Long story short, I usually have to pick my lil brother up from school...I sit in the parking lot for about 10 minutes before he gets out to avoid the traffic.
Which uses less fuel, sitting idling for 10 minutes or starting the car up if I shut it off?

 

shutting it off will, since sitting for 10 minutes the engine does not really get cold so basically it is a hot start which does not use that much more additional fuel compared to a cold start, (except for maybe if you are sitting in a snow storm, but that be more comfort issues if anything)

also if you shut off the engine, you gotta be careful not to drain your battery , so you gotta keep the stereo's volumn down and not use electrical accesories too much

 

if 10 minutes radio zaps your battery - its time for a new battery
Note- get battery tested for winter

It uses a few drops of gas either way, fsttyms1 idles his car for hours without issue

The alternator is not turning fast enough below 1500 to charge the battery, just enough to replace whats being drawn by engine running needs

Not supposed to run both seats on High at idle- too much draw from the battery- alt cant keep up with it

Long story short: 6 of 1 half dozen of the other

 

So shutting it off is the better option?
I just chill with the windows open and radio playing, not that loud b/c one of my speakers is blown.

 

yeah if a battery is only lasting that long then yeah you need a battery, the amps especially for a sub/subs can pull quite a bit a power in a short amount of time (30-40 amps easily on decent system), but also discharging your battery repetitive like that (even if it still starts) will shorten the life of your battery dramatically

then it sounds like you will be just fine,
also it always better for the engine if you can prevent excessive idleing (even though fsttyms1 may do it) (oil will last longer too) also think about it this way, you are causing wear and tear on basically one item (the battery) with the engine off, while with it running you are getting wear and tear on hundards of parts, much cheaper to replace multiple batteries then a engine in the long run for the ramble

 

I do it because in a typical day the car would have to start probably 100+ times, leaving it run is far less wear on the starter and other things, plus it just makes my life much easier not having to. (8 hrs of idling wastes less than 1/4 tank of gas, dont ask how i know that) As for oil life that little bit isnt going to hurt a thing. I go 10 to 15k on mine with what i do.

Now for him and the 10 min, of course he will save more fuel, but shutting it off isnt going to necessarily make his motor last longer.

 

these motors will outlast most of us

starter wear, ring gear wear, ignition switch wear and the battery use each time you start vs oiled parts that run together,,

Every shutdown drops all the oil to the pan and restart takes a few seconds to get oil to all the parts and start getting good pressure
The most wear on an engine is startup- that waiting for oil is brutal on those metal parts

 

Battery is ok with recharging from a 10 minute non 600watt subamp use while parked
They are good with that- but dislike full discharge then jumpstart and drive-
The alt going full blast amps into a battery that really needs a slow charge ..then the bigger amps the car puts out to recharge fully

 

wow. 100+ times a day? thats alot of getting in and out of your car. besides the car, hows the back and knees constantly doing that??

 

oh btw... i always turn off my car if i know im sitting for more than 5 mins. 1. save the planet, 2. saves me gas 3. my car isn't moving, why have it on.

 

Rule of thumb is if you're sitting for more than a minute, shut it off.
Saves gas and wear and tear.