Coast in-neutral vs in-gear: I've been challenged to show the numbers

[Vekke]

For those who are already at the extreme fuel consumption figures with your cars:
You can calculate the speed when its more fuel efficient to start using engine braking vs coast in neutral.
Get your idle fuel consumption
Use your average fuel consumption or your fuel consumption target for that tank.
calculate the speed when you will burn more fuel when coasting in neutral than your target fuel consumption

Now the engine braking under that speed limit which you get is more fuel economical if:
- you need to stop for sure
- you shut down the engine when you stop

If you use EOC this is not valid for you.

Like people have said there is no one answer and there are always many factors which is best way. General rules still follows:
-EOC is the best option
-Neutral coasting second best in most cases
-engine braking, when need to slow down more than coasting in neutral does slow you down.

So try to save the momentum as much as possible like said before.

[TheIVJackal]

I was just thinking of something yesterday, when the car still isn't warmed up, is it better to coast in gear or coast in neutral? Assuming we want the car to get up to temperature as fast as possible, what would be more beneficial? Which heats up the car faster? I hope i'm coming through clear.
- Aaron

[user removed]

I start off in my neighborhood by coasting in neutral as much as possible. Even with cold start higher fuel consumption I see the MPG reading stabilize and even climb when I am coasting, so for my Fiesta coasting in neutral works even from a cold start. I can usually recover the average mileage within 4 miles of initial cold start, even though I am getting on a 55 MPH highway and climbing a 10 foot vertical just getting out of my 90 foot driveway.

regards
Mech

[euromodder]

Originally Posted by TheIVJackal

Assuming we want the car to get up to temperature as fast as possible, what would be more beneficial? Which heats up the car faster?

Idling will heat it up faster - as the engine would still get some fuel to burn.
If you "coast in gear" i.e. use engine braking, there's no fuel going into the engine - provided you don't have an ancient car

As PaleMelanesian already wrote, it's best (for fuel economy) to keep the engine as cold as possible.

I coast in neutral with the engine on - as Hägar can't be bump started.

[user removed]

If I coast (engine on) it takes slightly longer for the engine to warm up, but I am getting better mileage since the available waste heat is lower.

regards
Mech

[serialk11r]

Originally Posted by Old Mechanic

If I coast (engine on) it takes slightly longer for the engine to warm up, but I am getting better mileage since the available waste heat is lower.

regards
Mech

Intuitively this is right, the heat rejection rate doesn't go down that much after it's warm anyways since the flame temperature and exhaust temperature are much, much higher than coolant temperature.

But what about lubrication? My engine makes groaning sounds when it's cold that go away when the oil warms up...very disconcerting :/ Wasting a bit of gas at low load letting the engine warm up faster makes me feel better about my bearings. Maybe I just need a 5W-20 instead of a 10W-30.

[Rex Hooligan]

I've quit reading the last half of the posts, just too many. Little crusty here an there as well. I'm not going to answer the OP question but only provide my experiences.

I'm new here. I've been trying to save fuel for a few months now. I'm driving a Matrix 2.5 auto. There are 2 sections in my daily drive where I have been bumping it into neutral (given fav traf cond) to coast. These are gradual down hills about a mile+ long. There is no question in my mind that if I bring my car up to 60 and coast in neutral I will go at least double or more the coasting distance than if I left my car in gear. If I can coast for an extended period I will take it out of gear but if not I'll leave it in neutral. I can see from my scangage that my trip milage is better for this. No hard data, just anecdotal observations. If I coast in gear then the engine drags my roll distance way down and I need to accelerate again to bring it up to speed for the other half of the section. It seems to me that the fuel I need to bring my car up to speed again to start another in gear coast is more the the whole out of gear coasting would take just at idle. Swagging...one min of idle VS and acceleration from 40 to 65mph. I'm guessing the one min of idle but I'm open to comments and suggestions.

