Free-wheeling

free-wheeling: Less fuel than accelerating but more than no acceleration in gear (provided it's an injection car). A little more wear on the brakes, a lot less wear on other components like the cam belt and gear box. Running in-gear on the other hand can provide significant wear on the engine components, especially when braking as well.
 
UnUnOctium said:
free-wheeling: Less fuel than accelerating but more than no acceleration in gear (provided it's an injection car). A little more wear on the brakes, a lot less wear on other components like the cam belt and gear box. Running in-gear on the other hand can provide significant wear on the engine components, especially when braking as well.
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wtf?! How do you figure this?
 
Sinbad said:
wtf?! How do you figure this?
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It's very similar to that song about how all the bones are connected.

Simply: running gear connected to gearbox which is connected to engine. In-gear you have a link with no slack. Simply put, you can force the engine to reduce revolutions (i.e. braking in-gear) rather than let it reduce on its own (neutral, no accelerator). This means that you're providing a moment opposite to that which the engine is generating through its natural rotation. Since the crank shaft is connected directly to the cam belt (and a whole assortment of other belts) and the gearbox applies this force on the crank shaft, you have a situation where you're effectively pulling it the other way due to the rotational inertia already present in the cam shaft, crank shaft, etc.

In simpler terms, it's equivalent to stopping a free-wheeling tyre of an upside-down bicycle with your hands rather than letting it slow to a stop due to resistance.
 
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UnUnOctium said:
It's very similar to that song about how all the bones are connected.

Simply: running gear connected to gearbox which is connected to engine. In-gear you have a link with no slack. Simply put, you can force the engine to reduce revolutions (i.e. braking in-gear) rather than let it reduce on its own (neutral, no accelerator). This means that you're providing a moment opposite to that which the engine is generating through its natural rotation. Since the crank shaft is connected directly to the cam belt (and a whole assortment of other belts) and the gearbox applies this force on the crank shaft, you have a situation where you're effectively pulling it the other way due to the rotational inertia already present in the cam shaft, crank shaft, etc.

In simpler terms, it's equivalent to stopping a free-wheeling tyre of an upside-down bicycle with your hands rather than letting it slow to a stop due to resistance.
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No it's not... your engine is designed to turn. Turning it isn't going to increase its wear and tear at all.
 
Sinbad said:
No it's not... your engine is designed to turn. Turning it isn't going to increase its wear and tear at all.
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Engine, yes. Always turns the same way.

Drive train though is designed for forward (accelerating) motion, not for backwards (slowing). Drive train stressing the other way is apparently not good.

I do it, in 5th down most hills. If revs get down towards 1k, I'll drop to 4th.
 
Budza said:
Engine, yes. Always turns the same way.

Drive train though is designed for forward (accelerating) motion, not for backwards (slowing). Drive train stressing the other way is apparently not good.

I do it, in 5th down most hills. If revs get down towards 1k, I'll drop to 4th.
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Erm... I'd hazard that drivetrains are quite sufficiently engineered for both as, well, that's how one drives. :p
 
Sinbad said:
No it's not... your engine is designed to turn. Turning it isn't going to increase its wear and tear at all.
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I'm not saying turning is bad, I'm saying applying two moments in different directions is. What it most often translates to is a looser than average cam belt over time (which is a bad thing) but also reflects in some wear and tear on the gearbox. It's similar to trying to hold the cam belt while the engine is running, not a good thing, no?

Free-wheeling is illegal simply because it's dangerous in the rain if you don't know your car's limits.
 
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UnUnOctium said:
I'm not saying turning is bad, I'm saying applying two moments in different directions is. What it most often translates to is a looser than average cam belt over time (which is a bad thing) but also reflects in some wear and tear on the gearbox. It's similar to trying to hold the cam belt while the engine is running, not a good thing, no?

Free-wheeling is illegal simply because it's dangerous in the rain if you don't know your car's limits.
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I'm sorry, but you're way off the mark here.

The cambelt is ALWAYS driven ONE WAY ONLY. Accelerating/freewheeling will not change the direction or force on the cambelt to any significant degree - and it certainly won't cause a reversal of the forces on the belt.
Also, cambelt stretching is countered by the cambelt tensioner - so is a non-issue. It's nothing at all like trying to hold the cambelt.

Gearbox - the gears are machined from metal - not some magical substance that's weaker in one direction than another..
 
