital engine parts. on the opposite side the vent water drops straight onto the wiring loom, which will probably mean long term reliability problems as the vehicle starts to get older.
I am now parking it back on the horizontal part of my drive(as in the photo), and bingo no more nasty bag of nails starting problems.
I am also in the process of designing some sort of rain/weather protection for the area under the vents to prevent this happening in the future.

I have noticed the same problem a couple of times. Let us know if you invent a solution
Are the vents serving a purpose. if not maybe we could just block them off.
There are no vents on the 5 door so I doubt that they have a function

(19-03-2013 03:05pm)speary Wrote:  I have noticed the same problem a couple of times. Let us know if you invent a solution
Are the vents serving a purpose. if not maybe we could just block them off.
There are no vents on the 5 door so I doubt that they have a function

Squealing pulleys is a problem all round and not unique to the coupe. There is much written about this issue in other threads.

I have had this bag of nails startup once on a damp cold day on my 5dr, so guess it's susceptible to damp conditions, and the vents just exacerbate that, letting further water in, Surely they're just cosmetic, they could only generate air flow, but for what reason? same engine etc. Trouble with blocking them maybe the collection of dirt/debris?

It is not so much squealing, the slippage causes the engine to shake and knock badly (especially loud in the cylinder head area), it litterally sounds like a very loud metalic rattle, I called the dealer and asked about the oil pick up from the sump, and he said that oil pick up from the sump should be no problem at any angle of the vehicle so long as it was filled to the correct level.
Which again brings me back to the vents directing water at a specific angle on to the pulley arrangement for the alternator tensioner, causing it to intermtiitently slip at cold start and setting up the conditions required for this awful engine shake.
In reply to the previous post as far as I can tell these vents are purely cosmetic and serve no useful function, certainly not in Northern Europe anyway.

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Rather than blocking them off from the underneath, as pointed out would cause a build up of debris, I was thinking more along the lines of fabricating some sort of guide for the water coming in to vent it to where it would cause no problems, maybe lower down inside of the engine bay when it can escape from the plastic sump cover.

Having had the car for 16 months and never had this problem I'm inclined to think it has nothing to do with water ingress. After all the car is designed to wade through nearly two feet of the stuff.

I think it is more likely to be a diesel rattle due to cold - they all do that at start up or a loose belt. I'm no expert but I do not see water providing enough lubrication to make a belt slip if it's correctly tensioned.

Sorry to pour cold water on the theory

(19-03-2013 03:18pm)ChuckieB Wrote:  Squealing pulleys is a problem all round and not unique to the coupe. There is much written about this issue in other threads.

There is one other thread on this forum that deals exclusively with this problem, and I am grateful for it too, as it helped me a lot, however nowhere in the thread does it detail that the angle the car is parked at( eg nose down on a slope), makes the water situation onto the alternator pulley system much worse. This is the reason I posted an additional thread on the subject hopefully to help others with this problem. (Incidentally the water filling up on the casting of the engine mount can clearly be seen on the previous thread video)

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(19-03-2013 04:27pm)griff Wrote:  Having had the car for 16 months and never had this problem I'm inclined to think it has nothing to do with water ingress. After all the car is designed to wade through nearly two feet of the stuff.

I think it is more likely to be a diesel rattle due to cold - they all do that at start up or a loose belt. I'm no expert but I do not see water providing enough lubrication to make a belt slip if it's correctly tensioned.

Sorry to pour cold water on the theory

Well congratulations on not having the problem or ever having heard it, I am glad for you, if you had had the chance to hear the problem however and a single iota within you of mechanical knowlege, you would quickly be able to determine the difference between cold diesel rattle and an anomolous mechanical shaking racket at start.
Thank you for your astute observations however and I wish you many more thousands of miles trouble free driving.

I hope you get it sorted soon and can enjoy the same trouble free motoring I have.
all the best.

(19-03-2013 04:44pm)griff Wrote:  I hope you get it sorted soon and can enjoy the same trouble free motoring I have.
all the best.

Thanks man appreciated, I love the car, its a minor issue I am sure I will sort it, as I said earlier when its parked away from the gararge its fine.

My drive is on a slight slope and I have not experienced this problem which ever way the car faces.