Coast in gear vs in nuetral?
 

I know that it's likely been asked quite a few times before, but I couldn't find a topic in search that covered it and I'm very curious. Which usually results in better FE.

When during a coast I pop it into neutral and let the engine idle? (Using a little gas while retaining more momentum)

Or when I just let off the gas and keep it in gear as I coast, causing the fuel injectors to shut off, but the engine to add a bit of "braking" and cause the car to slow faster?

So is the loss of momentum made up for by the lack of fuel use? Or should I keep the momentum and use a little gas?

BTW, I have an 87 Ford 2.3, if that makes a difference.

ive been putting it in to N on the highway and doing P&g. ive seen much better mileage then i ever had with leaving it in gear.

P&G? What is that?

I don't want to do the shut off the engine and jump start it along the way, because I've got a rather weak clutch and don't want to wear it down any faster than I have to. I've got to make it last all summer.

pulse and glide P&G > (from glossary)Pulsa and Gluide. Its roots go way way back in FE driving. But its claim to fame has been in hybrids. Its also alot of work IMHO. But in certin cars can produce steller results. Lets say your on a stretch of road thats flat as a board. Our target speed is 60 mph. We get to 60 mph and then we begin a bleed say down to 55 mph. We then start speeding up to our 60 mph target. But we do it very very slow. In some hybrids you pick up some very lite assist from the electric motor and dont really use much of the pack. And then we start bleeding again. This is a very repetative driving style and not for the faint at heart. It takes alot of conctration and throttle control. It has alot of varibles that can be played with for diff. cars and over all driving styles. Used alot on hwy's and in city driving. The challenge for hybrid drivers is to know when to loose a P&G cycle or two to get the pack recharged. 1 5

i go from 70 down to 45-50 when i do it

Biffmeistro: This should help you make up your mind.

https://www.gassavers.org/showthread.php?t=2789

Yes, coasting in neutral will use less gas, as long as you take advantage of coasting, you will coast a lot farther than if you were in gear. Sometimes I am surprised how far I can coast in Neutral.

same here its somtimes miles on roads i know well

Coasting in neutral is better than coasting in gear. Injector shutoff only starts at relatively high speeds, makes the car slow down much quicker, and the injectors come back on at about 35.

yeah and from my brief results last night i can see a huge differance from just p&gs so im gonna do a 100 miles and see what happens

Like so many things, "it depends".

Being in N gives you more coasting distance. However, how much more distance (vs being in high gear) varies with your car (and how it's maintained). And as you mentioned, you pay for the car to "idle". How much gas that idle uses varies with a number of factors (including how many car accessories you are currently running).

Conversely, "fuel shutoff" can make "coasting in gear" something that uses no gas. If you will even get that fuel shutoff depends upon a number of factors (how the car is made, if the engine is "warmed up", what your RPMs are, etc). And furthermore, how much less you will coast in gear (vs neutral), also depends upon a lot of factors (which gear you are in, how well your engine and drive train are lubed up, drag from various car accessories you are running, etc).

So it's clearly a YMMV thing as to which is better.

My personal thoughts are that you are usually better with "coasting in gear" (specifically the highest gear you have, if you are in a manual), as long as that will still give you enough coasting distance (for example, to get to the red light). However, you are sometimes better off with coasting in neutral (and thereby paying the fuel for an idle) if/when you need/want more coasting distance than "in gear" coasting will give you.

BTW: On my CRX, I find that the drag for coasting in 5th has gotten a lot less over time, as I've worked on lubing up the car (good synthetic oil in the engine, synthetic transmission fluid in the transmission, grease up the wheel bearings, etc.). So I'm personally finding myself "coasting in 5th" a lot more than I used to.

BTW: P&G is "Pulse and Glide". i.e. quickly speed up a bit, than coast/glide for a time (then repeat when you are going too slow). Under some circumstances (the right car + correct road conditions) this can save fuel vs just maintaining a constant acceleration/speed.

FYI:
I don't do "engine off" coasting either. However, the main thing that "engine off" gives you (fuel wise) is a combination of the distance of a neutral coast with the fuel savings of a "in gear" coast.

i.e. your "coasting" options are:

1) In gear coast gives you no fuel usage (assuming you meet the requirements of your car for fuel cutoff), but you do have the engine/drivetrain drag lowering the distance you can coast. This may be a significant drag, or it may be very little (properly lubing up everything can make a HUGE difference in the drag here).

or 2) Coast in neutral, with the engine on. This one has the full coasting distance (although even there you can extend the distance by properly lubing up your wheels and/or improving your aerodynamics), but you pay fuel for "idle". How much fuel you pay, will depend upon a number of factors (including how much drag your car accessories put on your engine).

or 3) Engine off coasting gives you "the best of both worlds" FE wise, in that you have the full coasting distance/speed of neutral coasting, while also getting the full fuel savings of "in gear" coasting. However, engine off coasting is also more difficult to do correctly/safely, and in some places is technically illegal. Therefore some people would not want to do engine off coasting for safety/legality reasons, even though it is the best of the three options for FE.

Personally, I find myself normally using #1 (coasting in 5th gear), as the best current compromise for my needs. However, that's partly because I've greatly increased my "in gear" coasting distance from various lubrication that I've done. So at this point, I generally find I coast about 2/3 as far in 5th as I do in neutral (whereas in the past, before all much lube efforts, it was a much bigger coasting distance "penalty" to be in 5th). And since the 5th gear coasting is "free" (whereas the neutral coasting requires fuel for idle), it often just makes sense to stay "in gear", especially when I have to slow down anyway (such as when approaching a red light)...