Sorry to stir the pot, but i want to hear what y'all think. I have noticed coming down 2 particular hills to and from work my 05 pathfinder shifts down and really ramps up the RPM when it does this. I have started to slip it in to Neutral at the top of the hill and coast down using the brakes to slow it down.
Why? You might ask, to ease strain on the engine, brakes are SO CHEAP why not wear down parts that are cheap and easy to replace.
I have read tons of stuff online about this. Anything from "don't do it, its more efficient to let the engine do it because the injectors shut off fuel," that's really hard for me to believe.
Another I read said its hard on U-joints and the differential because it slams them around, this i can at least fathom. But, what is the difference between parking on a hill and hearing your transmission jolt as you shift in reverse? I know every car does this due to the strain placed on the transmission to hold the car from rolling, the energy has to be released somewhere.
SO im interested to hear what you guys and gals who drive the same vehicle as me think about this?
Is coasting good to save fuel? Is it bad for you vehicle? Is it unsafe?
FIRE AWAY....
Coasting Opinions?
Moderator: volvite
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jetwrangler
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volvite
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Bad idea. Constant use of your brakes will end up causing your brakes to fail. Basically they will fade and you won't have the stopping power you need in the event of emergencies. That's why vehicles down shift etc going down hill to use the engine to slow down the vehicle and then use brakes. I know the following website is not the gospel truth, but instead of me writing it all out here is a link to read up more on brake fade. Don't do it.
http://en.wikipedia.org/wiki/Brake_fade
http://en.wikipedia.org/wiki/Brake_fade
Really bad idea. I have first hand experience with the Pathfinder brakes, and I can easily say that it does not take very much to make them fade & become dangerous. Rolling down a hill in neutral is just f'ing insane. The transmission can handle downhills just fine.volvite wrote:Bad idea. Don't do it.
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jetwrangler
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Ok I can see your point on Brake Fade. But really, its maybe a 150ft hill stretched out in 1/4 mile. It just more less annoys me to feel the truck downshift because i use the brake to start slowing down for a stoplight at the end of the 1/4 mile.
There is nothing "high performance or steep" about this hill. I have more faith in my brakes than that, if not i would not continue to drive the vehicle. The brakes are on there for a reason, the engine isn't meant to stop the vehicle.
But ill use it in a different light and see what ya think of it. Automatics obviously downshift by themselves, the pathfinders are relatively torque(y) and when they downshift they bump up the rpm, regardless of how you are slowing down. So if i am going up hill slowing down naturally from gravity and I put it in neutral to let the vehicle coast as I come to a stop light at the top of the off ramp is that bad. Obviously I pose this in a safe manner, ie: im not speeding, traffic if any is light.
Kinda funny to me, we went straight to brakes and I was thinking it would be bad for the transmission.
Thanks and keep the responses coming always interesting to see other viewpoints.
There is nothing "high performance or steep" about this hill. I have more faith in my brakes than that, if not i would not continue to drive the vehicle. The brakes are on there for a reason, the engine isn't meant to stop the vehicle.
But ill use it in a different light and see what ya think of it. Automatics obviously downshift by themselves, the pathfinders are relatively torque(y) and when they downshift they bump up the rpm, regardless of how you are slowing down. So if i am going up hill slowing down naturally from gravity and I put it in neutral to let the vehicle coast as I come to a stop light at the top of the off ramp is that bad. Obviously I pose this in a safe manner, ie: im not speeding, traffic if any is light.
Kinda funny to me, we went straight to brakes and I was thinking it would be bad for the transmission.
Thanks and keep the responses coming always interesting to see other viewpoints.
What kind of speeds are you talking about? I originally thought you were talking highway or freeway speeds, which makes me think of the "hill" I frequently drive between Salt Lake and Park City. There's a good 10 mile stretch of interstate that is just killer on brakes, so I'm usually driving down with the overdrive disabled & only touch the brakes a few times to slow down a bit. If you feel the transmission downshift because you are slowing down, then it is doing the intended job. Why not just manually pop it into a lower gear? What annoys me constantly is not having a manual transmission.jetwrangler wrote:Ok I can see your point on Brake Fade. But really, its maybe a 150ft hill stretched out in 1/4 mile. It just more less annoys me to feel the truck downshift because i use the brake to start slowing down for a stoplight at the end of the 1/4 mile.
