coasting in neutral w/ a manual...good or bad for the engine - Page 5 - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > TJ Wrangler Technical Forum > coasting in neutral w/ a manual...good or bad for the engine

Introducing MONSTALINER™ UV Permanent DIY Roll On Bed LineFS: 2007-2013 Jeep Wrangler "HALO" Angel Eye KitClayton Off Road - Come see us at these events!

Reply
Unread 08-17-2010, 07:34 AM   #61
Sweeney
Registered User
2006 LJ Wrangler 
 
Join Date: Aug 2006
Location: Spencer, MA
Posts: 1,299
Quote:
Originally Posted by mikevsgeek View Post
Compression braking is supposed to be used to help maintain vehicle speed down long grades vs constantly applying the brakes and possibility getting into a overheating brake situation.

By coasting down a hill in neutral, you risk putting your jeep in an over speed condition. Lets say you are doing 70mph down hill, which for me with the 4.0 w/ NV3550, 4:10s and 33s, is about 2000 rpms. All of my engine accessories are running at the correct speed to maintain the proper engine environment (water pump, oil pump) and the input shaft on my transmission is also spinning at the correct rate so that proper lubrication can occur. Now lets say I coast down the hill in neutral, my engine is idling at 800rpm give or take so now my engine may not be getting the correct cooling or oil lubrication that it needs and my input shaft into the transmission is no longer spinning meaning that my transmission might not be getting the lubrication that it needs. So then lets say I coasted down the hill in neutral and towards the bottom of the hill I'm doing 75mph and I put it in 5th and let of the clutch, I'm going to risk the possibility of put a shock load on my engine, transmission and drive line components.

The rule of thumb for going down hills is that you should be in the same gear that you would need to be to go up the hill.

And if your so worried about your MPG, you probably shouldn't have bought a jeep in the first place
Again, you have completely missed the point or just failed to read/comprehend the circumstances where coasting down hill is applicable.

You are coasting TO GO FASTER THAN YOU WOULD IF COMPRESSION BRAKING. YOU ARE TRYING TO GOT FASTER, NOT SLOW DOWN.

If you "shock load" any components in the process of engaging a gear after coasting then you don't know how to properly operate a manual transmission vehicle. Look up 'RPM matching'.

Who's "rule of thumb"? If the climb requires that the Jeep be in 3rd gear how does that dictate the decent should be in 3rd gear?

Your comment about the desire to improve fuel economy is simply ignorant.

Sweeney is offline   Reply With Quote
Unread 08-17-2010, 09:47 AM   #62
mightydog78
Registered User
2013 JK Wrangler 
 
Join Date: Jan 2009
Location: Charlotte/Winston-salem, NC
Posts: 1,987
i coast in neutral in my auto sometimes..
__________________
2013 JKU Sahara

Charlotte, NC / Southport, NC

Mechanical Engineer
mightydog78 is offline   Reply With Quote
Unread 08-17-2010, 12:38 PM   #63
mikevsgeek
Registered User
2002 TJ Wrangler 
 
Join Date: Sep 2004
Location: Minot, North Dakota
Posts: 322
Quote:
Originally Posted by Sweeney View Post
Again, you have completely missed the point or just failed to read/comprehend the circumstances where coasting down hill is applicable.

You are coasting TO GO FASTER THAN YOU WOULD IF COMPRESSION BRAKING. YOU ARE TRYING TO GOT FASTER, NOT SLOW DOWN.

If you "shock load" any components in the process of engaging a gear after coasting then you don't know how to properly operate a manual transmission vehicle. Look up 'RPM matching'.

Who's "rule of thumb"? If the climb requires that the Jeep be in 3rd gear how does that dictate the decent should be in 3rd gear?

Your comment about the desire to improve fuel economy is simply ignorant.
I never said you would go faster by using compression brakes, I simply stated the intended purpose of using compression brakes. Its not intended to stop a vehicle but help maintain vehicle speed down long grades.. thus how could it make you go faster?

I didnt say that it WOULD cause a shock load by coasting and then going into gear, I said it would cause a possibility of a shock load.

and the rule of thumb? if you are going up a 7% grade and need to be in third gear, you should be in 3rd going down it. going down the same hill if you are coasting and need stop, you are going to have to figure out what gear you want, rpm match, get it in gear, slowly release the clutch and then apply the brakes.. hopefully you didn't just drive into the back of the stopped 18 wheeler.. if you were in 3rd gear and going down the grade at the appropriate speed you would have been in control of your vehicle the entire time and stopping wouldn't have been an issue.

