Not only CO2, but sand! Here in Florida we only have sand, not dirt. Driving down my friends unpaved driveway got a huge amount of sand in the back window. Going slow at that! Only drive with it down sometimes, just about a few inches.

Some of the Kidde Nighthawk models, about $30, have a 9V battery backup if you want to measure levels up front, or use the outlet in the back if you just want to get a reading at the window.


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I usually just run the back window down 6-8" and open the sunroof. You get that convertible feeling without all the wind turbulence in the car. I can drive for a long time like this, especially on summer nights.

I am thoroughly impressed with the lack of buffeting when only the back window is open. You can’t even hear the difference:


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This has been discussed on numerous occasions over the years. Owners with young children or pups who like to ride w the cargo rolled down, will have an exhaust shop turn the tail pipe right behind the right rear.

This seems to be the only solution. Of course when your stopped the fumes can and do get in, but that can happen w most vehicles.

I got accustomed to driving with the window down in my Tundra but the exhaust was aside exit and much further away due to the bed I never had this issue.

In the 4 runner it’s almost unbearable with the exhaust fumes. I pretty much only roll it down the first 3-5 minutes in the summer when it’s super hot inside to vacate all that hot air.

It’s also proved every time we leave the pavement or go off roading. That’s why the back of our T4R’s are covered in dust and dirt. You also prove it every time it rains. That’s one reason why there is the rear wiper.

That said, in autumn (too windy in spring around here), on sunny afternoons, it is quite pleasant to roll down the road with all windows lowered. Minimal turbulence and surprisingly quiet. With all windows rolled down, I’m comfortable with the minimal CO risk.

I’m also old enough to remember riding in the rear facing back seats of early 1960s American station wagons with the back windows open; factory or aftermarket AC was a luxury in those days and somewhat rare. I also remember riding back there with a friend whose family had a Studebaker wagon that had a sliding roof that opened up the entire rear of the car, getting quite sunburned in the process.

Driving with rear window down in California could cause cancer.


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Pretty sure they have a warning label for that.

My dog will be very upset at this news because he rides looking out the lowered back window about 90% of the time. Other 10% is split about evenly between looking out the lowered side window and slobbering all over my center console. I see some funny looks from drivers following who he is is just sitting there staring at.

thinking of going custom just to route to the side.. how effective would a re-route be?

I've set up a carbon monoxide from my house in the trunk just to test for the gas and its never sounded off.... so i trust i wont die but the fumes cant be good in the long term..

haha those were fun except i'd get such a headache from the motion and staring straight out the back window

im gonna get crap for this but i wish everyone and their mothers required emissions testing..

i used to enjoy driving w/ windows down but these stupid ass modified diesels ****in ruin it for everyone

ill chime in w/ my experience.. i did exactly as you guys mentioned.. my monoxide monitor doesn't display levels it just chirps. I never got an alarm for monoxide but the fumes usually force me to shut it early..

but who knows w/ these devices? Who knows if it really works? I've never introduced it to conditions that would/could trigger it.

Someone had it done on the cheap and it seems to have worked for him. I think the main concern is when sitting but could be when driving too. Proof would be all that dirt that likes to collect on the rear window.