Okay. There is a steak dinner at Ruth's Chris Steakhouse riding on this so your answers are important.

When I come to a stop at a light or I am apraoching a line of stopped traffic, a freeway exit ramp or a long downhill road for example, I shift into nuetral and coast [but never under the speed of the trsffic flow] until either I stop or need to acceleratre again. My wife says I am harming the transmission. I say that I am saving gas and coasting in nuetral does nothing of harm to the vehicle.

She also says that when I leave accessories such as AC, radio, etc. I am shortening the life of the battery because it it taking more power to start it. I say these are automated systems and designed for the load.

Her information is based on her dad who owned a auto spring and welding works in the '60's and 70's. I told her that it may be true for older cars but for someting modern made in the past 20 years or so it is unceccasy to turn everything off when shutting the car down.

Opinions? It would be great to hear from a mechanic.

 

I'm assuming that you have manual transmission? I used to coast in neutral from time to time when I had a stick tranny car and I'm pretty sure it does not harm the tranny as long as you rev match when you need to accelerate again. It might be even better on the tranny (marginally) since it puts less load on the tranny over the course of the drive.

Cars these days are designed much better than 30-40 years ago so leaving accessories on doesn't matter. The battery recharges itself when your driving anyways.
I'm not a mechanic but my dad is and has been for 20+ years and he does the same things you do

 

As far as the coasting thing...all that sticks in my mind is that the car, with the engine running and pumping your warm lubricants and coolants through the car has no adverse effects on the car.

As for the battery, how would one determine that the life of the battery is being shortened...how long exactly does a battery last?

Not sure any of her argument holds water.

 

My guess is that you wouldn't hurt the transmission, but would probably wear your brake pads out prematurely. I'm thinking leaving in gear lets you use the engine and transmission to help stop the vehicle. I'm assuming this is a stick, not an automatic?

On the radio and A/C, I don't think it matters much, the car's computer should know what's on and adjust for it.

Cheers

 

Not a mechanic. Leaving it in nuetral and coasting won't harm the tranny (it probably won't save gas either since the engine is still running--think about that).
Starting the car with additional load on the battery won't shorten its lifespan IMO. If the thing is borderline shot it may a start with stuff off vs stuff on though.

 

Yep, coasting in neutral when slowing down/stopping doesn't harm your tranny in any way. Just wears out your breaks faster. So, prefer to save a little gas and replace the pads/rotors a little earlier ? No problem.

Leaving the radio and other electronics on when you shut off the engine and then restart it ? No problem. The battery is going to last just as long as if you turned everything off before you shut her down.

Now, please don't slap the wife. Just tell her we told you she's wrong.

 

From mileage obsessed diesel heads on another forum, I've read that coasting--foot off the throttle--in gear in a standard shift car uses less fuel than coasting in neutral.

 

Newt, it's going to save a LITTLE gas. Those ten seconds or so running at idle (1200 RPMs?) is easier on the gas tank than having the transmission engaged and pulling 2000-3000 RPMs.

Anybody that says differently, I would like to hear the logic behind their position.

 

I don't see how that is possible.

 

I think you are the correct one in this case. Sorry wife -

Donna

 

First things first, I do not condone slapping a female, period.

At idle, the TB has to stay open to prevent stalling, the car will have to pump gas in. When the car is in gear the momentum keeps the car from stalling the TB can close all the way, no air entering in while not under load, no gas being burned coasting in gear.

Also it's safer IMO to leave the car in gear and coast because it gives the driver more options as far as slowing down or speeding up to avoid a collision while the car is in gear in the 3-4k rev range.

However coasting in neutral at speed does not harm the transmission.

As far as accessories, getting shut off, the factory battery is not a deep cycle, so it does not get fully recharged but instead looses a little capacity each time. After about a year I did begin to notice a significant change in time it took the battery to start the car if the accesories were left on,and it only gets worse over time until I replace the battery with a deep cycle one. However this is merely anecdotal evidence. I lack the #s to back this up. Besides, having the radio on when you start the car distracts form that wonderful engine note

So maybe she owes you dinner, and you owe her dessert?

 

I dont think it saves gas at all. If youre not on the accelerator at all, the mpg gauge says 99. So coasting in neutral just has the effect of being harder on the brakes. I used to think the same, and coasted in neutral, but i wore out my brakes much faster. Now i use engine breaking and dont notice any change in mileage. I dont see why it would after thinking about it. Even if the revs are high, as long as youre not accelerating the injectors arent squirting in that much fuel, thats why the revs are slowing.

As for the original question, if youre coasting in neutral you arent harming the transmission, youre not engaged into it. And im not sure about the battery, but i would imagine its not significantly more wear.

 

[quote=CR&PW&JB;2225409]Yep, coasting in neutral when slowing down/stopping doesn't harm your tranny in any way. Just wears out your breaks faster. So, prefer to save a little gas and replace the pads/rotors a little earlier ? No problem.

I am not sure I see how this wears your pads/rotors faster. I don't engine brake anyway. It seems that would put more stress on the engine/tranny. Besides. a shoretened pad/rotro life for me is not an issue since it is all covered for 100, 000 miles.