It's been a while since I've looked through the owner's manual, but I'm pretty sure it talks about using the transmission to help slow the vehicle on hills. Can't say that I know if shifting into neutral while driving is good or bad since I know of nobody who does that, at least with an automatic transmission. I know it used to be a bad thing (high school autoshop, mechanic friends-all from eons ago).
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jetwrangler
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Yea after my last post I realized I should incorporate a speed into this equation. So on the down hill topping the hill at 40. On the up hill exiting interstate 60 and decreasing. So once again nothing extreme.
You are correct on the once upon a time, I was told the same thing in shop class, but we were talking Turbo 350's and the what have you. Things that don't require electricity
Yes I would do anything for a 5 speed stick.
And this might help explain my logic. When I drove/drive stick shifts I do not put it in gear until I need it. I coast unless i need to slow down or speed up. So you know what I do to accelerate, there's sorta only one way unless your grinding. But say i'm going down hill in a stick, I put the clutch in and keep it there until I needed power again. I might have the correct gear selected but always the clutch on the ground. Then I can use the clutch(engine braking, if really needed) and brake at my leisure to slow the car down.
Once again just asking for perspective, my biggest concern is it bad for the transmission?
You are correct on the once upon a time, I was told the same thing in shop class, but we were talking Turbo 350's and the what have you. Things that don't require electricity
Yes I would do anything for a 5 speed stick.
And this might help explain my logic. When I drove/drive stick shifts I do not put it in gear until I need it. I coast unless i need to slow down or speed up. So you know what I do to accelerate, there's sorta only one way unless your grinding. But say i'm going down hill in a stick, I put the clutch in and keep it there until I needed power again. I might have the correct gear selected but always the clutch on the ground. Then I can use the clutch(engine braking, if really needed) and brake at my leisure to slow the car down.
Once again just asking for perspective, my biggest concern is it bad for the transmission?
Actually in my wife's car, she has a stick and I sometimes downshift to slow the car rather than tapping the brakes. I was taught that this was OK and isn't hard on the engine plus it will save the brakes. As far as riding the brakes down a hill that's not good which is why your Pathfinder is downshifting. It's slowing you down by doing the same as someone who had a stick.
_________________
Michael
'08 Pathfinder LE V8
Looking at Indianapolis used cars.
_________________
Michael
'08 Pathfinder LE V8
Looking at Indianapolis used cars.
Last edited by MichaelT on Mon Nov 07, 2011 8:54 am, edited 1 time in total.
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jetwrangler
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"Actually in my wife's car, she has a stick and I sometimes downshift to slow the car rather than tapping the brakes. I was taught that this was OK and isn't hard on the engine plus it will save the brakes."
My logic is way different from yours. Brakes are cheap and inexpensive. I would much rather use them and wear them out than put any bit of extra strain on an engine. Putting more strain on an engine and potentially wearing something out prematurely is an expensive fix. Not to mention time consuming and also takes your vehicle away for days to weeks.
"As far as riding the brakes down a hill that's not good which is why your Pathfinder is downshifting. It's slowing you down by doing the same as someone who had a stick."
As for going down hill I am coasting, not riding the brakes. This is a short open stretch in which case i'm only using the brakes at the end of it. If i was riding the brakes while coasting I would not have it in gear to downshift in the first place.
I think I solved my own question by recording a little bit of data. This all started with the notion of keeping my rpm as low as possible, therefore saving gas. After a weeks time of shifting into N for coasting purposes and then leaving it in D for a week on the same hills. I have come to the conclusion that the RPM only varies by a minuscule amount. Either way the truck will stay around 1000 RPM or just above. The only time the RPM isn't around 1000 is on the initial downshift.
Thanks for the opinions and ideas.
"knowing is half the battle"
My logic is way different from yours. Brakes are cheap and inexpensive. I would much rather use them and wear them out than put any bit of extra strain on an engine. Putting more strain on an engine and potentially wearing something out prematurely is an expensive fix. Not to mention time consuming and also takes your vehicle away for days to weeks.