I never said anything about improving mpg, I said that people shouldn't buy jeeps if they are worried about how many mpg they are getting.

What I am stating is how you should be driving by the book. Does that mean you cant coast down a hill? No. The simple question was asked "Is coasting in neutral good or bad for the engine?" the simple answer is No, the engine is happy running at idle speed all day long.. BUT you are putting other components of the vehicle at RISK for premature failure by putting your vehicle in an over speed situation like that.
mikevsgeek is offline   Reply With Quote
Unread 08-17-2010, 12:55 PM   #64
Phreaq
Registered User
2000 TJ Wrangler 
 
Join Date: Mar 2008
Location: , CA
Posts: 206
mikevsgeek > Engine idles just over 1k while the vehicle is rolling out of gear, and output shaft, t-case, and trans gears are turning due to the rear wheels turning.
Compression brakeing is for BOTH slowing down to a stop (commonly referred to as "downshifting", and to keep a safe downhill speed (usually there is a sign stated use low gears. Still there is a point where being in gear requires to use slight throttle while going DH to maintain speed, THIS is where "N" is commonly used, unless "N" also is slowing you down.


As stated, you must know how to reengage the trans to prevent "shock", just as with climbing a hill in 4th and dropping to 3 takes a little play with the throttle (or a double clutch may work, I've never done it other then my F100) to match revs.


nitecop, jeepnblake > My TJ temp droped to the bottom during a decent, but it was a bit chilly out and my dual core bass/copper radiator over cools. I used some cardboard to block some wind. Even in 105°f weather I will not reach proper operating temp while moving. My e-fan is off all the time, unless I am not moving for a longer then a red light.

Last edited by Phreaq; 08-17-2010 at 11:10 PM..
Phreaq is offline   Reply With Quote
Unread 08-17-2010, 04:46 PM   #65
bruteboy
Registered User
 
Join Date: May 2010
Location: british columbia ca
Posts: 470
Quote:
Originally Posted by OlllllllllO View Post
I coast down hills with my transition in neutral....I hold the clutch in (while in neutral) .... is that bad????
yes,with the transmission in neutral and the clutch disengaged,
mainshaft lubrication will be inadequate and cause transmission damage.
if you coast in neutral,take your foot off the clutch(engage clutch)so the engine can turn the gears to lubricate the mainshaft.
bruteboy is offline   Reply With Quote
Unread 08-18-2010, 11:42 AM   #66
tha_Toad
Member
 
tha_Toad's Avatar
2003 TJ Wrangler 
 
Join Date: May 2010
Location: Fort Riley, Kansas, Kansas
Posts: 343
I just drive mine and refill it when its empty but i see a difference in coasting i coast alot more than i use to and now im getting 17-18 mpg
__________________
Jeep Wrangler - a brick powered by a hamster and has the aerodynamics of a house.
tha_Toad is offline   Reply With Quote
Unread 08-18-2010, 12:45 PM   #67
Jonny Jeep
Web Wheeler
 
Jonny Jeep's Avatar
1997 TJ Wrangler 
 
Join Date: Feb 2007
Location: Manchester, UK
Posts: 4,460
Here's how the FSM describes fueling during deceleration. Fuel is only cut off under "hard" deceleration. How hard is not defined.

"If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not supply a ground to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection."
__________________
"Giving English to an American is like giving sex to a child. He knows it's important but he doesn't know what to do with it."
Adam Cooper (19th century)

Rockauto 5% discount code can be found here... http://www.markviii.org/LOD2/products_services.htm

Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
If the link doesn't work properly, look for the service manual link under Jeep Resources at the bottom of the page.
Jonny Jeep is offline   Reply With Quote
Unread 08-18-2010, 05:43 PM   #68
Knuckelhead
AFSOC Retired
 
Knuckelhead's Avatar
2000 TJ Wrangler 
 
Join Date: Aug 2005
Location: Colorado
Posts: 14,366
Quote:
Originally Posted by Jonny Jeep View Post
Here's how the FSM describes fueling during deceleration. Fuel is only cut off under "hard" deceleration. How hard is not defined.

