Why do I smell exhaust in my van with back windows open?

[FuManchu]

I have a '96 Dodge Ram 1500 with rear windows that flip open a few inches at the bottom.  During the summer I would like to keep them open for air circulation, but when I do while driving, I smell car exhaust fumes inside the van!  The exhaust pipe is at the rear left side of the van.  When I close the windows, I don't smell the fumes.  How is this possible if the van is moving and I'm theoretically leaving the exhaust behind me??

 

[poncho62]

Because as you drive along, a vacuum is created at the back of the van. That is where the exhaust fumes end up and in your windows. It is also why the back windows get dustier than the other windows.

 

[Almost There]

The aerodynamics of a van are creating a funnel at the back of the van for the windows to suck in the exhaust fumes. That's why we always recommend never driving with your rear windows open.

Here's some info on air turbulence:  http://www.explainthatstuff.com/aerodynamics.html

At the very bottom is a diagram of air in motion on a box truck that would be very, very similar to what happens at the back of a van.

 

[Gary68]

 

[GotSmart]

I have a '96 Dodge Ram 1500 with rear windows that flip open a few inches at the bottom.  During the summer I would like to keep them open for air circulation, but when I do while driving, I smell car exhaust fumes inside the van!  The exhaust pipe is at the rear left side of the van.  When I close the windows, I don't smell the fumes.  How is this possible if the van is moving and I'm theoretically leaving the exhaust behind me??

Use the side door windows,

 

[highdesertranger]

this used to be common knowledge. I guess not anymore. never leave your back windows open while driving. this brings up another point, on a computer controlled vehicle you should not smell exhaust. if you do you have other problems. highdesertranger

 

[FuManchu]

Thanks everyone! I've never been all that automobile-savvy, so it's not too much of a stretch for something like this not to be common knowledge for me. I feel a bit sheepishly dumb right now...

 

[highdesertranger]

I didn't mean it that way, but after reading my post it might be taken that way. I am sorry about that. still you really shouldn't smell your exhaust. highdesertranger

 

[akrvbob]

If you can find an air dam that mounts to the very back on the roof, it deflects wind down into the vacuum and theoretically should keep your back window clean and exhaust from coming in.

Anyone ever seen one for a van?
Bob

 

[flying kurbmaster]

you can build a camback if that is what you mean by air dam the idea is this moves air out at the proper angle (12 to 15 degrees) and releases it instead of having it roll back, I got one on my kurb and also one on my Toyota not sure how well they work but windows stay relatively clean ,mpg have improved on the Toyota, you can also use a rear sloping belly pan at about he same angle the idea behind all this is that you create the start of a teardrop and have air move out towards the point instead of swirling around and creating drag. You would never know how well you do exactly unless you had a wind tunnel to test it but can have fun trying.

 

[poncho62]

They used to have those air deflectors on station wagons

 

[highdesertranger]

my 1966 Suburban had those air deflectors in the first pic. they kinda worked at keeping the window clean. highdesertranger

 

[drysailor]

If you can find an air dam that mounts to the very back on the roof, it deflects wind down into the vacuum and theoretically should keep your back window clean and exhaust from coming in.

Anyone ever seen one for a van?
Bob

These folks, http://www.barkow.com/parts_airdam.html make one. It looks like a DIY thing that attaches to an existing roof rack. The only place I've seen rear air dams/deflectors as OEMs, is on some really high-mpg cars, and those look more like a short extension of the upper rear surface of the trunk lid or roof. I want to think that if they really did anything, you'd see them on semi trailers or busses?

 

[eDJ_]

I've considered this for my E 350 high top.  (although I haven't had the issues with exhaust fumes coming in through the tilt out windows at the rear of the Van)  

One piece mud flap mounted to receiver hitch.

The idea is that it directs the faster flowing air under the vehicle down to the ground so it isn't as likely to
swirl upward in the vacuum created at the back of the Van  when underway.   With the front windows open and the rear windows tilted out there is almost a vacuum inside the Van to draw in the outside air.

I've seen these one piece mud flaps made from old pieces of conveyor belt that was purchased for cheap.
(it would probably keep the dust and dirt off the back of your Van too)

 

[Whitey]

It's called the "station wagon effect". When I was growing up, our parents had a '74 Grand Marquis station wagon and there was a deflector built into the roof rack.

http://s1073.photobucket.com/user/A...d/media/Mercury - United States/76D3.jpg.html