Is it bad to cruise around in neutral?

I have an 04 325ci 5pd...I was wondering if any of you in the course of your daily commutes put the car in neutral and just roll down a hill or something? Is this bad to do over a the course of a long hill?

Let me explain for example a part of my daily commute is getting out of a valley, so I drive uphill for like 2 miles and then once i get to the top, I just put it in neutral and let gravity do the rest. (for those of you in SoCal Im talking about the Sepulveda Pass going south on the 405 from the 101) Now this stretch of downhill is about 4 or 5 miles for me and i notice that my temp guage drops from dead center to the white line on the left. This is never an issue if I do it on surface streets like as Im coming to a light because it never lasts long enough.

Is it bad to be doing this? Should I just leave it in gear while im rolling downhill?

sounds like a you need a new thermostat. the temp guage should remain in the middle regardless of how long you roll down the hill in neutral (assuming your motor is not turned off). also rolling down a long hill in neutral will use more gas and wear out your brakes more.

i read something here a long time ago about it being bad over long period of time, but I don't remember. :/

well it really depends, do you have a manual or an automatic? You don't necessarily need a new thermostat, simply your engine is not under any load and not revving up to switch gears and it's creating less friction and making less explosions than if youd be driving it on a normal road. What your forgetting is that your car is still getting air rammed through the radiator cooling the coolant running through the engine, it's perfectly normal, if you don't trust me ask any other mechanic/ tech.

Rolling down the hill is possible and saves a bit of gas, but is generally not recommended for safety reasons- takes longer to stop the car in case of emergency. I like the Sepulveda pass, drive there a few times a week, but always in gear.
I do roll to red traffic lights though, especially to those I know well.

I think a person would have a hard time making a case that it could do anything harmful.

You might try checking your mileage in neutral and in 5th gear by reseting your trip computer at the top of the grade. I would bet that you get better mileage by leaving it in 5th and coasting.

It's called hypermiling. And it's not going to hurt anything

Originally Posted by justin0o

i read something here a long time ago about it being bad over long period of time

Man where do you come up with this sh1t? Too funny. My whole office laughed. Thanks.

I have a manual tranny my previous car was an auto and so I never noticed this before. As far as what tehsex said, thats what I was thinking that because the car is pretty much just idling while traveling at about 50 mph the cooling system is cooling faster than the engine is producing heat.

Im not concerned with safety too much as I keep safe distance and I dont imagine the car would ever just turn off. As fas as fuel economy goes...well my commute is about 20 miles with about 4 miles being "free" so over the course of a long time, I would imagine this would save at least 10-20% of fuel in my daily commutes. Now i dont know how much fuel is consumed when u simmply leave it in gear and just roll but could doing that over the course of 4 or 5 miles be bad for any engine components or tranny/clutch to be working because of kinetic energy of the car instead of gasoline?

It seems like a case could be made for both :/

well i dont think that rolling in neutral will save much gas... maybe even waste more because when you roll in gear, the cars speed is bringing up the rpm's, but when you put it in neutral the engine has to use gas to keep it at idle. Maybe im wrong. Just what i think.

bad thermostat

Originally Posted by tehsex

well it really depends, do you have a manual or an automatic? You don't necessarily need a new thermostat, simply your engine is not under any load and not revving up to switch gears and it's creating less friction and making less explosions than if youd be driving it on a normal road. What your forgetting is that your car is still getting air rammed through the radiator cooling the coolant running through the engine, it's perfectly normal, if you don't trust me ask any other mechanic/ tech.

A modern gasoline car should always maintain operating temperature during normal use (idle, coast, city, highway) especially the electronic thermostat equipped BMWs. Furthermore this is California so it should definitely stay in the middle. I can idle my car in -13F or more(-25C) here in Canada and it will stay right in the middle as it should. This is crucial for proper lubrication, fuel economy and combustion. Definitely sounds like a bad thermostat.

Originally Posted by R1killa

A modern gasoline car should always maintain operating temperature during normal use (idle, coast, city, highway) especially the electronic thermostat equipped BMWs. Furthermore this is California so it should definitely stay in the middle. I can idle my car in -13F or more(-25C) here in Canada and it will stay right in the middle as it should. This is crucial for proper lubrication, fuel economy and combustion. Definitely sounds like a bad thermostat.

If my thermostat is bad, wouldnt it cause overheating (even minor) while going up hills or in traffic? If its ever not in the middle, its to the left. Iv never ever seen it move right from dead center even in traffic, a/c in the LA heat (this summer was HOTTT!!!) I have CPO so maybe I should get it checked out?

i was just wondering this, i also just got my first manual and its little things like this im still scratching my head too

it you were in 30 degree weather coasting for that long, i would say no way to the thermostat problem, however being in LA or wherever it is, i'm sure its between 70-80 degrees out there. With those temps, i find it hard to believe your temp gauge moves, however i could be wrong...

as far as saving gas... coasting in a high gear compared to your engine keeping the car in nuetral is such a minute difference i highly doubt that you would see any difference at all

Originally Posted by Mynewbimmer

If my thermostat is bad, wouldnt it cause overheating (even minor) while going up hills or in traffic? If its ever not in the middle, its to the left. Iv never ever seen it move right from dead center even in traffic, a/c in the LA heat (this summer was HOTTT!!!) I have CPO so maybe I should get it checked out?

if your thermostat is stuck open, your engine will drop in temperature at higher speeds because the air is cooling it down so much faster. My therm was stuck open and my car heated up fine, however as soon as it got some cold winter air in there at 50-60mph, my engine temp dropped

if your thermostat is stuck closed, then it will overheat unless you are going fast enough for the air to cool your engine down

Originally Posted by Mynewbimmer

If my thermostat is bad, wouldnt it cause overheating (even minor) while going up hills or in traffic? If its ever not in the middle, its to the left. Iv never ever seen it move right from dead center even in traffic, a/c in the LA heat (this summer was HOTTT!!!) I have CPO so maybe I should get it checked out?

Depends on where it is sticking.

Stuck open = constant flow of collant from the radiator = running colder
Stuck closed = no flow = overheat

My dad's explorer has a stuck open thermostat and he chooses to ignore it... Poor motor hasn't gotten up to opperating temperature in over 3 years...

If I'm getting it right, going in neutral downhill on Sepulveda pass during commute hours will only make you use brakes a lot more frequently and harder. If any gas can be saved this way, it will not be much and certainly won't even compensate the increased spending on brake pads and rotors. If you want to increase your gas mileage, try to shift in higher gear to avoid high engine revs and drive in a way that will minimize braking... cheaper, but not fun. :-)
Keep your tires properly inflated. High performance tires that provide a lot of traction (wide and soft) are going to decrease the mileage too.

Originally Posted by huggy1989

i was just wondering this, i also just got my first manual and its little things like this im still scratching my head too

best to just keep it in gear and keep control of your car

like others said, if you have to brake hard for whatever reason, the friction from being in gear will make you slow down faster... that alone is a good enough reason to keep it in gear

the only time i used the clutch or neutral is if i come to a stop... i'll down shift usually to 3rd gear (sometimes 2nd) and when i come to 10mph i'll either just keep the clutch in, or throw it in neutral

Originally Posted by snowcatxx87

Man where do you come up with this sh1t? Too funny. My whole office laughed. Thanks.

:p