"If the vehicle is under hard deceleration with the proper rpm and closed throttle conditions, the PCM will ignore the oxygen sensor input signal. The PCM will enter a fuel cut-off strategy in which it will not supply a ground to the injectors. If a hard deceleration does not exist, the PCM will determine the proper injector pulse width and continue injection."
So under "normal" deceleration, your still burning fuel?...
__________________
TSB Information: http://www.automd.com/tsb/jeep_m/wrangler_mm/2000_y/
Knuckelhead is offline   Reply With Quote
Unread 08-18-2010, 07:29 PM   #69
Sweeney
Registered User
2006 LJ Wrangler 
 
Join Date: Aug 2006
Location: Spencer, MA
Posts: 1,299
Quote:
Originally Posted by Knuckelhead View Post
So under "normal" deceleration, your still burning fuel?...
Correct.
Sweeney is offline   Reply With Quote
Unread 08-18-2010, 07:52 PM   #70
Knuckelhead
AFSOC Retired
 
Knuckelhead's Avatar
2000 TJ Wrangler 
 
Join Date: Aug 2005
Location: Colorado
Posts: 14,366
Quote:
Originally Posted by Sweeney View Post
Correct.
Thank you. Thats the way I've always understood it...
__________________
TSB Information: http://www.automd.com/tsb/jeep_m/wrangler_mm/2000_y/
Knuckelhead is offline   Reply With Quote
Unread 08-18-2010, 10:21 PM   #71
phillies4752
Web Wheeler
 
phillies4752's Avatar
2005 LJ Wrangler 
 
Join Date: Nov 2008
Location: West Chester, PA
Posts: 1,038
is there any proof that it hurts the tranny to coast in neutral? Has anyone pulled apart their tranny do find out?? hahaha ahhh well im gonna keep doing what im doing and coast down hills in neutral thank you very much! If someone has some pictures to prove that the tranny is getting damaged by doing this please post them!!! I am VERY interested! haha
phillies4752 is offline   Reply With Quote
Unread 08-19-2010, 10:02 AM   #72
Jonny Jeep
Web Wheeler
 
Jonny Jeep's Avatar
1997 TJ Wrangler 
 
Join Date: Feb 2007
Location: Manchester, UK
Posts: 4,460
I expect it depends just what distance/speed you are coasting.

Short distances shouldn't present problems, but there's a reason the transfer case should be in neutral and the transmission in gear (manual) or Park, when the TJ is towed.
__________________
"Giving English to an American is like giving sex to a child. He knows it's important but he doesn't know what to do with it."
Adam Cooper (19th century)

Rockauto 5% discount code can be found here... http://www.markviii.org/LOD2/products_services.htm

Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
If the link doesn't work properly, look for the service manual link under Jeep Resources at the bottom of the page.
Jonny Jeep is offline   Reply With Quote
Unread 08-19-2010, 10:11 AM   #73
Donato_XIII
Registered User
2013 JK Wrangler 
 
Join Date: Mar 2010
Location: Vancouver, B.C.
Posts: 125
Quote:
Originally Posted by Mean Max View Post
Coasting out of gear or "free-wheeling" is a lousy habit to develop. Should the need to accelerate or decelerate suddenly happen you'll invariably struggle to figure out what gear to be in or how to quickly respond.

You should ALWAYS be in the correct gear for the speed of the vehicle, no exceptions.

Max
^

I didnt read past page 1 but IMO you should always be in gear (except maybe stopped at a light) If your using gears properly you shouldnt get any resistance going down hills. If you're engine braking even in 5th gear going down a hill, you might wanna slow down.
Donato_XIII is offline   Reply With Quote
Unread 08-19-2010, 10:56 AM   #74
Sweeney
Registered User
2006 LJ Wrangler 
 
Join Date: Aug 2006
Location: Spencer, MA
Posts: 1,299
Quote:
Originally Posted by Donato_XIII View Post
^

I didnt read past page 1 but IMO you should always be in gear (except maybe stopped at a light) If your using gears properly you shouldnt get any resistance going down hills. If you're engine braking even in 5th gear going down a hill, you might wanna slow down.
Again, we're not talking about engine braking.
Sweeney is offline   Reply With Quote
Reply

Tags
better economy , better mileage , coasting , driving , in gear , manual , miles per gallon , mpg , neutral
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.