Rear Window Open and too much exhaust smell

[Liam1234]

ok, I did a search and could find nothing....

This particular design of the 4Runner lends itself to collecting more dirt on the rear hatch/door than one would expect. Not a major big deal except its dirty more often than not.

With the warm air we have been having, I have been driving around with the rear window open and bottom line is no matter what speed, it sucks in exhaust gases into the cabin to the point where you cant drive around with it open for long.

Same thing must be going on to attract dirt to the rear, some kind of air flow/ current back there causing it to venturi up in to the cabin???

I did have the sunroof open each and every time I had the rear window open.

Anyone else finding driving with the rear window open either a hit or miss? and what I mean by that is that you can drive for a bit and all is well and your enjoying the warm air then.... boom, the exhaust hits you in the face and you say, WTF? and close up the rear window.

 

[Johnny Utah]

i've been driving for a few weeks now with my sunroof open and the back window down and i've been fine. Yesterday i drove about 10 miles with all windows, sunroof and back window down and was fine.

Maybe, i'm not driving long enough drives or maybe i need more stop and go traffic, but, i'm not seeing the same results you are talking about.

 

[K O]

Probably has more to do with where you live and the types of other vehicles around you than any thing. Of course, if I pull up behind a diesel belching fumes, I'm going to want to close up my windows or I'm going to have a nasty stank.

 

[Liam1234]

What octane gas do you guys use??

Probably has more to do with where you live and the types of other vehicles around you than any thing. Of course, if I pull up behind a diesel belching fumes, I'm going to want to close up my windows or I'm going to have a nasty stank.

 

[Awynt]

On warmer days, I drive 27 miles from work to home with windows, roof, and rear window open with no issues. Now, if I veer off onto the dirt roads around where I live, I have to close the rear and back two windows, but that's to be expected. Haven't noticed exhaust smell... I use midgrade gasoline if that makes a difference?

 

[scanny]

I don't have exhaust smell with rear window down except of course If there is a school bus or a delivery truck beside me. Use 87 regular. I think that dirt on the back is coming from wheels, not with airflow. By the way with rear windows and sunroof open I feel like I'm in a convertible, it's real good air flow, airpressure should keep fumes far behind I would think. Maybe those fumes came from vents, did you try push recirculated air button?

 

[homeyclaus]

All hatchback and station wagon vehicle body types will draw up whatever is behind them and deposit it on the back of the vehicle because of the lower pressure that forms behind the vehicle as it speeds up. Trucks with cube boxes etc will do this as well. It's how air flows, and that's why there is a wiper back there to remove road spray and whatever else gets on the vehicle from being sucked up behind it.

If only the back window is open, the vacuum that forms at the back of the vehicle extends into the cabin, and whatever is behind the vehicle will get pushed into there. Including exhaust. GM (and I think Toyota too) used to include warnings about carbon monoxide poisoning risks if the vehicle was driven with the back window or hatch open.

If you have the front windows open too, it usually counteracts this effect, and air flows through the cabin from the front to the back.

 

[scanny]

All hatchback and station wagon vehicle body types will draw up whatever is behind them and deposit it on the back of the vehicle because of the lower pressure that forms behind the vehicle as it speeds up.

In that case would be logical to assume that higher pressure in the cabin would push air through the open back window to equalize lower presssure at the back. And theoretically fumes can't go in the cabin. Just a thought.

 

[TrailHawk]

In that case would be logical to assume that higher pressure in the cabin would push air through the open back window to equalize lower presssure at the back. And theoretically fumes can't go in the cabin. Just a thought.

When you open up only the back window, the cabin pressure equalizes to the pressure behind the car (i.e. lower than ambient). To keep fumes out, you would need to maintain that differential somehow as it would decay very quickly. If you could do that, you would be providing thrust

To the OP: I don't have this problem with the tailgate window open in combination with either the sunroof or front windows.

 

[scanny]

When you open up only the back window, the cabin pressure equalizes to the pressure behind the car (i.e. lower than ambient). To keep fumes out, you would need to maintain that differential somehow as it would decay very quickly. If you could do that, you would be providing thrust

To the OP: I don't have this problem with the tailgate window open in combination with either the sunroof or front windows.

Well, I think that air flow in this case would be way more complex but speaking about air pressure I don't think that it's a dramatic pressure difference, and I think it's pretty much limited by the trunk area. Otherwise we either would have our backs in dust from the road or got all our loose stuff out through the back window But it's an interesting thought, maybe one day I tie up piece of paper somewhere in the trunk so I could see it in the rear mirror and try to see what direction air moves.

 

[homeyclaus]

Well, I think that air flow in this case would be way more complex but speaking about air pressure I don't think that it's a dramatic pressure difference, and I think it's pretty much limited by the trunk area. Otherwise we either would have our backs in dust from the road or got all our loose stuff out through the back window But it's an interesting thought, maybe one day I tie up piece of paper somewhere in the trunk so I could see it in the rear mirror and try to see what direction air moves.