"As far as riding the brakes down a hill that's not good which is why your Pathfinder is downshifting. It's slowing you down by doing the same as someone who had a stick."
As for going down hill I am coasting, not riding the brakes. This is a short open stretch in which case i'm only using the brakes at the end of it. If i was riding the brakes while coasting I would not have it in gear to downshift in the first place.
I think I solved my own question by recording a little bit of data. This all started with the notion of keeping my rpm as low as possible, therefore saving gas. After a weeks time of shifting into N for coasting purposes and then leaving it in D for a week on the same hills. I have come to the conclusion that the RPM only varies by a minuscule amount. Either way the truck will stay around 1000 RPM or just above. The only time the RPM isn't around 1000 is on the initial downshift.
Thanks for the opinions and ideas.
"knowing is half the battle"
Jetwrangler, you are living in two extreems. If your hill has such a small grade to where you are only getting up to 60 at the bottom then engine breaking is minimal as well. You have an engine to preform two functions. One is to accelerate and the other is to declelerate. Your engine has been designed to do both in conjunction with your tranny. Race car drivers use the downshift to slow their entry into a turn along with breaking to minimize brake fade. That is an extreme in itself and they do not even go up or down hills. I have driven tractor trailers for a few years and you would never go down any grade without using your engine break. The reason for this is break fade and the risk of getting killed by falling of the mountain.
Your engine will not have any excessive wear at all since on downshifts it basicly turns off the fuel supply and the parts are just running their course. The transmission does all of the work and the gears are slowing the vehicle down. There is no excessive wear in this function only a conversion of energy. If you keep your transmission fluid and your transfer case fluid up to date and clean then you will have no problems at all.
As to your five speed method of pushing in the clutch and leaving it disengadged going down hill without reengadging each gear to slow yourself down, well, you are wearing down your clutch springs and the result will be a spongy clutch deployment in the long run. I know the counter argument here is that you would be wearing down your clutch plates; however, the plates are designed to take this abuse but the springs are not.
Wear and tear is a natural function of a car and parts are designed to take the abuse for intended purpose and time. The design of our vehicles (Pathfinders) is so that they have some off road capabilties which is a bit harder on the parts of the vehicle, including engine & transmission. Your vehicle has a better wear and tear factor then most vehicles on the market. Your truck wil take that hill with ease and go down it the same way. So do yourself a favor and let the vehicle do its job and do not try to overthink what much more knowledgable people have already done for us, the Engineers at Nissan.
Your engine will not have any excessive wear at all since on downshifts it basicly turns off the fuel supply and the parts are just running their course. The transmission does all of the work and the gears are slowing the vehicle down. There is no excessive wear in this function only a conversion of energy. If you keep your transmission fluid and your transfer case fluid up to date and clean then you will have no problems at all.
As to your five speed method of pushing in the clutch and leaving it disengadged going down hill without reengadging each gear to slow yourself down, well, you are wearing down your clutch springs and the result will be a spongy clutch deployment in the long run. I know the counter argument here is that you would be wearing down your clutch plates; however, the plates are designed to take this abuse but the springs are not.
Wear and tear is a natural function of a car and parts are designed to take the abuse for intended purpose and time. The design of our vehicles (Pathfinders) is so that they have some off road capabilties which is a bit harder on the parts of the vehicle, including engine & transmission. Your vehicle has a better wear and tear factor then most vehicles on the market. Your truck wil take that hill with ease and go down it the same way. So do yourself a favor and let the vehicle do its job and do not try to overthink what much more knowledgable people have already done for us, the Engineers at Nissan.
