Is it more efficient to throw a std TDI into neutral and coast down a hill or to put it in a lower gear and coast that way? I've always assumed the former but someone recently proposed the theory that in gear is more efficient.
coast or not?
- Thread starter everyman
- Start date
NB_TDi
Vendor
Ah man not again!
40X40
Experienced
Short version:
It depends on how steep and long the hill is, how fast you can go, traffic and what you want to do at the end of the hill......etc. ad nauseum.
There is no pat answer.
Bill
It depends on how steep and long the hill is, how fast you can go, traffic and what you want to do at the end of the hill......etc. ad nauseum.
There is no pat answer.
Bill
X CELL TDI
Member
Isn't it better and easier to asnwer the question asked instead of treating fellow members as if you get angry at them when they ask something that we all know? just because he owns a tdi doesn't means he knows everything i know theres a search feature but a simple answer like: hi everyman it is proven you will get better mpg if you coast in gear do it!. instead of burning him with this ones:
Been beat to death. Do a search. or the classic Ah man not again! we here to help not to treat fellow tdi owners like that my .02
Been beat to death. Do a search. or the classic Ah man not again! we here to help not to treat fellow tdi owners like that my .02
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Digital Corpus
Top Post Dawg
There are many a thread, and several long threads discussing the merits and disadvantages of each beyond the point where the phrase "beating a dead horse" becomes a cliche.
40X40
Experienced
X CELL TDI said:
Are you from the vortex?
Troll somewhere else.Bill
X CELL TDI
Member
Right but an answer like my man 40x40 up there was in order instead the "search it you fool" types I mean maybe he wasn't a member or maybe he didn't know about fred's 1-2-3-4-10 years ago when this question became something considered as a dead thread, i've seen often when a noob ask something simple to answer and gets search it! or not again! or man we discussed that X years ago, look at my member date up there feb 2010 but i been reading fred's since 2002 just became member because just got my tdi in feb 2010 always wanted one but always ended buying big vehicles and my project cars always where for drag, say <12 sec .25 miles but now im working on this tdi and man i was stupid not to get one back in 2002 i love my jettaDigital Corpus said:
X CELL TDI
Member
no im not and i was giving your answer the thumbs up i guess i type slow.........but i drive fast hehehe.. not trying to piss anybody off but i think i have a point, we are a club maybe more than that i think theres more knowledge on this site than in vw archives why? our members have put the miles, time and sweat to tdis and its not right to let a fellow member on their own when a simple question can be answered right on the spot if it was a technical question like say how do i change my clutch or how do i do my own tb that we can tell them search for that cuz theres a some step by step threads here.... i think we shoul help with simple things like that40X40 said:Are you from the vortex?
Bill
JonFord
Veteran Member
X-CELL-TDI.
I would bet if someone did a study of the second post in all of the TDICLUB forum posts, you would find that 1/2 of them have the word search in that #2 post.
With that in mind, maybe the powers to be should just shut the ability to post down and make a statement to" just do a search, it is in here some place".
JonFord
I would bet if someone did a study of the second post in all of the TDICLUB forum posts, you would find that 1/2 of them have the word search in that #2 post.
With that in mind, maybe the powers to be should just shut the ability to post down and make a statement to" just do a search, it is in here some place".
JonFord
jimbobb2
Veteran Member
The coasting is a dead horse. In a nutshell, it depends on the situation which is the best way to go. There truelly is no such thing as coating in gear, it is decelleration. When you are coasting, the engine is idling which burns fuel. When you let off the throttle in gear you use no fuel. If you are going short distance, stay in gear. If you are coasting longer distance (I have a 1/2 mile coast into town every day) go to nuetral and gain the distance. I know that there will be disagreement on what I have said, but it is what works for me in this area of the country on the roads I drive. Experiment and find out what works for you.
This a problem on every forum. people naturally ask the same questions over and over. I agree they should search, but people should not be rude to them. A short answer with the request that the OP do a search should suffice.
But I admit to being rude on other forums also, just because some questions are asked so often, you know the asker could not have looked hard.