Common sense. Anyone with a trip computer knows, for the best fuel consumption, keep it in gear when "freewheeling". As explained, the wheels and not combustion, will keep the engine turning. When freewheeling in neutral, the wheels are not connected to the engine, so the engine has to use fuel to keep turning.

There is absolutely no reason why you should not to keep the engine in 4th/5th gear down a hill and take your foot of the accelerator.
 
Voicy said:
The 2-stroke comment was made because 2-stroke engines use a mixture of petrol and oil as lubrication. If you are in neutral, the engine doesn't get lubricated and you develop issues.
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Actually, when you're free-wheeling in neutral, your engine is idling, and getting just as much lubrication as it would be when idling at standstill. When you are running down a hill under compression with the throttle closed, you are getting far less fuel (and oil) into the engine at higher revs, and that when the engine runs the risk of being under-lubricated.
 
Firstly from what I can gather, the OP is not talking about engine braking (in other words, slowing down using the engine, car still in gear) - they're referring to maintaining speed/ picking up speed. So remaining in gear should be fine.

Moderate engine braking is ok, you're not placing undue strain on your engine parts.
If you're doing say 100 though, and put your car in 2nd to slow down instead of using your brakes, yeah, I don't think that's wise.
 
Budza said:
The directional stress on the moving parts reverses, yes. Drive-shaft is now effectively being used to brake the car, not accelerate it.
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I think I understand what you are saying. They're not turning in a different direction, but now the force comes from the wheels back to the engine via the drivetrain. Which is not bad for the engine. It does actually save more fuel than free-wheeling out of gear, but I don't believe this will be a noticeable amount.
 
Slootvreter said:
I think I understand what you are saying. They're not turning in a different direction, but now the force comes from the wheels back to the engine via the drivetrain. Which is not bad for the engine. It does actually save more fuel than free-wheeling out of gear, but I don't believe this will be a noticeable amount.
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Yep. My mechanic reckons the stress of engine braking isn't worth it. Either way, I tend to stay in gear.
 
Budza said:
Yep. My mechanic reckons the stress of engine braking isn't worth it. Either way, I tend to stay in gear.
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How else should people drive normally anyways?You either leave it in a gear suitable for the speed (advisable), or engage neutral (not advisable). Correct?
 
Coasting is illegal for various reasons as already explained by some of you. That's it.

Just leave it in gear when decelerating or going downhill. All cars are designed to do that, so will have no negative impact at all.

Some electric cars actually charge the batteries when decelerating.
 
Colin62 said:
When you are running down a hill under compression with the throttle closed, you are getting far less fuel (and oil) into the engine at higher revs, and that when the engine runs the risk of being under-lubricated.
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Not on any car engine I know of. Oil pump is turned by the crank shaft. The lubrication is dependant on RPM, not throttle position or amount of fuel in the engine.

Budza said:
Yep. My mechanic reckons the stress of engine braking isn't worth it.
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Highly doubtful, no fuel is injected and therefore the cylinder is only heating by air being constantly compressed (actually losing more heat than it is generating). The transmission on most engines deal with much, much worse than a little down-hill action. For example going up a hill. If you go up a hill at low RPMs and/or full open throttle (foot down, or close to completely down) that is the maximum load you can place on an engine and transmission. Especially at low RPM (the engine gets incredible hot and the crank and every transmission component is under massive load) It is in fact so much load that many turbo charged cars cannot tow for exactly that reason. The manufacturers fear that the drivers (whom know nothing of engines) might try full throttle up a hill with a f#$#ing caravan, at which point the turbo engine explodes (literally, piston out the block).

Little know fact but if you drive from Johannesburg to Cape Town your engine experiences more wear in the first 5 minutes after turning the key than the entire rest of the journey. Basically because the engine and oil is not yet at operating temperature (90 degrees Celsius). Taking that into account your realize how trivial this wear of a downhill is in comparison. If it is even higher (which again I doubt).

That little piece of knowledge you'll find all over the web btw. and formed part of an oil add that aired on radio a few years ago (as to the reason you should buy better cold weather oil).

More info: http://www.thehcf.org/antiidlingprimer.html
 
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Gnome said:
Not on any car engine I know of. Oil pump is turned by the crank shaft. The lubrication is dependant on RPM, not throttle position or amount of fuel in the engine.
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Poster was referring to a 2 stroke...
 
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