Ok, let me say this, I consider myself slightly mechanically inclined. I'm proud to say I know how a transmission and engine work, and so on... One thing I don't know, and would like to know is, what would happen if your driving down the road (in a standard car lets say) and the motor shuts off, or you turn it off with the key. Would the car come to a screeching stop, because the motor has stopped? I know that the car won't just roll on down the road but will it come to a sudden stop, possibly causing an accident on the highway, or will the power of the wheels continue to keep the motor spinning, without oil being pumped through it causing internal damage?

Am I just thinking to much on a very simple subject here or is there a simple answer as to what happens?

Cheers

 

Same thing if you ran out of gas... the motor would shut off but you would roll to a stop.

 

Yeah, but the motor is still "connected" to the transmission, does it roll as if the car was in neutral?

 

I accidently switched my keys off with my knees while driving once. Had to roll to a stop, throw it in park, turn it back on, and drive again.

 

It rolls like its in gear(ala pop starting) it will continue to go down the road, though not free wheel as much as if it were in nuetral. I've had this happen to me a number of times on test drives over the years, certain older hondas are known for bad ignitions and you are driving and the car just shuts off and you slowly come to a stop. Typically all you have to do with those hondas is hold the key between the on position and the crank position and you can continue driving, but you must hold it there or the vehicle shuts off again. NEVER turn the iginition off while moving because it will lock the steering wheel and can be difficult to get back to on in order to turn, also power brakes are lost - but if you've driven a vehicle with out power brakes its not a big deal, just a little different then with power.

I did some testing with the G and the start/stop button is inactive while the vehicle is moving, however you can shut it off in gear if the vehicle is stopped.

 

A lot depends on the gear you are in. If you are in say fifth or sixth gear and the motor shuts down at moderate speeds, the car would basically slow down at a quicker rate than if you depressed the clutch. If you were in a lower gear then I imagine some bucking and jerking would be more prevalent as you coasted to a stop. This is basically controllable if you are not driving a rear wheel driven vehicle in slippery conditions. A pickup truck for example, may be difficult to control if driven in snow if locked into gear as it would begin to move from side to side.

In an automatic transmission equipped vehicle then basically nothing. Keep in mind the transmission is being driven through the torque converter via a fluid coupling. This is why some "slipping" occurs in older automatic equipped vehicles. No direct coupling is present. Now many new automatics have something called a torque converter clutch. These engage at a certain speed and allows the engine to have a direct coupling to the automatic transmission. This is basially for fuel economy. If this clutch fails and the engine shuts off, I would imagine it would behave much the same as an vehicle equipped with a manual transmission with the clutch engaged.

Terry

 

funny you should ask, i was wondering the same thing so as i was driving i shut my car off. To my surprise it didnt turn back on! so after panicking for a sec i realized the car wouldnt start in drive, so i popped it into neutral, turned the key and went on my way...

 

I briefly owned a Saab 9-5 and the ignition was located on the center console between the driver and passenger seat, I can't count how many times in the 4 months I had the car that either my passenger would bump the key, I would bump the key or I would have something bump the key into the off position while driving. You could roll to a stop if you wanted to as mentioned above but I became pretty skilled at popping the car into neutral and restarting in moments if necessary. It was pretty scary the first time it happened though, no power steering or brakes.

 

I'm not sure the original question was answered yet... he was asking if there would be any damage caused to the engine? Because if you're in gear/drive and the car suddenly stops, the transmission is still connected to the engine, yet the engine is still turning over but the oil circulating mechanisms have shut down. I'm pretty sure all of us have that knowledge already.

What the OP is asking is would there be any damage to the engine? I don't know for sure, but I'm similarly mechanically inclined, and I'm guessing the engine still turns over, but not enough to damage any components as there is still some oil present.

 

I doubt it. As mentioned, if the engine shuts off in an automatic equipped automobile the engine is not turning while the car is in gear (provided the torque converter clutch is working correctly). You would have more issues in regards to the transmission not being properly lubricated. In a manual equipped car the engine will still turn if the clutch is still engaged, and someone will may need to correct me in a few of the newer engines, but an oil pump is generally mechanical driven. If the engine turns the oil is still going through the engine, the pump still being driven via the reciprocating mass whether the engine is running or not.



Terry

 

Good info everybody :thumbsup;

Thanks.

 

That happened to me on the highway once courtesy of my drunk passenger. I got the keys back, put it in N, started the car again, put it back in D and kept on trucking.

 

I do this all the time when I'm coasting to a stop.

 

In gear?

 

No.

I shift to neutral, and shut the engine off. Then when the light turns green, off I go!

 

You could have put it in neutral whiile you were rolling, started it and put it in drive again