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Unread 08-15-2010, 02:02 AM   #31
bruteboy
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coasting downhill with the engine running will not cause any engine or transmission damage.
coasting downhill with the engine NOT running WILL cause transmission damage in your jeep
many heavy truck transmissions WILL be damaged if coasting (engine running or not) as stated in the operators manual.
heavy truck clutches can also be damaged from coasting under certain conditions.

it is unlikely you will get any mpg increase from coasting in neutral down hills(sounds like a good one for mythbusters)


Last edited by bruteboy; 08-16-2010 at 12:52 AM..
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Unread 08-15-2010, 02:17 AM   #32
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Quote:
Originally Posted by krawler510 View Post
Who seriously made that law? Seems a bit tough to enforce. Anyway, I'm willing to say that 99% of people respond to emergency situations by slamming on the brakes, even when they should hit the gas.

Do you guys really down shift through all of the gears when slowing down?
Not really hard to enforce after an accident. Most cars nowdays will record such data as steering input, if seatbelts are connected, brakes, throttle, transmission, and speed.
A far as do I downshift when stopping, it depends on what I am driving, and other variables. When I am driving anything heavy you bet I do.
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Unread 08-15-2010, 02:27 AM   #33
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if anybody knows of big bear mountain here in California, i coasted from the top on the mountain to the bottom and drove home (124 miles) and only used up a quarter tank of gas. pretty damn good in my books

but i DO NOT have a manual, so no quoting me about anything manual
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Unread 08-15-2010, 05:06 AM   #34
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Quote:
Originally Posted by Sweeney View Post
...
Also remember, just because you've been doing something for a long time does not mean you've been doing it well or correctly.
You said it, not me.

If you HONESTLY believe that you can do the following in 250 mS:

1. Assess the looming accident, or situation that will occur if you do not excelerate, slow down, turn, swerve, or stop
2. the information is received from your eyes to the visual cortex
3. Your brain then processes said information, and makes a decision
4. information passed to the motor cortex of the brain, which triggers muscle movement

The fastest that this can be done, assuming a normal, healthy, well rested, and far above average response times .i.e Fighter Pilot, is around .44 Seconds. [NASA Technical Note, TN D-6132, cc. 1971].

So if you can do all of that in less then .250 seconds, then DAMN! You missed your calling.
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Last edited by TheHeretic; 08-15-2010 at 05:48 AM..
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Unread 08-15-2010, 05:49 AM   #35
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Quote:
Originally Posted by LuckRider View Post
That is odd because there was an article in car and driver or some other car magazine I read that too on that myth specifically. They had an engineer from Toyota say that any vehicle produced after 1995 would benefit most from being in gear because it would use 0 fuel to keep the engine alive and you need fuel to keep the engine at idle when coasting.
I was just going to add - you can see that happens on the '06 from with an AFR gauge. When I just let off the throttle and push in the clutch to coast to a stoplight ... the engine is idling at a 14.7 AFR. When I let off the throttle and coast with the clutch engaged to a stoplight ... the AFR shoots to an "unreadably lean" AFR.
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Unread 08-15-2010, 07:41 AM   #36
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Quote:
Originally Posted by TheHeretic View Post
You said it, not me.

If you HONESTLY believe that you can do the following in 250 mS:

1. Assess the looming accident, or situation that will occur if you do not excelerate, slow down, turn, swerve, or stop
2. the information is received from your eyes to the visual cortex
3. Your brain then processes said information, and makes a decision
4. information passed to the motor cortex of the brain, which triggers muscle movement

The fastest that this can be done, assuming a normal, healthy, well rested, and far above average response times .i.e Fighter Pilot, is around .44 Seconds. [NASA Technical Note, TN D-6132, cc. 1971].

So if you can do all of that in less then .250 seconds, then DAMN! You missed your calling.
Yep, I said it... in response to the several "I've been driving stick for X number of years".

None of the above should take the 4 or 5 seconds that you claim. Any of those reactions should take less than a second or so. A second is a relatively long time. My 250ms comment was 'tongue in cheek'. I have taken reaction time tests and have averaged 186ms to recognize and react. That is sensing and physically reacting.

I only coast when the situation is appropriate... never in heavy traffic. I always leave lots of room between my vehicle and any others and my usual reaction in emergency situations is to steer around.

If I were traveling down a hill at a speed where I might consider coasting I will be in top gear. If a situation arose that dictated accelerating then top gear is not the gear to be in. In this instance it would take longer to change from one gear to the next than to select the proper gear from the neutral position.

If the situation dictated aggressively slowing or stopping I would be using the brakes while disengaging the clutch so the transmission position would be irrelevant.

