Coasting downhill in my car in neutral: how bad?

[handy]

"One thing I did not see mentioned about shutting off the engine when coasting is the loss of power steering. "

Yeah, but you can still steer.

[Freiheit]

What about manual trannies?

I live on a hill, and my dad criticizes me for going down it in neutral every day.

[Skillet38]

I have a manual transmision in my Toyota Tundra. I often pop it into neutral going downhill. NO i’m not going to burn up my brakes, I know how to use a clutch and usually only do it when there’s a hill ahead to provide natural braking.

I also downshift to assist in braking on occasion ( I know some people equate this with stomping on kittens ).

The only real concern I have is the sudden change in oil pressure. I’d like some insight into this from any gear heads out there, as to potential stress to the motor.

** Country Squire ** funny how in your OP you never mentioned turning the motor off lol yet it became a big topic.

[Rick]

*Originally posted by something clever *
**wow, there is so much incorrect information in this thread. but i guess that is normal when it comes to cars. everyone thinks they’re an expert. ill sum all the points up in one post, i saw a few posts with good information but they are surrounded by wives tales and just plain ignorance. **

Quite true

Modern cars have lockup torque converters… when youre going down the highway at 70mph and let off the gas, the rpms will NOT drop to idle. When a torque converter locks up, the car is essentially like a manual transmission, there is no slippage, it is a direct mechanical link. This usually happens above 45mph as long as overdrive is turned on, and you are not at wide open throttle.

Well I can’t say for sure on all lockup converter auto transmissions, but on the ones I teach on the converter unlocks whenever the brake is applied or the throttle is returned to idle.

**

With that said, no, it wont hurt. coast down a hill, big whoop dee doo. Some of you are partially right. Towing an automatic RWD car with the rear wheels on the ground is a bad idea if youre going long distances. If that is the case you need to remove the driveshaft.**

In some cases a long distance can be defined as just a couple of miles (yes I have seen transmissions get killed by a tow truck driver not dollying or flat bedding a 5 mile tow.)

**

But since we’re not talking about towing… as long as the engine is on, the front pump in the tranny will be getting fluid. AND SINCE WE ARE IN NEUTRAL AT THIS POINT, there is no need for a high line pressure, because the transmission is in neutral. **

I agree with this statement.

**

having the engine go from idle (probably5-800rpm) to say 2,000 or so is fine for the engine but it could eventually cause problems for the transmission, since you dont have a performance car or anything, you would most likely NEVER NOTICE. if you want to be safe and you have a tach, get the rpms back up to ~2000 or so before putting it back in gear. its similar to what you would do if you had a manual tranny… 80mph on the freeway, you pop it in neutral going downhill… you wouldnt justput it back in to gear and pop the clutch, youd try to match the engine rpm with where it should be. same principle. **

I have coasted down hills in N before. when it was time to re-engage the trans, there is a shock to the system as the clutches and brakes inside the unit apply. While this shock may not necessarily shorten the life of the trans, for sure it, won’t be increasing it.

On the transmissions that I am familar with and teach on, when in drive and the throttle is closed the troque converter will unlock, and if on flat ground the engine will return to idle (or very close to it) If decending a hill the speed of the car will be increasing (gravity) and the rpm will hang at above idle. This is not really engine braking, as it will not occur on flat ground. I have never really given much thought as to why it does this. If somebody REALLY wants to know I suppose I could pull out some hydraulic system charts and apply diagrams and figure it out. In any case, if the driver downshifts one gear, then the transmission is set up in such a way that engine braking is present. Feel free to try slowing down in your own car in D and then repeat in the next lower gear.

While I am on the subject Osip Most cars nowadays (and I will say most, becasue there could be an exception somewhere) the engine management computer turns off the injectors on decell. This means that if you take your foot off the gas the injectors shut off. This is done for both fuel mileage and emissions (hey no injection, no emissions) so by putting your car in neutral you are probably increasing the amount of fuel used.
:smack:
My car has a trip computer. When driving in the hills if you look at the instanious fuel mileage you will see it peg at 99.9 MPG when you go down a hill, as no fuel is being injected.

[Skillet38]

*Originally posted by Rick *
…
While I am on the subject Osip Most cars nowadays (and I will say most, becasue there could be an exception somewhere) the engine management computer turns off the injectors on decell. This means that if you take your foot off the gas the injectors shut off. This is done for both fuel mileage and emissions (hey no injection, no emissions) so by putting your car in neutral you are probably increasing the amount of fuel used.
:smack:
My car has a trip computer. When driving in the hills if you look at the instanious fuel mileage you will see it peg at 99.9 MPG when you go down a hill, as no fuel is being injected. **

interesting observations. the point I want to make (in my manual tranny), is that I go Faster downhill coasting than if I take my foot off the gas. In fact the instances when I’m tempted to do so are such that I actually accelerate with either the clutch in or the tranny in N . . . . .

[Rick]

*Originally posted by Skillet38 *
**interesting observations. the point I want to make (in my manual tranny), is that I go Faster downhill coasting than if I take my foot off the gas. In fact the instances when I’m tempted to do so are such that I actually accelerate with either the clutch in or the tranny in N . . . . . **

Manual trannys are a different kettle of fish than a automatic. In a manual there is a direct connection between the engine and the rear wheels at all times when the car is A) In gear and B) the clutch is engaged (No foot on clutch pedal)
So when you take your foot off the gas in manual the engine works to brake the drive wheels, this does not happen in an automatic in Drive. (usually)
So yes pushing in the clutch or shifting into N you will pick up speed on a down hill.

[GusNSpot]

*Originally posted by x-ray vision *
**Get a clue Gus. **

It was a joke? It was a joke? It was a joke?
Argahhhhhhhhh :smack: :eek: ;j :wally

Where is the clue store?
.