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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > Hood open warning light



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      11-14-2013, 01:00 PM   #1
upstatedoc
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Thumbs down Hood open warning light

Yeah, my E90 doesn't have one. I have a trunk open warning light because that's much more dangerous to drive around with the trunk open.
My detail guy informed me that I was driving around with it open for the last 2 days. Mistakenly popped it when opening the trunk and never shut it. It's very subtle when popped and I never noticed it when walking by it several times.
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      11-14-2013, 01:15 PM   #2
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Good to know .........
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      11-14-2013, 01:32 PM   #3
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Interesting...
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      11-14-2013, 01:54 PM   #4
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I've never had a car with a 'hood open' light, and I've got to disagree that the opening is 'subtle'. I'd be willing to bet that I could reliably identify if my hood was popped or not from 20+ feet with little more than a glance. Maybe try to be more observant?
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      11-14-2013, 02:14 PM   #5
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Quote:
Originally Posted by upstatedoc View Post
Yeah, my E90 doesn't have one. I have a trunk open warning light because that's much more dangerous to drive around with the trunk open.
My detail guy informed me that I was driving around with it open for the last 2 days. Mistakenly popped it when opening the trunk and never shut it. It's very subtle when popped and I never noticed it when walking by it several times.
Yeah, I realized with horror that I was driving with a popped hood a while back. Quickly pulled off the freeway when I realized that. I had popped it to refill wiper fluid and then had forgotten about it. Good thing the safety hook appears to be pretty strong, cant imagine what it would be like if the hood opened completely at 80 mph, but I would guess hood and hinge damage and possibly windshield damage. could be worse if it is at a bad time and something happens before I get a chance to stick my head out the window or look under the hood.
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      11-14-2013, 07:45 PM   #6
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Quote:
Originally Posted by upstatedoc View Post
Yeah, my E90 doesn't have one. I have a trunk open warning light because that's much more dangerous to drive around with the trunk open.
My detail guy informed me that I was driving around with it open for the last 2 days. Mistakenly popped it when opening the trunk and never shut it. It's very subtle when popped and I never noticed it when walking by it several times.
Buy a E30 and you won't have to worry about it.
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      11-14-2013, 08:06 PM   #7
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i could be wrong but i believe i read somewhere that it is a feature of the vehicles equipped with an alarm system?
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      11-14-2013, 08:14 PM   #8
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Originally Posted by wwc310 View Post
i could be wrong but i believe i read somewhere that it is a feature of the vehicles equipped with an alarm system?
This...
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      11-14-2013, 09:59 PM   #9
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My gen6 camry use to tell me this after driving a few feet with the hood open.
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      11-15-2013, 03:40 PM   #10
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so the car is supposed to make up for your mistake of pulling a lever instead of pushing a button?
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      11-15-2013, 03:43 PM   #11
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The car has 3 latches, I've been in a M3 on a track without the hood properly closed bouncing up and down at 140 and it was fine.
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      11-15-2013, 04:38 PM   #12
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If you popped the hood it could never fly up while driving.
1. It's latched
2. It weighs a lot and the wind could never open it
3. Most people can tell visually.

I suppose that's why companies don't put a sensor on some cars. Who knows? The trunk is important cause you wouldn't want the dead body falling out while driving. There's a whole new set a problems that comes along with that!
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      11-15-2013, 04:40 PM   #13
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Quote:
Originally Posted by Eddien123 View Post
If you popped the hood it could never fly up while driving.
1. It's latched
2. It weighs a lot and the wind could never open it
3. Most people can tell visually.

I suppose that's why companies don't put a sensor on some cars. Who knows? The trunk is important cause you wouldn't want the dead body falling out while driving. There's a whole new set a problems that comes along with that!
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      11-16-2013, 02:56 AM   #14
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Quote:
Originally Posted by Eddien123 View Post
If you popped the hood it could never fly up while driving.
1. It's latched
2. It weighs a lot and the wind could never open it
3. Most people can tell visually.

I suppose that's why companies don't put a sensor on some cars. Who knows? The trunk is important cause you wouldn't want the dead body falling out while driving. There's a whole new set a problems that comes along with that!
are you sure about this....? 1 and 3 are fairly accurate, but 2....
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      11-16-2013, 11:32 AM   #15
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Quote:
Originally Posted by JamesAC83
Quote:
Originally Posted by Eddien123 View Post
If you popped the hood it could never fly up while driving.
1. It's latched
2. It weighs a lot and the wind could never open it
3. Most people can tell visually.

I suppose that's why companies don't put a sensor on some cars. Who knows? The trunk is important cause you wouldn't want the dead body falling out while driving. There's a whole new set a problems that comes along with that!
are you sure about this....? 1 and 3 are fairly accurate, but 2....
You would need a lot of speed. A drive on a 40mph road wouldn't do it.
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      11-18-2013, 02:35 PM   #16
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Quote:
Originally Posted by Eddien123 View Post
You would need a lot of speed. A drive on a 40mph road wouldn't do it.
a short highway drive could most definately...
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      11-18-2013, 03:26 PM   #17
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Quote:
Originally Posted by JamesAC83
Quote:
Originally Posted by Eddien123 View Post
You would need a lot of speed. A drive on a 40mph road wouldn't do it.
a short highway drive could most definately...
Eh maybe who knows
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      11-18-2013, 03:52 PM   #18
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Quote:
Originally Posted by Eddien123 View Post
Eh maybe who knows
Sounds like a physics problem!
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      11-18-2013, 04:48 PM   #19
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The hood is pried up by the negative pressure that forms by the wind going over it. That will provide the initial lifting force on the hood. If we assume a uniform negative pressure of around .04 psi (a little digging and found this which is close http://www.alfabb.com/bb/forums/alfe...ml#post1195953) and assume a hood size of about 10 feet by 6 feet (giving an area of 8640 square inches) you get a total lifting force of around 350 lbs!

Once the hood starts to open you need to consider the effect of the wind on it. This is normally expressed as dynamic pressure.

To obtain the dynamic pressure at a given air speed (assuming STP) you use the equation: p = 0.0032 * v^2

Where p is in lbs/ft^2 and v is in MPH. Doing the math you get a dynamic pressure of .08 psi.

With our previous area of the hood we found to be 8640 square inches. It will not be completely flat to the wind but say it is only presenting 30% of its area when the wind really starts to catch it. That would produce a further lifting force of 200 lbs. As the hood comes fully open it would present the full area to the wind and generate a force of close to 700 lbs.

The ultimate result is that your hood is press-formed over your windshield and roof, shattering your windshield in the process typically. Here is an example of what the driver is presented with when this happens: http://www.youtube.com/watch?feature...&v=roLry3b64Xs

Bottom line, make sure your hood is properly closed and latched.
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      11-18-2013, 05:05 PM   #20
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my e90 (2010) 335xi does have one and it's the most annoying thing ever...only cause I installed a strut bar and I need to reinstall it cause it isn't fully right. It's a little higher than it should be and touches the hood I guess and the car always thinks it's open...but it isn't...bahh
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      11-19-2013, 02:59 AM   #21
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Quote:
Originally Posted by Eddien123 View Post
Eh maybe who knows
have you seriously never heard of a hood opening and hitting the windshield? I really can't tell if you're being serious or not... I'm hoping you're being sarcastic at this point...
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      11-19-2013, 12:48 PM   #22
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Quote:
Originally Posted by JamesAC83
Quote:
Originally Posted by Eddien123 View Post
Eh maybe who knows
have you seriously never heard of a hood opening and hitting the windshield? I really can't tell if you're being serious or not... I'm hoping you're being sarcastic at this point...
Eh maybe who knows
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