I had to drive long downhills and used the "engine break" to keep the speed from increasing. I was a bit worried I may cause damage to the engine, because I was afraid that at long decelerations the motor would not get enough oil for lubing it properly. (To some extent the situation is similar to a 2stroke engine - no fuel injection no motor lubrication.)

There was a therad on "Engine braking", but it did not help to answer my question this lubing issue was not mentioned.

 

adding question to the question above :
i have similar situation and sometimes i just put the gear in neutral and let the car
glide down the hill until a stop sign.
is it okay to do that

 

Man, *nothing* compares to the smug feeling you get, gliding downhill in neutral, thinking about all the gas your saving. It'll take a lot to convince me to stop doing that.

 

Gliding downhill in neutral can be bad for the tranny, depending on the design. As long a fluid is flowing based on movement from the driveshaft, it is fine. Does anyone know if the 8's tranny still has fluid flow in neutral?

 

Engine braking supposedly is not good for the life of the engine/gas mileage. While it won't considerably cut down the engine life. But will inevitably speed up the wear and tear on the engine. But this is from experience of driving a piston engine. I for one have no experience driving rotory power car(you haven't lived until you get to drive a wankel). Also letting your car idle for long periods of time and suddenly jumping on the RPM is bad. Engines were meant to be kept running constantly at the same speed. But hey I also use engine braking all the time and cruise on neutral as much as possible. :p

 

It is not bad to coast down hill in gear. The gas is cut off to the engine and you will inprove your MPG! If you dont have it in a gear then it is useing gas. This is how the 8 is programed.

 

its bad to coast in neutral... well, dangerous. if you need to make fast adjustments, being in neutral is a bad idea.

 

That, and doesn't the ecu go into idle fueling mode in neutral(more fuel?) vice decelleration mode when engine braking (no fuel?)

 

I'm sure the engineers have taken this into account. Going down hills is part of driving. Also, I imagine the oil pumps are driven by the engine, so if the engine is spinning, the pumps are pumping.

Regarding 2-stroke engines, the first 2-stroke motorcycle I ever owned (1970 Yamaha 175cc Enduro) had automatic oil injection. The oil injection did not shut off when coasting. Throttle position and RPM played a factor in how much oil was injected.

1.3L

 

^^^ What Old Rotor said. When you are coasting in gear, the ecu goes into Deceleration Fuel Cutoff (DFCO) mode, and actually stops injecting fuel. the motion of the car turns the wheels, which turns the tranny, which turns the engine. no fuel needed to keep the engine running.

if you are in neutral, then the motion of the car turns the wheels, whichs turns the tranny, but not the engine because you are in neutral. so to keep the engine turning, fuel has to be injected into the engine.

 

^^^ What Glyphon said.

Another thing to consider ... one of the tricks to driving safely is having the option to able to accelerate out of a dangerous situation. Say you're going down a hill and you have a truck behind you which loses its brakes and starts accelerating towards you. You have no shoulder and there is oncoming traffic... only way out is to go faster.

Scenario 1: You're rolling down in neutral... you plant your foot. The engine revs you go nowhere. You go to get back in gear... whack... too late.

Scenario 2: You're in gear... you plant the foot... off you go.

I know it's unlikely... but you never know.

 

thats what i meant, just the more graphical explanation hits home better

 

Sorry.. re-reading your post.. yep we're on the same page. You know what they say about great minds :D

 

It is illegal to coast in neutral in CA.

 

just a curiousity, how would they catch that? (if they even bother)

 

Born.. to be wiiiiiiild!!!....

Krankor
05 Shinka 6MT

(actually, I don't actually pull it out of gear, I just clutch it neutral, from which I can get back quickly enough)

 

That's gonna put excess wear on your throwout bearing...

There's no detriment to going down a hill in gear with your foot completely off the gas. It's less gas use than idling (there is *no* fuel injected when coasting down a hill in-gear, which can be verified by observing the wbo2 sensor readings) and as far as lubrication goes, the oil is injected into the rotor housings via different means than the fuel injectors, so the housings are still getting lubed.

In neutral you've got the driveshaft spinning fast whereas the idling of the engine may not be spinning the front side fast enough for proper oilflow in the gearbox (that's speculation on my part). If you push the clutch in there's that and the added wear on your throwout bearing.

 

You guys are full of it. Coasting in neutral does not damage the transmission. In neutral with the clutch out, the layshaft is spinning at the same speed as the engine (idle) so it is indeed spinning and getting lubricated. Same for the driveshaft assembly, which is always turning at rear-wheel speed anyway.

Now you CAN damage your transmission by towing the car with the rear wheels on the ground and the trans. in neutral. The solution is to start the engine up every 100 mi or so and let it spin the layshaft (clutch out, in neutral) for a bit to get it lubricated. A better solution is to just disconnect the driveshaft.

Finally, its always better to use the piece of your car that's replaceable, ie. the brakes to slow the car, rather than the engine. Its highly unlikely that your brakes will overheat even on the steepest of slopes, so there's no real need for engine braking.

 

you speak like a man who has never had his brakes go out at highway speed. The brakes themselves might not over heat, but it is possible for the brake fluid to boil. and when that happens, you essentially have no brakes. besides, engine braking going down a hill is more about controlling your speed as opposed to actually braking.

 

That happened to you on your RX-8? These cars have the best brakes Mazda has ever done.

 

I do know that most autos dont engine brake, and living in colorado there are alot of passes that are 40+ miles from top to bottom. So riding your breaks for most of 40 miles will cause any breaks to over heat and fail. I have seen hundreds of smoking breaks in the mountains. I have owned several rotaries and engine braking has never had any detrimental effect that I have ever seen.

 

I'm not totally against engine braking, I'm just suggesting that most of the time, its not necessary. I know some people who do it going up to stoplights on level ground thinking they are saving their brakes, which doesn't make much sense when you consider a set of pads is < $150. In any case, you won't damage the engine because fuel and oil are always being injected into the engine, even if you are totally off the throttle.

 

This is incorrect. Any type brake system can overheat if you drag them long enough and far enough. I've sat at the base of some long, steep grades and smelled the blistering hot brakes of some pretty fancy cars when the drivers dragged the brakes all the way down the hill. Hot brakes can boil the fluid and then complete brake failure happens. Selecting a lower gear is the solution, not dragging the brakes. Sure, it's cheaper to replace worn brake pads, but that doesn't take into account the consequences of brake failure (i.e., crashing your car) .

1.3L

 

nope. not on my rx-8. different car. but that doesn't mean if you ride your brakes down an extended slope that they won't fail from over heating.

i agree, that for stopping the car the brakes are the best way to go. but for controlling speed on a hill or shifting to stay in the powerband while coasting to a stop, there's nothing wrong with such behavior and it isn't detrimental to the car.

 

Never coast in neutral, engine braking is actually not as detrimental as you might think. It only uses your engine compression to slow down, in fact it was purposely implemented in big trucks to assist the brakes for slowing down; u know... the psssstttt sound when a bus or truck makes before stopping. In fact engine braking is one of the most important factor of proper engine break-in, I don't know if its any different in a rotary engine but in a piston engine the compression actually forces the piston ring to properly seat. Loading the engine is actually good for the engine during break-in period provided the engine is warmed up properly and it doesn't overheat if run at high rpm over long period. Furthermore the car's manual mentioned not to keep speed constant for long time is to prevent the piston ring and cylinder from glazing. Engine surface are peaks and valleys, what u try to achieve during break-in is making the peaks into plateaus so a little bit of oil still manage to lube the walls during operation. More importantly "in gear" is safer