Help me understand EOC (engine off coasting)
 

Hi!

Haven't been active here, been busy busy.

Did do some "mods" to my car though. Hit a deer early Thanksgiving morning, broke a headlight and crumpled my hood, lost my grill. Insurance considered it totaled so i had to fix it myself.

So I replaced my headlights with brand new ones, switched to all LED's inside and out, uncrumpled the hood to the best of my ability, did a full tune up, did some gap sealing around the outside with gask maker, cleaned my crank case and created a grill block out of LED light bars haha.

But I saw only negligible gains. I'm still in that 23-24 mpg area.

So I've started playing with EOC while I save up for some more aero mods.

I have a manual, but I'm not really sure how it works- when I leave it in gear and turn the key off, I have full control on brakes and steering (necessary, I live in a hilly, windy roads place) but I'm concerned it's just pulling in unused gas on revolutions. Is this the case?

It's also nice because I just turn the key and it jumps right back to life, smooth as peanut butter.

In neutral I lose brakes and steering, which can be kinda terrifying. But I've noticed I can just put it back in 5th gear after turning the car back on, even as low as 15 mph, and it'll turn on no problem.

Thing is, neutral EOC really only works for one stretch in my town.

The other issue is that when I turn my car key off, my headlights go with it, so I can only EOC during the day.

Would an ignition kill switch cure this issue?

Or should I look into fuel injector kill switches? They seem sorta complicated though...

The car automatically cuts fuel when you leave it in gear and coast, even with it "on". Your momentum turns the engine even though no fuel is being injected, and the accessories such as the power steering and brake booster keep power. This is called Deceleration Fuel Cut Off (DFCO). Some of your momentum is lost to spin the engine and accessories.

When you put the car in neutral (or better yet just put in the clutch) and turn the engine off, that is Engine Off Coast (EOC), and is the most efficient way to coast unless you actually need to slow down, in which case DFCO is the best method.

When you EOC, you don't need to have the key in the off position the whole time, and that can be a bit dangerous because if you turn it off to far, the steering wheel could lock when you go to turn. Simply turn it off long enough to kill the engine, then click it back to the on position, and when you're ready for the engine to come back on, let the clutch out while in 5th gear to bump-start the engine. No fuel will be injected until you bump the engine back to life.

The Outback is a bit of a pig and extremely difficult to mod for much better fuel economy.

There's a few older threads on here where members failed to achieve the MPG goals they were aiming for. Zerohour documents his efforts here:

https://ecomodder.com/forum/showthre...-5l-14034.html

Another member, Brucey, had an Outback of your vintage and has a few threads on various mods he tested. Do a search for threads by him if you're interested.

So if there's danger in putting it in neutral and coasting, why not leave it in gear and coast instead, beyond engine braking slowing you down a bit? I just turn it back to acc and the only things that I notice are the odometer quits and my headlights turn off.

What's a way around that happening?

And I'm really only aiming for about 28. I don't have any delusions about this car getting amazing mileage. I drive it because it's a tank. Deer heavy area. I have a close call probably 3x a week in my 50 hour work schedule.

I'd rather survive in this than be buried in a metro.

Post here before buying stuff.

I'm not sure you're understanding the difference between DFCO and EOC. There's no advantage to turning the engine off if you are DFCO (leaving it in gear and letting momentum turn the engine). The engine already cuts fuel entirely when doing this, even when it's "on".

As I said, the 2 strategies have different purposes. EOC is useful for maximizing fuel economy when you don't want to slow down. DFCO is useful for maximizing fuel economy when you do want to slow down. EOC doesn't power the accessories on your car such as power steering and brakes, which is why it's more efficient. It's not trading vehicle speed to power these things (and spin the motor needlessly). DFCO robs the vehicle speed in return for providing power to accessories.

The way I would use EOC is if there was a long downhill section that allows me to coast near to the speed I want to travel. I'd turn the key to ACC, which would kill the engine, then I would switch it back to run (not start). That way when I do finally want the engine to start, I just let out the clutch.

DFCO happens any time you're completely off the throttle and the engine is still turning, and you're slowing down. I use that all the time, anytime I need to slow down or stop.

I'm not saying you've got a bad vehicle, and my favorite car I've owned yet was a 1996 Legacy 5-speed manual. Best I ever averaged was 28 MPG, and that was with a 2.2L engine and lower chassis. I'm saying you'll have a very difficult time getting to that average considering the larger engine and greater frontal area.

Summary:

EOC (Engine Off Coast)- Used for minimizing momentum loss while coasting. Does not provide accessory power.

DFCO (Deceleration Fuel Cut Off)- Used when slowing is desirable, or losing accessory power is not acceptable.

Engine-off coasting is when you put it in neutral and then shut the engine off. This is the most efficient way to cover distance. If you leave it in gear instead, the friction and drag of spinning the engine slows you down - basically like riding the brakes.

As redpoint says, it's not necessary to key-off if you're just going to leave it in gear. By taking your foot off the pedal while in gear you're doing what's called "engine braking", which means you're intentionally slowing your car down by using the engine as a large friction brake. This also uses no fuel but robs you of momentum, so you only want to do it if you're actually trying to slow down.

The headlights are on a switched 12V source? Is this a Subaru thing?