Not saying that's the case here. This is the first coasting thread I've seen in a while.
/have not searched for coasting threads
//one of my first post was in a coasting thread in 2001.
///old user name James2
But I admit to being rude on other forums also, just because some questions are asked so often, you know the asker could not have looked hard.
Not saying that's the case here. This is the first coasting thread I've seen in a while.
/have not searched for coasting threads
//one of my first post was in a coasting thread in 2001.
///old user name James2
NB_TDi
Vendor
There was a thread that happened not that long ago, I seem to remember name calling and harsh words.
Has nothing to do with nOObS asking the same questions, it's just the fact that this topic always ends the same.
Has nothing to do with nOObS asking the same questions, it's just the fact that this topic always ends the same.
09R/T
Veteran Member
It all depends on the situation...which has kinda been touched on above.
If the grade is steep enough that leaving it in gear yields no loss in speed or a slight gain....then leave it in gear. Diesels burn 0 fuel when trying to decel.
However, if there is an uphill portion right after the downhill (valley), then it may be more economical to coast down the hill and gain speed at no cost to economy, then use that gain of speed to use less fuel climbing the hill directly after.
If the grade is steep enough that leaving it in gear yields no loss in speed or a slight gain....then leave it in gear. Diesels burn 0 fuel when trying to decel.
However, if there is an uphill portion right after the downhill (valley), then it may be more economical to coast down the hill and gain speed at no cost to economy, then use that gain of speed to use less fuel climbing the hill directly after.
BigBadThor
Veteran Member
- Joined
- Jan 28, 2010
- Location
- Toronto, ON
- TDI
- 2003 Tornado Red Jetta Wagon GLS (sold); 2014 GSW Wolfsburg Edition CPO TDI
Holy run-on sentences Batman!X CELL TDI said:
It is simple, really. Fuel burn rate at idle compared with the difference in decel rate in neutral vs. in-gear (with the drag of the trans/engine motoring via reverse power flow from wheels to crankshaft).
At the end of the coasting event, how much fuel would you need to burn to make up the speed you lost by leaving it in gear, and is that amount of fuel more than the fuel you burned idling for the duration of the coasting event?
We need someone to get the above data vs. pulling opinions out of a dark place.
At the end of the coasting event, how much fuel would you need to burn to make up the speed you lost by leaving it in gear, and is that amount of fuel more than the fuel you burned idling for the duration of the coasting event?
We need someone to get the above data vs. pulling opinions out of a dark place.
thebigarniedog
Master of the Obvious
x2. To the OP, here is the link:NB_TDi said:
http://lmgtfy.com/?q=tdiclub%3A+coasting+in+gear
Welcome to the tdiclub and Good Luck.
40X40
Experienced
Tec80 said:
If all hills were the same you would then have some useful information.
There are some hills where you have an acel rate when coasting in gear!
Bill
ruking
Top Post Dawg
- Joined
- Mar 27, 2003
- Location
- San Jose area, CA
- TDI
- 2003 VW Jetta, 5 M, Reflex Silver: 09 Jetta, 6 Sp DSG, Candy White: 12 VW Touareg, 8 Sp A/T, Flint Gray
Actually yours is a very reasoned approach. We have a pretty "real world" example. To go to and from Tahoe, CA, sea level to 7085 ft and return http://en.wikipedia.org/wiki/Donner_Pass. Basically we get 3/4 mpg better on the "down hill". Down hill can be described as 150 miles or soTec80 said:
. However, when you average the mpg for the entire trip. ....It be "normal" !!!?? But you got to like going up hill when you are passing the majority of V-8's. You also know they are sucking WAY more fuel than a TDI
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jimbobb2
Veteran Member
No contest is not really true. If you are slowing down while in gear then you will have to accellerate to get back up to speed. I have a 1/2 to 3/4 mile coast (in nuetral) every day coming into town. I start at 60 mph and let the car slow down to 45 mph and then 40 mph as the speed limit is posted. In gear I have to add throttle as not to impede traffic. You burn .3 of a gallon per hour at idle and none while decellerating in gear (you are not coasting if the engine is dragging speed off). My 45 second coast uses approximately half of an ounce of fuel, if I have to use the throttle 9 seconds to maintain speed (assuming 20 mpg on accelleration) I am using .9 of an ounce of fuel. Please check my figures as I may be wrong (after a 16 hour day at work). All I am saying is that it depends on what the circumstances are as to what is going to use the least fuel. Please feel free to correct me if I am wrong.RalphVa said:
Ralph, please read my post carefully. The engine is not frictionless. It takes energy to spin it. If it didn't, your battery and starter could be much smaller and lighter than they are. When you are coasting in gear you are spinning the engine using the inertia of the car. Some inertia is lost while doing this, MORE inertia than is lost when in neutral.