[Gealii]

Originally Posted by Rex Hooligan

I've quit reading the last half of the posts, just too many. Little crusty here an there as well. I'm not going to answer the OP question but only provide my experiences.

I'm new here. I've been trying to save fuel for a few months now. I'm driving a Matrix 2.5 auto. There are 2 sections in my daily drive where I have been bumping it into neutral (given fav traf cond) to coast. These are gradual down hills about a mile+ long. There is no question in my mind that if I bring my car up to 60 and coast in neutral I will go at least double or more the coasting distance than if I left my car in gear. If I can coast for an extended period I will take it out of gear but if not I'll leave it in neutral. I can see from my scangage that my trip milage is better for this. No hard data, just anecdotal observations. If I coast in gear then the engine drags my roll distance way down and I need to accelerate again to bring it up to speed for the other half of the section. It seems to me that the fuel I need to bring my car up to speed again to start another in gear coast is more the the whole out of gear coasting would take just at idle. Swagging...one min of idle VS and acceleration from 40 to 65mph. I'm guessing the one min of idle but I'm open to comments and suggestions.

do you happen to be using your torque converter when accelerating?
If not that would be why your not seeing much of an improvement. i do pulse and glide in my grand am autotrans and if i dont use my TC to accelerate i do see negative results. i do 45-63mph pulse and glides. My favorites are DFCO and the fact that my tranny switches into N when coasting in gear.

[user removed]

Originally Posted by serialk11r

Intuitively this is right, the heat rejection rate doesn't go down that much after it's warm anyways since the flame temperature and exhaust temperature are much, much higher than coolant temperature.

But what about lubrication? My engine makes groaning sounds when it's cold that go away when the oil warms up...very disconcerting :/ Wasting a bit of gas at low load letting the engine warm up faster makes me feel better about my bearings. Maybe I just need a 5W-20 instead of a 10W-30.

My Ranger made horrific noises until I looked at it carefully and found the exhaust heat shield had cracks near the connecting clips. Found it by banging the exhaust system with my hand. Ripped off the heat shield and it sounds just about like a new vehicle.

Not sure what a "groaning noise" would actually sound like but mine was induced by certain periods of resonance that was much more prominent at certain RPM. This is a 15 year old factory exhaust. I think it is stainless steel and I can find no reason to replace it with the noise problem cured.

The exhaust manifold heat shield would be my best guess as the cause of your noise, but any guess is just that, a guess. Based on a lot of experience the guess becomes somewhat educated.

As far as cold oil pressure, that is not a concern, at least to me, after seeing my (long gone) 1937 Ford that produced 60 PSI of oil pressure cranking at 100 RPM on the original 6 volt system and starter motor. You have plenty of oil pressue in a cold engine at any RPM above 100 which you will never see in any modern engine, even cranking. After the first second of turning the key to the crank position, on initial start, you have plenty of oil pressure.

regards
Mech

[Rex Hooligan]

Originally Posted by Gealii

do you happen to be using your torque converter when accelerating?
If not that would be why your not seeing much of an improvement. i do pulse and glide in my grand am autotrans and if i dont use my TC to accelerate i do see negative results. i do 45-63mph pulse and glides. My favorites are DFCO and the fact that my tranny switches into N when coasting in gear.

So if I understand correctly - I need to be using the TC when accelerating. How do I know if I'm using the TC under acceleration? I try not to push the RPMs over 2500when accelerating thinking that is generally better for FE. I haven't read up on pulse and glide techniques, I'll search for a thread or if you can offer one that would be helpful. I don't know what DFCO is either. I know what a metric cresent wrench is but I'm a bit of a nube with this ecco stuff. Appreciate your help.

Oh another thought. In my 2010 Matrix,is the fuel really shutting off when I coast in gear? I'm under the general assumtion that it is. The SG reads 9999 so I thinking it is detecting the fuel is shut off during this time.

Too many questions LOL