Put a smoke grenade or similar device (hint: don't try it with tear gas) on your trailer hitch and drive with the back window open. You'll soon see that your cabin is full of smoke from said device. Sand and road spray don't go as far because they're heavier. Things usually don't fly out the back window through this mechanism, since the air (and what it carries) is moving into the back window, not out. And you're right, it's not a big vaccum, but enough to move lighter things like dust around.

Air movement isn't perfect, it's full of eddies and whirly things, which is how the exhaust smells reach the front seat at some point. Fluid dynamics is a complicated thing.

It's really hard to explain without a diagram. Suffice to say if you drive around with only the back window open in any vehicle of the 4Runner's shape, and you'll smell its exhaust at some point. That includes Tahoes, Pathfinders, Explorers, and square-bodied Buick station wagons, since it's specific to the shape, not the make of the vehicle.

In that case would be logical to assume that higher pressure in the cabin would push air through the open back window to equalize lower presssure at the back. And theoretically fumes can't go in the cabin. Just a thought.

Yes, until the cabin is in the vacuum too when the pressure equalizes. The vacuum behind the vehicle is directly related to the speed of the vehicle - the higher the speed, the higher the pressure at the front, the stronger the air eddy at the back creating the vacuum. Slow down, and the vacuum at the back decreases, and that gas comes from somewhere ... behind the vehicle, exhaust and all. This does not count the other little eddies and whirly things, air density, etc.

Totally theoretically, if you could keep the air pressure at the front of the vehicle completely constant, and therefore the vacuum the vehicle creates by passing through the air at the back exactly the same, and if had no air movement otherwise, and your vehicle did not emit exhaust gas (because it interferes with the vacuum at the back), you would not get any exhaust gas(duh), road dust, or confetti you just drove over into the cabin. Chance of that happening: approximately 0%

 

[Prolex7]

I noticed this today while I was driving a little over an hour on the Interstate with the back window down and sunroof open. I bet there is some type of combination in slightly rolling down the other windows to help keep it out of the cabin. A side-exit exhaust would probably help!

 

[Johnny Utah]

you got me paranoid. Cause now i feel like i smell exhaust or a burning smell, when i have the back open. All was well until you brought it up! damn you! :roadkill:

 

[PracticalFJ]

This has happened on every generation 4runner I've owned. It always happens when I am hard on the gas. Unless you route the exhaust to the side, your gonna smell that lovely exhaust. The dirt however, is just going to happen. That's why I really enjoy the good car washes that have 4-6 people being very attentive to your ride. I like full service and so does my Trail.eace:

 

[4RBob]

I can't remember if it was my 4th Gen's owner manual or maybe a Jeep I had, but it said not drive with only the rear window open because of exhaust fumes.

 

[Japsfinest]

I dated a girl that had a 4th gen and she would roll up all her windows except for the rear hatch window right before she got on the highway, the truck would smell of exhaust and then she would roll all the windows back down to clear the smell. I finally asked her one day what the ritual with the windows was about and she casually responded that there must be a dump or water treatment plant nearby because the truck always smelled bad when she was getting on the highway.

I laughed for a minute when I realized it was not a any of the two choices, it was the exhaust fumes as she nailed it to get the truck up to speed. Once I explained the situation to her she looked at me as if I was explaining the pythagorean theorem. She was blonde anyway...

 

[-JD-]

My 3rd gen used to have a spoiler over the rear window, it would direct air moving over the vehicle down and over the rear window to help counter the air/exhaust coming up from below the vehicle. Too bad they didn't continue this, made a big difference to the exhaust and dust coming in the back vs. my 2nd gen....

looks like this...

 

[harper7]

No clue what your talking about?
We always drive around with the rear window open and never smell a thing???

 

[mhbarber]

2011, smell is unbearable

I know I should take it in, but haven't. I asked the dealership to address the exhaust smell at the 5k inspection, but they didn't find anything unusual. I would love to drive around with the rear window down, but whenever I hit the gas, the smell is terrible. My children won't ride with me when the rear window is down. Sucks.

 

[SeattleMike]

I know I should take it in, but haven't. I asked the dealership to address the exhaust smell at the 5k inspection, but they didn't find anything unusual. I would love to drive around with the rear window down, but whenever I hit the gas, the smell is terrible. My children won't ride with me when the rear window is down. Sucks.

It's a normal byproduct of hard acceleration and the chemistry involved in catalytic converters. In short, the combustion process is less than optimal in most driving situations, allowing hydrocarbons and sulfates to build up in the cats. As temperatures increase or you get a sudden heavy burst of hot gases, a reaction occurs (by design) that converts the hydrocarbons to sulfur dioxide... releasing the rotten egg smell. 4Runners get it the worst because our tailpipes go straight out the back and we have a window that CAN be rolled down and the airflow comes up and into that window when it's down.

The best option is to have a shop bend the exit pipe to the passenger side and put a nice exhaust tip on it.