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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 05-06-2013, 06:40 AM   #1
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Is there any issue with driving without bottom cover plastic?

After valve cover replacement I sprayed down engine last night to remove all the grime from the leaking valve cover. I was planning on driving for a while with the bottom cover off to see if there are any drips, which I do not expect. I did bottom out all of the bolts and the gasket was aligned as expected.
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Old 05-06-2013, 07:02 AM   #2
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Old 05-06-2013, 07:03 AM   #3
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Mine disappeared a LONG time ago. I haven't seen any issues. I actually kinda like it since I don't have to take it off every time I want to work on the car. It does kind of make it easier to detect drips
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Old 05-06-2013, 07:11 AM   #4
Julioalberto236
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I used to use it like that but a friend td me that rocks or any other thing could go up my engine in the highway and i stopped using it like that
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Old 05-06-2013, 07:38 AM   #5
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Is there any issue with driving without bottom cover plastic?

As long as you don't run over a deer your good.


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Old 05-06-2013, 07:44 AM   #6
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I don't have mine either. But will probably get one simply because sand and road crap getting kicked into the engine bay can't be a good thing.
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Old 05-06-2013, 07:49 AM   #7
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It will be going on once cleaned and

once it is determined there are no drips, and I was hoping to dislodge the socket that fell into the engine compartment.

I also realized mine was barely on with many screws loose.
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Old 05-06-2013, 07:54 AM   #8
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I forgot to put mine back on after re-doing my cooling system haha
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Old 05-06-2013, 07:56 AM   #9
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Cars never had undertrays until the last 15 or 20 years. It's mainly just for aerodynamics and it does help to keep it a little cleaner.
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Old 05-06-2013, 07:56 AM   #10
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With the hpf turbo kit we can't run that cover, however I wish i could, it kept the engine cleaner with less upkeep. I also have had since removal a rock or something come up while on highway, hit fan....punch radiator......and put a dent from under the hood out. Sucked. The reason there was a dent is because I had removed the heat shield because methanol had torn it apart.

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Old 05-06-2013, 09:14 AM   #11
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Mine doesnt have it anymore. I found that out when I was checking my car for leaks. To my surpise my car wasnt wearing any panties. And it dawned on me that my car had been to my indy shop for an FSB job a week ago. The shop, ie the mech stole it! I guess he needed one for his car or it'd end up on craigslist.
I called the shop to ask if the mech may have forgotten to put it back on. After putting me on hold for a minute or two the service rep behind the counter said NOPE, the mech said he put it back on. And there was No underbelly shield anywhere in the shop. Yeah right!
PAY ATTN to your mech when he's finishing up any undercar work. some mechs do steal good parts and little things from owners' cars.
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Old 05-06-2013, 02:21 PM   #12
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Without it a rock can get stuck in one of the pulleys and shred your belts.
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Old 05-06-2013, 02:50 PM   #13
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Those claiming damage can occur are really stretching it. That is extremely unlikely. The cover is really for wind noise/aerodynamics and it also keeps your driveway clean. Cars ran without them for decades just as low to the ground as we are. They were always fine.
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Old 05-06-2013, 02:56 PM   #14
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Just because something runs "fine" doesn't mean it's actually running fine. The design to the car is deliberate and function must be considered. It's been widely reported by respected members of other forums that the undertray aids in cooling efficiency as air enters the front bumper and passes through the radiator. Without that cover, you may be pushing the upper limits of your cooling system without even knowing it.

Just purchase one. I would never ever drive our cars without one. It just screams "I can't afford to drive a car" when you're missing large components like that. Plus less dirt and debris for the belts to deal with. Don't forget excess water, noise, drag, etc. Just absolutely no reason to run without it
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Old 05-06-2013, 02:59 PM   #15
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Just because something runs "fine" doesn't mean it's actually running fine. The design to the car is deliberate and function must be considered. It's been widely reported by respected members of other forums that the undertray aids in cooling efficiency as air enters the front bumper and passes through the radiator. Without that cover, you may be pushing the upper limits of your cooling system without even knowing it.

Just purchase one. I would never ever drive our cars without one. It just screams "I can't afford to drive a car" when you're missing large components like that. Plus less dirt and debris for the belts to deal with. Don't forget excess water, noise, drag, etc. Just absolutely no reason to run without it
Yeah...no.

I do agree with just getting one, because it makes the car complete, but the above statement is kind of ridiculous.
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Old 05-06-2013, 03:15 PM   #16
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Yeah...no.

I do agree with just getting one, because it makes the car complete, but the above statement is kind of ridiculous.
It's consensus among veterans of other forums from close to or more than half a decade ago. If air can't move over the radiator as intended, then you have no cooling.

IIRC, the theory was (as confirmed by some engineers in the discussion) that the absence of that tray disrupts the low pressure zone at highway speed which prevents air movement as intended. I forgot the link but there was quite a few discussions on it back in the day.

Edit: Here's one take from an OG. I believe he's on this forum as well.

http://www.m3forum.net/m3forum/showp...9&postcount=35

If you google it, it's common knowledge undertrays aid in cooling efficiency. Remember, WDE, if I say something, there's probably a solid reason behind it. Discussions have been going on long before you came into the E46 world last year.
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Last edited by Mango; 05-06-2013 at 03:22 PM.
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Old 05-06-2013, 03:26 PM   #17
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Mango is right.

Without the cover, the air cannot be forced into the radiator core efficiently and thereby decreases heat transfer efficiency. With the air now being tunneled underneath the car you're essentially cooling the control arm bushings which could in turn give the entire frame a cooler temperature and ACTUALLY AID in the cooling system!!! What a twist!
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Old 05-06-2013, 03:32 PM   #18
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Mango is right.

Without the cover, the air cannot be forced into the radiator core efficiently and thereby decreases heat transfer efficiency. With the air now being tunneled underneath the car you're essentially cooling the control arm bushings which could in turn give the entire frame a cooler temperature and ACTUALLY AID in the cooling system!!! What a twist!


Of course I'm right. I'm Mango.

WDE is waiting for his moment to take me down lately by the tone of his posts
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Old 05-06-2013, 03:38 PM   #19
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I tried to start my car without my undertray today. It exploded in a ball of fire. I put the tray back in, hoping that will fix the issue.
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Old 05-06-2013, 03:41 PM   #20
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Originally Posted by Mango View Post


Of course I'm right. I'm Mango.

WDE is waiting for his moment to take me down lately by the tone of his posts
No no. I just very much disagree with this and a few of the things you've been staunch about lately. You know I agree with most of your principles, but you have a bit of a "catastrophic tone" about some of your recommendations.

I don't think it disrupts air flow significantly enough to hurt cooling efficiency in any meaningful way. Am I going to run without it? No, not if I have one on hand. Would I run without it in the middle of Alabama summer if I lost mine for some reason until I could get a new one? Yes, without hesitation or worry.

I really don't care what some of the vets think about this one. Some things I consider the veteran opinion (and take it seriously) such as on product brands and what you should buy OEM on. That sort of thing. This one comes down to complex aerodynamic interactions that no one here can really even speculate about. The fact is, the radiator has more than enough capacity to keep the engine cool, even if the efficiency is hurt slightly. At most, the fan may need to stay on to a higher speed than usual.
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