 

Motor On is right on about the TB and coasting/staying in gear. technically staying in gear would save a little bit more gas than coasting in neutral. but the difference would be so little it probably doesn't really matter. in the old days it was recommended (or even required) to not coast in neutral 'cuz it take more effort and time to shift in gear if an emergency situation arises. that's not the case w/ modern clutch/tranny anymore. my preference is to take it out of gear when i know i'm gonna stop pretty soon 'cuz i *feel* that wear on the drivetrain would be minimized over time that way. this obviously depends on the situation and there're times when engine braking is helpful

as for the battery, i have heard, from opinions authoritative and not, that technically leaving everything on doesn't matter. but i still turn off all accessories before shut off as a force of habit; it just makes me feel sloppy otherwise. i like to be meticulous w/ my cars. plus, technically chemical batteries, such as car batteries, are supposed to last forever

and don't slap your wife

 

if you have an automatic, I'd avoid it as the sudden power application could cause some issues. If you have a manual, if you are coasting to a stop, then OK. If you are costing and then will shift into a new gear later, then it could cause extra wear on the syncros if you don't rev match. Also there could be laws in your area about the vehicle always being under power for control and accident avoidance.

That being said on all my stick shift cars, I do put it in neutral if I am going to a stop as brakes are cheaper than a clutch or syncros if I downshifted through the gears....

Now if you are simply clutching in and holding it to go into neutral well then shame on you as you are wearing out your throw out bearing which only should have something like 40 hours total life span.

 

When slowing to a stop, have you considered leaving the car in gear all the way to a stop then putting the car in neutral without clutching? You get some engine braking and if you pull the lever into neutral right at the normal engine idling RPM is just pops out of gear as smoothly as can be. Its a little harder to time on fast stops or from second gear, so I just clutch in those situations. Of course, that might send your wife completely over the edge...

In the interest of full disclosure, I should say that I don't drive a Mini yet, but any manual behaves this way. I placed my order a few weeks back though and should have my new baby in July.

 

Guys/gals, it's all RPM-dependent ... coasting in neutral has your car running at idle (more or less), using a limited amount of gas ... driving in gear nearly always has you running at some multiple of idle, hence using more gas. Common sense, really. And wearing of pads and/or rotors using the coasting scenario is marginal. You're not going to wear them at anywhere near double the normal wear rate, so it's a moot point.

 

Coasting in nuetral in a manual transmission does not harm the transmission, provided you have your foot off the clutch pedal (clutch engaged). If you are holding the clutch pedal down while you coast (clutch disengaged), you are lightly loading the throwout bearing, and ever-so-slowly wearing it out.

Many cars today shut off the fuel when you are coasting in gear. No car shuts off the fuel when you are coasting in neutral. I don't know what BMW/Mini's coasting fuel strategy is, so I can't comment on fuel economy differences, but it would be very slight indeed.

I agree that coasting in nuetral (with your foot off the clutch pedal) does nothing of harm to the vehicle.

 

Oops, double posted.

 

WELL, I'm not a mechanic, but a real Magnum P.I. Fan. MAGNUM once said it's best to downshift instead of brake, especially around tight turns. (Actually, it was one of the episodes where someone cut the brake lines in his Ferrari, so he pretty much had to.) ANYWAY...as dumb as it sounds, n every manual-transmission I've owned, I've practiced the whole down-shifting thing -- whether it be around tight turns or coming to stoplights, down ramps, etc. It really does help with the easing up on acceleration/decceleration thing that eats up gas (even if it's just a few cents worth here and there -- beggars can't be choosers!!) Besides...it means I have more power readily available to boost through those turns, making them SO much more fun!!! (The husband screaming and clutching the door handle kinda detracts, but hey...he's still in training.) End state is that I end up doing a lot more leg work, and may have to do more clutch replacement in the long run,... but I get a lot more power and a bunch better gas milage.

As for the battery / extraneous power-suckers: check out some of the threads on "things you didn't know about your Mini." Some of the much-smarter-than-me gear heads say that the Minis from 2004+ have been programmed to shut down the extras when you power down the car -- to save the battery FOR you. WHich is why things like the windshield wipers (front & back) may LOOK like they're on with the switches, but don't work unless you turn 'em off and back on again. If you have something plugged into the cigarette lighter, it won't be powered if the car is off for the same reason.

Hope it's a good steak, but i agree with Motor On -- treat the poor girl to dessert!! She's only out for the health of the Mini!!!!!

 

most new cars shut down fuel over about 2k rpm's without throttle input. Therefore, if you're going down a hill and can keep it in gear, over 2k rpms, you're saving on fuel. The engine is simply sucking air in and pushing it out, no gas being used at all. BUT if you have to get on the throttle even the slightest bit to overcome the bit that your engine is slowing your car down, you're wasting gas, so go to neutral.

 

Wouldn't leaving A/C, Radio, Lights on...etc when starting up draw more from your battery? I think this was the reason why some cars don't start on the first turn of the key??? Thus reducing the batteries charge over time prematurely. I deduce this from my lights diming when I leave them on on start up.

 

Well, technically, the Stop/Start enabled MINIs in the UK might shut the fuel off by completely turning the engine off.

Our drive home has one long hill in particular that slowly steepens and there's a noticeable difference when the ECU cuts off the injectors. The OBC jumps the current MPG from 60-70 to pegged at 99.9MPG, and the engine load increases enough to slow the car down.

It's a common enough feature that it happens with my 92 Probe, I'm told it works on the Probe by monitoring crankcase pressure for signs of deceleration.

for covering keeping the clutch out.

 

Can you explain this to me? I don't understand how the engine can still be running if there is no fuel being provided to the cylinders. No fuel = no combustion.

If the engine was just sucking air in without any fuel the motor wouldn't actually be running because there is nothing to burn, right?

I'm totally confused.

 

I guess I have the same question for you as the other post. I'm totally confused. If the throttle body closes entirely there is no air being fed to the engine. How can the cylinders even move if there is no air to relieve the vacuum within the cylinder?