The headlights turn off with the ignition, yes. Unfortunate, but how Subaru designed the lights. I'm in the same boat where I have to EOC cautiously or with just my parking lights on. The only lights that can stay on when the ignition is off are the parking lights. They have a dedicated hardware switch typically on the top of the steering column. I learned that soon after I bought my first Subie.

Shutting the ignition off while in gear is a good way to flood and damage it.

I never coast in gear unless I'm coming to a stop and I haven't timed my coasting properly.

Anytime I coast my engine is off if it is daytime and my 12V charge is at least 12V.

Nighttime driving drains the 12V too much.

I use the key because I'm too lazy to install an injector kill switch.

California98Civic installed an extra vacuum for engine off coasting.

LED lighting will reduce electrical load and allow you to engine off coast for longer periods without draining your 12V battery as much.

You don't want the key off the entire time the car is coasting, only long enough to kill the engine. Turn the ignition back to run once the engine has died. It will stay off until the clutch is let out or the starter is used.

My point is, your headlights probably only need to be off for 2 seconds tops.

Engine kill switch is the correct way to do this if you expect to EOC frequently. That would leave headlights on since the ignition isn't switched off.

If you can just turn off the key to do this, why do people install engine cutoff switches? It seems like a lot of work when you can just turn your key.
I recall asking before but this is only possible with manual transmissions right?

Try coasting first - with engine on that is.
Put the gear in neutral, and just let it roll
You'll be amazed how far it can roll
Yes, it'll use some fuel, but you get a whole lot further than with engine braking.

Get a hang for how far it'll roll from your usual steady speeds, and use coasting from a lot further out instead of engine braking


Only accelerate up to the speed you need to reach the next turn / stop / lights / crescent of the road / top of a bridge / ... at a normal speed for this conversion point, then coast towards it, accelerate again and coast to the next point.

You're a delivery guy, this works well in town or suburbs


The idle fuel use makes coasting with engine on not really worth it under about 15-10 mph .


Downhill, if not too steep you can coast engine on in neutral, or put it in gear and use engine braking if it starts building too much speed (uses 0 fuel)


A combination of engine on coasting and engine braking when you need to stop, can improve your fuel economy a lot.


Turning the engine off after the acceleration phase, is the next level in coasting.

It is possible to engine off coast in an automatic or CVT, but it is presumably bad for the transmission.

In the Civic I used to have I never did any engine off coasting above 10 MPH for any distance further than 100 feet (i.e., parking lot, driveway).

Or just buy an hybrid and let the computer do it all for you.

I had to add my 2 cents worth.

My big bad old 2000 Mercury Grand marques was able to get 28/30 MPG at 65MPH.

This was at about 2 GAL per hour. (Via Scan Gauge II)

At idle it ONLY used .45GAL per hour. IF I could get a car that used that little fuel driving it would be getting 100MPG+.

SO killing your engine is a waste of time and dangerous. Leave it running at idle out of gear; you can then simply put it back in gear when you need it.

This keeps everything working, power brakes, power steering, A/C, all gauges and lights, and there is much less drain on the battery as even an idling engine can be charging the battery, and IF you drain your battery coasting with the motor off you then pay for a heavy charging load recharging it.

The one problem with this is some car and trucks seem to have a odd thing happen, IE my Mercury and 03 Crown Vic will maintain engine RPMS at or higher that the RPMS needed at speed. Yet my 1993 Chevy Van and my 2002 Ford Explorer will drop to idle when shifted out of gear.

So unless someone can figure a way to get these cars that will not drop to idle to drop to idle, this will not work as good as it will on cars and truck that do drop to idle out of gear.

As I have not considered using this I cannot say how many GPH it was using out of gear and still revving to RPMS, could still be much less GPH as the engine is free spinning and NOT under any load out of gear.

Rich

The merc and crown vic could have lock up torque converters which could be unlocked. Been my experiences that Ford likes to downshift some trannies out of overdrive for any excuse hence with a locking tq the engine up rev.

In my Insight, idle is ~0.19 gallons per hour. I already get 100mpg cruising at steady speed. EoC helps further, but the better your gearing is, the smaller the gains from EoC. A vehicle geared such that it's at 90-100% load at your cruising speed would probably have almost no gains from EoC, aside from those from running at the RPM of peak BSFC. Might be another 5-10%? Anyway a good, modern CVT would probably see almost no returns from EoC, whereas a sports car with very short manual gearing would have a ton to gain from it. My previous Honda would cruise at ~4300rpm at ~65mph. Steady-state driving it delivered anywhere from 27 to 35mpg. With EoC I was able to break 50mpg on flat terrain a few times.

Dangerous though? Maybe in some cars. My car weighs in at ~1700lbs right now and stops fine even when the vacuum booster is empty for the brakes. It also steers fine without the electric power steering active... but the EPS actually stays active when the engine is off, so it's doubly a non-issue. My car is just about to turn 20 years old, and most new vehicles have electric power steering now.

I have seen what I would call a 1/2 downshift, the torque convertor unlocks and the engine spins up about 400/500RPMS, if that is not enough then she drops out of overdrive.

And again T double checked, my 2002 Ford Explorer does not hold RPMS coasting out of gear but drops to idle nicely.

Rich

Agreed. I just don't like flashing my lights at oncoming traffic. If I switch over to all LED including headlights, I might change the power source of the headlights. If I feel ambitious.