It's all about situational awareness.

I'll keep doing what works for me and you do the same.

My brother was an F14 pilot and instructor at the Navy Fighter Weapons School 'Top-Gun'... maybe it runs in the family.
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Unread 08-15-2010, 07:56 AM   #37
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Fair' nuff.

A top pilot? So he trained at Cold Lake Alberta then.
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Unread 08-15-2010, 11:09 AM   #38
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I would rather leave the jeep in gear, if something were to arise like needing to accelerate out of the way of something i would like to be able to mash the gas and not have to even think about clutch gear go. While it may seem second nature to perform this task due to years of driving, during a panic situation it might not go as smoothly as needed. Plus how many mpgs do you think you could really save from going to N on hills, it still is a big box on wheels last time i checked.
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Unread 08-15-2010, 02:58 PM   #39
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Originally Posted by TheHeretic View Post
Fair' nuff.

A top pilot? So he trained at Cold Lake Alberta then.
I don't recall. He last flew for the Navy in 1998.
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Unread 08-15-2010, 03:10 PM   #40
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Originally Posted by TheHeretic View Post
Fair' nuff.

A top pilot? So he trained at Cold Lake Alberta then.
I did. 1975. Head injury in '95 prevents me from ever being a pilot again though.
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Unread 08-15-2010, 03:19 PM   #41
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You will use more fuel if you shift to neutral and let the engine idle.
Most ALL EFI engines Shut off fuel completly IF the vehicle is above 20 mph, throttle is closed completly and the engine is above 1000 rpm. So as you can see you will save the most fuel if you just let off throttle completly going downhill.
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Unread 08-15-2010, 03:37 PM   #42
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Originally Posted by bruteboy View Post
it is unlikely you will get any mpg increase from coasting down hills(sounds like a good one for mythbusters)
False. When your engine is idling, you're burning fuel at a pretty slow rate. For common passenger cars, I think it's around half a gallon an hour. Lets say a full gallon for the 4.0l Jeep engine.
Now, lets say your coasting in neutral down a moderate hill at 49 miles per hour. For the period of time that you are going that speed with the engine in neutral (burning fuel at the arbitrary rate of a gallon an hour), you will be getting 49 MPG. 49 miles per hour, one gallon per hour, 49 miles per gallon.

If the hill was steep enough, you could even gain some speed and increase the MPG even further.

(I don't know exactly what Jeeps use per hour in neutral, though Sweeney can probably answer that question for us with his scan gauge.)

Now, if you were coasting in gear, you would have to coast at the correct speed and gear to keep the engine RPM's from dropping below the fuel cut off point. I doubt, on Jeeps, that it is much lower then about 2000 RPMs. If you're coasting in gear higher then that, the engine is burning NO fuel and you are effectively getting infinite MPG. Free travel.
Now, the problem with engine braking is that it's engine BRAKING. As in, there's something (all that metal crap rubbing against each other in the engine) impeding you from moving forward as fast as you should be going under other circumstances. You are actively loosing kinetic energy (speed) to maintain the engine RPMs.
Thus, I only engine brake when the hill is steep enough that if I was in neutral, I'd be going too fast from a legal and/or safety prospective and would be stepping on the brake anyway.

'97 TJ, 2.5l 4 cylinder. 20-22 MPG city/highway combined.
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Unread 08-15-2010, 04:10 PM   #43
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Originally Posted by nitecop View Post
Most ALL EFI engines Shut off fuel completly IF the vehicle is above 20 mph, throttle is closed completly and the engine is above 1000 rpm.
Do you have an accredited source to back that up for the 4.0L, TJ engine/PCM function?...
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Unread 08-15-2010, 04:15 PM   #44
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Quote:
Originally Posted by bruteboy View Post
coasting downhill with the engine running will not cause any engine or transmission damage.
coasting downhill with the engine NOT running WILL cause transmission damage in your jeep
many heavy truck transmissions WILL be damaged if coasting (engine running or not) as stated in the operators manual.
heavy truck clutches can also be damaged from coasting under certain conditions.

it is unlikely you will get any mpg increase from coasting down hills(sounds like a good one for mythbusters)
What is likely to hurt a Eaton clutch coasting with tranny in neutral?, the engine will be at idle.
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Unread 08-15-2010, 04:18 PM   #45
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Originally Posted by Pallando View Post
Now, the problem with engine braking is that it's engine BRAKING. As in, there's something (all that metal crap rubbing against each other in the engine) impeding you from moving forward as fast as you should be going under other circumstances. You are actively loosing kinetic energy (speed) to maintain the engine RPMs.
It's called compression braking, not engine friction braking...
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