Removing "wind deflector" on 4runner rear window - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

Quattro · 02-13-2009, 09:58 AM

I took it off last night. It is fixed position, and can't be angled. That isn't to say some custom brackets couldn't be made to change the angle!

Out of curiosity, what angle would I likely benefit from having?

Daox · 02-13-2009, 10:00 AM

Even with exhaustive testing I don't think you'd ever see noticeable gains from mounting it perfectly. Not to say it can't be done. My point is there are much easier and better mods to do. A grill block is an excellent example that will return greater FE.

trikkonceptz · 02-13-2009, 11:49 AM

Quote:

Originally Posted by Daox

Even with exhaustive testing I don't think you'd ever see noticeable gains from mounting it perfectly. Not to say it can't be done. My point is there are much easier and better mods to do. A grill block is an excellent example that will return greater FE.

Eh ... 2 weeks of testing my 4-runner netted no gains from a grille block. The likely culprit may be the fact that the vehicle has such a high front profile as opposed to a car. But in the end the complete grille block netted me zero benefit, but also did not hurt my FE.

winkosmosis · 02-13-2009, 03:21 PM

Quote:

Originally Posted by Quattro

I took it off last night. It is fixed position, and can't be angled. That isn't to say some custom brackets couldn't be made to change the angle!

Out of curiosity, what angle would I likely benefit from having?

The best I can do is visualize airflow.. To me it seems that if you angle it at maybe 15 degrees, it will pull down airflow coming over the roof. With that stream of air going down at that angle, it might create a virtual kamm back behind the 4Runner, and air going above the deflector would go down the virtual slope of air.

Or, maybe the vacuum behind the car will suck air through it, and the air would expand and have a decent impact on the low pressure back there, but it would do it without swirling around in a vortice

ConnClark · 02-17-2009, 01:40 PM

Actually this air deflector does help your aerodynamics. They have been putting similar deflectors on the back of school buses to try and improve aerodynamics. I read an SAE paper where they said they could reduce the drag of a bus by about 14% if I remember correctly.

It keeps a boundary layer attached to the back of the vehicle preventing it from becoming a turbulent vacuum. You do get a turbulent vacuum behind the back of the deflector however the reduction of the vacuum behind the majority of the back of the vehicle more than makes up for it.

And as noted it helps keep your rear window clean too

Daox · 02-17-2009, 01:54 PM

Got a copy of that paper handy?

ConnClark · 02-17-2009, 02:00 PM

Quote:

Originally Posted by Daox

Got a copy of that paper handy?

Unfortunately no

lost it when a CD got scratched beyond repair

Edit: And the 14% was on a very very boxy bus

Quattro · 02-17-2009, 08:24 PM

While not an official test, my scangauge says I'm doing a little better without it. Same commute, one day with it on the next day with it off...and a slight increase in overall trip mpg was seen with it off. Since this isn't a perfect test, I'm not going to rely on it, but it doesn't appear to be doing any worse without it.

skibum540 · 05-23-2010, 08:47 PM

It's isn't to keep the dirt and snow off, it's designed to blow air down over the rear window to prevent exhaust from coming into the vehicle while the window is down. When you are driving there is an eddy of air being dragged along behind you. It's what road bikers take avantage of when drafting behind a truck. Once you let that rear window down though, that air (and exhaust) can easily flow into the cabin which has lower air pressure than the eddy behind you.

So if you do remove the rear window deflector, just make sure not to drive with the rear window down. Or if doing so, keep a front window cracked in order to keep air flowing out and not in the rear window.

gasstingy · 05-24-2010, 08:54 AM

Welcome to the site. As for the air deflector, you might see what happens without it. As for me, I'd leave it on. I had a '79 Malibu station wagon years ago, and after I added the spoiler to keep the back window clear, I noted an increase of just over 1 mpg as well. I'm not the aero-expert of the group, but I just figured (at the time) that it forced a little bit of air into an area that was sucking huge amounts of air as a sort of wake.