I am assuming it helps keep the back of your rig clean because the back of mine gets dirty real quick.

 

the general purpose of a spoiler is provide more downforce on the rear of the car (where the power is coming from) to provide better traction so you won't be slipping around as much. now on an SUV or truck, i dunno who is going fast enough to warrant that or even on the civics i see driving around. more of a looks thing if you ask me unless you're actually going fast enough to use it. if it keeps the rear of the rig clean (i dont know if this is true), that's just a side effect

 

it is for attempting to keep spray off of the back of the window. However, i think its called a rear deflector not a spoiler.

 

i heard it was for keeping the morning moisture and dew off the rear window. it seeems to work for me i guess.

 

maybe its to keep wind noise down when the window is rolled down

 

The rear spoiler/deflector on a 4Runner keeps the exhaust from sucking in the rear window when it is down.

 

i wish i had one on mine, as soon as you crack the rear window thats all you can smell.

 

how does it keep the exhaust out when its on the top of the window? (just wondering don't mean to sound critical)

I read somewhere it was to keep air noise down but I don't know...i think it just looks a lot better with it on...good question

 

Air goes over the top of the 4Runner, hits the deflector and it pushes air down, thus the exhaust fumes do not come up.

Read here for a testimonial: https://www.yotatech.com/forums/f115/1985-4-runner-rear-window-spoiler-91943/

 

like wabbit said it keeps the exhaust from coming into the back window while your moving. It also helps keep water and dirt off of the back window.

My dad has a 3rd gen with the deflector and it makes a HUGE diffrence in rain and dirty enviroments. It has no horrid exhaust smell when you drive with the window down eaither. On my first gen the back window gets dirty much more quickly than the 3rd gen. In adition, if i drive with my rear window down it stinks.

 

true...

 

The above is true, but the actual reason they put them on cars is to improve mileage. It reduces drag by directing air into the vacuum created by high speed air traveling around the car.

 

i don't know if drag is a huge concern with an areodynamic brick like the 4runner but i added a stock one to mine. The rear window does stay cleaner and there is no more exhaust in the rear window.

 

Seems like the exhaust and dirt reason is the winner!

 

On the runner its for the exhaust, on a fwd car its pointless, on a truck unless its a fast v8 itspretty pointless. But on a rwd, fact car it helps create downforce to the drive wheels.

 

Improves gas mileage.
Keeps the rear window cleaner.
Elminates exhaust fumes when the rear window is down.

So which one is more true?

I wanna see the Japanese engineer's notes who designed it so we'll know the exact actual reason.

 

probably would deflect more air if there wasnt a big hole for the 3rd brake light

 

A real spoiler on a race car is to create a downward force using air pressure.

As for the 4runner, its used for something completely different. I thought it was for keeping the rear window clean, but, that seems pretty weird.

Maybe its just for looks, like the hood scoop?

Rabbit seems like he actually did do some reading, and its for an exhaust deflector? Trippy.

So, mine wouldn't do much since I cut my exhaust off ?

 

It's probably not in the engineer's notes at all since marketing probably told them it needs to be on there because it looks good.

 

not entirely true. at high speeds the back of my honda floats around.

now that being said... a simple lip on the rear deck would be suffient. the DC-10 wings i see on the back of civics cause more drag and add more weight than they help the performance of the car. and even with the back thats moving around, nothing will happen with a front wheel drive car, other than making you drive slower, which is probably a good idea.

regardless, beyond the obvious functionality, i think the deflector is also another styling element.