Proper way to take hills (downhill) in manual... coast or engine brake? I'm confused.

[MrEcted]

I learned to drive a manual about 10 years ago when I was 17... I pretty much taught myself. I've always thrown the car into neutral when going downhill because it seems as though it does a lot less wear on your tranny/clutch, but more wear on your breaks (but much less expensive to repair). I've never been sure if this was correct or not, so I did a seach online and it seems as though there are two different camps on this topic.

First there are the people that do the same thing I do and think that engine braking causes a lot more wear then just braking while in neutral.

But there is the other camp that uses engine braking for a couple reasons. First it does less wear on your breaks but most importantly if you're in gear when going downhill then it's much easier to accelerate in the event of an emergency... but doesn't this cause major costly repairs down the road?

Now I don't know what I should do... which is why I'm asking you guys. Should I just keep doing what i've been doing, or is engine braking better?

[UncleBob]

the wear on tranny argument is pretty much false. Other than jamming gears, there's no notable wear worth mentioning.

Wear on the engine could be argued. I'd say a general rule is, its perfectly safe as long as you keep the RPM's realistic. Engine braking at redline isn't a good thing...all the time. But say, 1/2 redline or less, perfectly fine.

[curtis73]

agreed. Reasonable engine braking saves brakes without any damage at all to the engine or transmission. Big trucks do it with 80,000 lbs behind them. Its fine for your car.

I prefer using engine braking. Not only does it save my brakes, it keeps them from getting overheated. The chances of needing power to avoid an emergency are so slim, but needing good braking to avoid an emergency is very probable.

An added benefit to using engine braking instead of neutral is that modern EFI cars use no fuel while decellerating, but if you put it in neutral and let it idle, it does use fuel. If your foot is off the accelerator the computer only injects enough fuel to maintain idle. If its in gear and gravity is keeping the engine above idle, then no fuel is being injected. If you put it in neutral, its using fuel. This theory of course holds no water for carbureted engines which ingest fuel anyway.

[UncleBob]

Originally Posted by curtis73

This theory of course holds no water for carbureted engines which ingest fuel anyway.

feed back carbs would usually shut off fuel via a solenoid in the carb, but if its not a feed back carb, they usually go rich to prevent back firing in the exhaust

Not that we're talking enough fuel to really justify either situation IMO

[KiwiBacon]

My old EFI corolla shut of fuel at 1500rpm when coasting, you could feel the subtle difference in engine braking at that point. But the shopping cart I have now doesn't show up.
A workshop manual for it (different car, different country, same engine) lists 4000rpm as the cutoff point for coasting, the only reason I can see for such a high point is to keep the cat warm for emissions control.

Does anyone know if mechanically injected diesels can shut off fully or whether they inject the standard idle quantity? It's a question that's been in the back of my mind for a long time.

[bobss396]

I just leave it in high gear and brake accordingly. I will take it out of over drive if so equipped, you lose significant engine braking while in OD.

Bob

[72chevelleOhio]

Originally Posted by KiwiBacon

Does anyone know if mechanically injected diesels can shut off fully or whether they inject the standard idle quantity?

Mechanically will always inject fuel, its mechanical. Electronic will shut off the fuel.

[2.2 Straight six]

if it's a purely mechanical fuel system it'll always inject fuel.

common-rail diesels shut off.

[KiwiBacon]

Originally Posted by 72chevelleOhio

Mechanically will always inject fuel, its mechanical. Electronic will shut off the fuel.

The mechanical pumps do have the ability to completely shut off delivery. My question is, can the governor do this?

[72chevelleOhio]

Originally Posted by KiwiBacon

The mechanical pumps do have the ability to completely shut off delivery. My question is, can the governor do this?

Not to say its true for all diesel engines, but the mechanical pumps shut off fuel only to shut the engine down. depending on the engine, the governor will maintain idle and no load (max rpm) not shut the fuel off. Thats why the old big rigs smoked badly. They couldn't shut off the fuel while using the engine (jake) brake.

[KiwiBacon]

Originally Posted by 72chevelleOhio

Not to say its true for all diesel engines, but the mechanical pumps shut off fuel only to shut the engine down. depending on the engine, the governor will maintain idle and no load (max rpm) not shut the fuel off. Thats why the old big rigs smoked badly. They couldn't shut off the fuel while using the engine (jake) brake.

On inline pumps like on my truck, the max fuel is indeed limited, max rpm and idle rpm are too. But the rpm's are limited by the governor, which has the ability reduce fuelling below what is required at idle.

[72chevelleOhio]

Originally Posted by KiwiBacon

On inline pumps like on my truck, the max fuel is indeed limited, max rpm and idle rpm are too. But the rpm's are limited by the governor, which has the ability reduce fuelling below what is required at idle.

I would think it would still flow fuel for cooling and lubrication of the mechanical injection pump, on electronic systems the fuel is still pushed thru the injecters (or electronic unit pumps on other engines) for cooling and lube but is not injected.

[KiwiBacon]

Originally Posted by 72chevelleOhio

I would think it would still flow fuel for cooling and lubrication of the mechanical injection pump, on electronic systems the fuel is still pushed thru the injecters (or electronic unit pumps on other engines) for cooling and lube but is not injected.

The mechanical pumps process fuel for cooling all the time, it has very little to do with the volume going to the injectors.
The inline pumps are oil lubricated.

[72chevelleOhio]

Originally Posted by KiwiBacon

The mechanical pumps process fuel for cooling all the time, it has very little to do with the volume going to the injectors.
The inline pumps are oil lubricated.

Process? you mean flow or move? the pump isn't filtering, seperating or changing the state of the fuel.
Very little? if its a mechanical pump its going to the injecters.
Oil lubed on one side, lubed by the fuel on the other, some are totally lubed by fuel only. (the newest Detroit Diesel engine-DD15)

[KiwiBacon]

Originally Posted by 72chevelleOhio

Process? you mean flow or move? the pump isn't filtering, seperating or changing the state of the fuel.
Very little? if its a mechanical pump its going to the injecters.
Oil lubed on one side, lubed by the fuel on the other, some are totally lubed by fuel only. (the newest Detroit Diesel engine-DD15)

Process meaning take from the feed line, cycle through the pump and return to the tank.
Yes it filters that, no idea what mean by "seperating or changing the state of the fuel". Sounds like you're trying to sell a snake oil fuel catalyst.

Oil lubed through the housing, governor, bearings and cam. Yes I know many are only fuel lubed, but the Bosch type A isn't one of them.