I just read a couple threads here regarding coasting in neutral, but I wanted to find out exactly why it IS bad for your tranny when coasting in neutral at high speeds.

Thanks

 

who said its bad?

its dangerous in the sense that your tranny is disconnected from the engine at that point, so you won't have any throttle control if something happens

 

Its not bad for the car, but dangerous for your safety.

The only reason I found to really coast in neutral is to save some fuel. I sometimes "coast in neutral" in traffic situations which I'm traveling less than 15MPH. If I'm going like 80MPH and Coasting in Neutral, then that means I probably don't want to live anymore.

 

I'm in neutral on only one place, offramps.

 

I knew someone who was involved in a serious accident while coasting down a grade to save fuel in a suv. They were going 65-70mph and a deer ran out in front of them. The driver swerved to avoid hitting it and lost control and flipped several times. They did survive though. With a vehicle in neutral what ever you're driving will feel very loose and sloppy. Have you ever tried going around a semi tight turn in OD? The car will feel somewhat unstable but if you drop it down to 3rd (auto cars of course) it feels much more secure and tight.

Dave
02 Maxima SE

 

The car is already in momentum, placing the tranny in neutral is not going to save you much gas. I know the prices are up, but if you do this for about 10yrs, its possible you might just save youself 1 tank of gas. IMO that one tank (or whatever it is) is not worth the risk of having your car out of gear. You never know when you need it, better it be in gear and you be ready.

 

I coast in neutral all the time.

BTW coasting in neutral does not affect the steering!

 

Every owner's manual I've ever read discourages it because of the safety issue mentioned. I seem to remember reading somewhere that coasting is also bad because the transmission is not lubricated as well when everything is stationary except the input and output shafts(as when coasting in neutral). It's probably unlikely to cause damage for short periods during normal driving, but towing a manual tranny car in neutral with the drive wheels on the ground would be an example, no lube splashing around to keep the output shaft and its bearings lubed properly. BTW.... it's never a good idea to depress the clutch and rev the engine hard, the clutch release bearing and pilot bearing might survive it, but they do not take that high rpm abuse well, especially if they are getting a little dry with age. Remember, if the clutch is depressed, the release bearing will spin at the rpm of the engine and the pilot bearing will spin at an rpm equal to the difference of the engine and input shaft, which can still be pretty high.

 

I'll tell you one more advantage of coasting with the drive train fully engaged: cylinder vacuum.

On all engines controlled with a throttle butterfly, when you close the throttle shut and the engine is braking against the closed throttle, there is a slight vacuum created in the combustion chamber that pulls up a bit of oil mist from the crankcase up thru the oil ring and aids in lubricating the two compression rings.

That's exactly why the owner's manual (this one and all others I've read)suggests that during break-in you vary the engine speed...because coasting a bit against the tranny (engine braking) is actually GOOD for the engine.

BTW, this only holds true for engines that are throttled via a butterfly (or slide valve) that can open and shut, meaning basically all gas engines; diesels are not throttled via a butterfly but rather with the amount of fuel being injected. Which is why a diesel can 'run away' to a bazzilion RPMs and blow up if the governor fails....because there is no butterfly to close and shut off the flow of air into the engine....

 

Atleast he saved gas............

 

I'm not sure I agree with some of this. If the engine is on and you are in neutral and coasting, both the input and output shafts will be moving. The input shaft is connected directly to the clutch which will be engaged and thus turning. The output shaft is connected to the drive wheels and will also be turning. The only stationary parts are those that don't move regardless of whether or not you are in gear, like the selection fork, etc.
You do make a point, however, on improper lubrication if towing the car on the drive wheels. The reason this particular example is a problem is because only the output shaft will moving. The output shaft only connects to the gears when one is selected. I would believe that it is the gear movement that provides the most substantial fluid movement. When the engine is on, the input shaft and all gears, input and output shaft located, will be moving and providing lubrication. However, in the towing example, only the output shaft, no gears, will be moving and I suspect this does not provide adequate fluid movement due to the relatively smooth surface of the shaft.

 

Here is the real reason, as quoted from every owners manual I've read...

It is bad to coast in neutral, especially at high speeds, because in the event of emergency maneuver breaking, you have a much higher risk of brake failure. With the tranny engaged, the engine and tranny will both help you slow down by downshifting for you at the appropriate times, which helps you stop. With the tranny disengaged, all of the weight of the vehicle is put on your brakes completely, and they will heat up faster, and fail faster!

 

Do you think the reason it flipped is because it was a top heavy SUV.

 

Hi Adam! Long time no see man!

 

been coasting in neutral for years, my dad did it, and his dad did it.

its a family tradition, and no owner's manual is gonna change my mind

 

Hey Justin,
How've you been.

Work's been killing me lately. I hope the worst is over for a while.



Anyway I coast all the time. There are only a few instances I won't. Those mainly involve low visibility of any sort.

 

>Do you think the reason it flipped is because it was a top heavy SUV.

I am sure this did not help but the vehicle was a Honda Passport (Isuzu with Honda badges) and there are plenty more top heavy suv's out there. Btw he was actually issued a citation by the CHP for coasting in neutral. He should have not admited to it.

> coasting doesn't affect steering!

Maybe it doesn't affect steering directly but it WILL affect the way what ever you are driving handles at speed.

Dave
02 Maxima SE

 

Please people, the fact is coasting in neutral is NOT necessary.

Its OK to coast at a slow speed to a stop (40MPH~0MPH), because at this speed car is still very control able in neutral.

However, if you are doing anything above 50MPH and coasting in neutral WILL BE DANGEROUS!

For your safety just don't do it. Saving couple drops of gasoline doesn't worth your life.

 

Well said bro