Think of it this way. 2 identical 6-speed JSW TDIs coasting downhill next to each other, cresting a hill at 50MPH. One puts his car in neutral, the other leaves it in 6th. The guy in neutral will slowly pull away from the in-gear guy during the coasting event, and at the end of the hill will be traveling faster than the in-gear guy. He can coast longer before falling below the speed limit. So, the in-gear guy must then "turn the fuel back on" earlier, burning more fuel than the neutral guy. Depending on hill, speed, etc. The higher the RPM during coasting in-gear, the more inertia is lost.
Think of it this way. 2 identical 6-speed JSW TDIs coasting downhill next to each other, cresting a hill at 50MPH. One puts his car in neutral, the other leaves it in 6th. The guy in neutral will slowly pull away from the in-gear guy during the coasting event, and at the end of the hill will be traveling faster than the in-gear guy. He can coast longer before falling below the speed limit. So, the in-gear guy must then "turn the fuel back on" earlier, burning more fuel than the neutral guy. Depending on hill, speed, etc. The higher the RPM during coasting in-gear, the more inertia is lost.
Ski in NC
Top Post Dawg
If descending a hill and you want to maximize speed at the bottom, and don't need to brake, then use neutral and coast.
If descending a hill and it is steep, or a curve at the bottom, or a stop at the bottom, leave in gear and let the engine brake at zero fuel.
If you find yourself using the brakes on the downhill, you should have engine in gear.
If descending a hill and it is steep, or a curve at the bottom, or a stop at the bottom, leave in gear and let the engine brake at zero fuel.
If you find yourself using the brakes on the downhill, you should have engine in gear.
40X40
Experienced
Ski in NC said:
BINGO!!
Or in simpler words, IT DEPENDS on the circumstances.
Bill
jimbobb2
Veteran Member
The next question comes with the thoughts of upper cylinder lubrication. When in gear and the fuel shut off, you are not getting any upper cylinder lubrication. Is this causing any additional wear? I am sure that this is so little that you couldn't measure it, but I am thinking long term or if you had a long steep grade (such as the mountains). The next question is......does the fuel actually shut off when in gear? I rolled down a slight hill and let the clutch out in second to start my 10 Jetta. I never touched the throttle and pushed the clutch back in after a couple of seconds and the car was running. That seems to indicate that there is some fuel still going through the engine.
40X40
Experienced
jimbobb2 said:
Above idle speed and with the 'throttle' closed, all fuel is shut off.
When you pushed in the clutch, the engine slowed below idle speed and fuel flow was resumed to keep the engine from dying.
Simple.
Bill
Dankcorey22
Veteran Member
when you have your foot off the throttle and the rpms is above 1200 all fuel is shut off like ^^^ when you push the clutch in the engine is idleing which uses fuel to keep from dieing
Ski in NC
Top Post Dawg
Upper cylinder lubrication is not a concern regarding coasting. The lube action for the top ring comes from crankcase lube oil spread upwards from the piston in its down position. Probably a better lube situation when rpms are up, as oil film is thicker then. Nothing to do with whether engine is fueling or not.
jimbobb2
Veteran Member
OK. These are some things I was not sure of. Thank you guys for your knowledge of these cars.