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jetwrangler
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Wow, thanks I guess. I had concluded to leave it in gear and let the truck do the work a month ago. But, it is always nice to see how others think. As to the over thinking how do you think innovations and new ideas come about? Ordinary people (not engineers) have made some pretty ridiculous discoveries. My background consists of 4 degrees, I am a FAA certified Aircraft Mechanic, and I now deal with industrial generators. If you think I put all my faith in an engineer you are crazy. Example, why are oil filters in the worst possible place on 90% of cars. Answer: an engineer designed it that way. Why: because the engineer only had to design the engine, not what it went in, another engineer did that. If that’s not enough for you go look at the civil engineer field, some pretty horrible disasters have happened in bridges and buildings that yes engineers designed. I respect Engineers and several are close friends and colleagues. But that doesn’t change my thought of don’t believe what you’re told, double check and find answers for yourself.
BTW: I drive a pathfinder not a semi-truck, 40 tons (loaded semi) is a whole other story when considering brake fade. My Nissan weighs 2.24 tons roughly.
BTW: I drive a pathfinder not a semi-truck, 40 tons (loaded semi) is a whole other story when considering brake fade. My Nissan weighs 2.24 tons roughly.
I do have a few degrees of my own (Graduate Level) but education does not mean or guarantee the usage of common sense. All I'm saying is that you are over analyzing a small problem.
Most innovations come from highly educated people with degrees in their field. The few that have done so without, well, they are few.
The Pathfinder is now (in its current form) 6 years in the making. Most of the quirks have been found and dealt with and you would be able to find out what they are pending on the year and model you drive (Example: Radiator leak resulting in transmission fluid contamination). Sure engineers make mistakes and will be scrutinized for them; however, we make more of them and pay for them.
Your Pathy might only weight a bit over 2 ton's but believe me you are just as susceptible to break fade with failure then a 40 ton truck is. Of course not on your small hill, but in all of our wonderful mountain regions in the US and elsewhere the dangers are lurking with grades as high as 12% (12% indicates a drop or rise of 12 feet per 100 feet distance; The trig function of the angle is the Tangent = 12"/100" = 0.12 and the angle would be approximately 7 degrees.). If you were to travel 1 mile on a 12% grade you would have changed your altitude by almost 634ft and your ears would be popping like in the decent of an airplane. If you apply Physics and "Newton's law of motion" you can figure out how fast you might be traveling after having started at 40Mph.
I've seen overloaded vehicles or unsafe trailering result in serious accidents and most of those are regular folks (such as yourself I assume) with everyday vehicles overestimating or just not using common sense in their endeavors.
Anyway, I hope your problems or concerns stay as small as they seem to be and remember to do things smarter and not harder!
BTW: Just because I used to drive big trucks doesn't mean I'm uneducated. I'm also a bit surprised about the vagueness of the description of your original problem. If you are an engineer (you speak of colleagues) then I understand why you have such little faith in them.
Most innovations come from highly educated people with degrees in their field. The few that have done so without, well, they are few.
The Pathfinder is now (in its current form) 6 years in the making. Most of the quirks have been found and dealt with and you would be able to find out what they are pending on the year and model you drive (Example: Radiator leak resulting in transmission fluid contamination). Sure engineers make mistakes and will be scrutinized for them; however, we make more of them and pay for them.
Your Pathy might only weight a bit over 2 ton's but believe me you are just as susceptible to break fade with failure then a 40 ton truck is. Of course not on your small hill, but in all of our wonderful mountain regions in the US and elsewhere the dangers are lurking with grades as high as 12% (12% indicates a drop or rise of 12 feet per 100 feet distance; The trig function of the angle is the Tangent = 12"/100" = 0.12 and the angle would be approximately 7 degrees.). If you were to travel 1 mile on a 12% grade you would have changed your altitude by almost 634ft and your ears would be popping like in the decent of an airplane. If you apply Physics and "Newton's law of motion" you can figure out how fast you might be traveling after having started at 40Mph.
I've seen overloaded vehicles or unsafe trailering result in serious accidents and most of those are regular folks (such as yourself I assume) with everyday vehicles overestimating or just not using common sense in their endeavors.
Anyway, I hope your problems or concerns stay as small as they seem to be and remember to do things smarter and not harder!
BTW: Just because I used to drive big trucks doesn't mean I'm uneducated. I'm also a bit surprised about the vagueness of the description of your original problem. If you are an engineer (you speak of colleagues) then I understand why you have such little faith in them.
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