Engine Temps - Coasting To a Stop
 

Question for the hypermilers. I've been killing my engine as I coast to a stop when I approach a red light (was that a run on sentence?). Do you wait for your engine to warm up before doing this? Or start doing this immediatly?

I personally wait for it to warm up as I suspect that there's a warm up enrichment program and don't need to dump that extra fuel on start up. I was just curious if anyone had some insight on this :)

I wait for it to warm up because I do not want to delay the car from reaching a point where its emissions become the least. If you P&G all the way and never warm the car up you are probably having horrible emissions.

I bet the emissions of multiple cold starts are horrible, and it causes a lot of extra engine wear. Supposedly 90 percent of engine wear occurs during cold starts. So I wait at least a few minutes after the coolant is up to temp. Just because the coolant is up to temp doesnt mean the oil is.

yeah i wait so that the engine is warm because cold starts use a ton of gas

That would be interesting to see data on. I think I remember Dan saying that he was engine off over 50% on his commute. So what would the emissions be for that time that the engine off compared to on. At least here my exhaust temps close loop pretty fast usually by 100 yards. Once you're in closed loop is that's all thats required for emissions or is there more to it? Operational temps will give better FE(although the top 10 list is tons of engine off) but on the emissions what is required?

It is about heating the cat up for emissions, not really getting to closed loop. I am not sure how long it takes, though.

I don't know the EPA list cars and the amount of CHG in tons/year when you check the EPA figures. So if you drop the MPG figure by 30-40 % or more then doesn't it stand to reason that the total sum would be better, not necessarily equal, 30-40% might translate into 25-30% but still better. Less fuel has got to be better all the way around with todays modern engines. Just my thoughts I would be interested to here other views.

As far as multiple starts the first one is the only one that is done without previous oil circulation so the remaining ones would not be a problems. If it's a manual transmission you can bumps start. Even if you used the starter when was the last time you replaced one. I've had several cars with over 150k and never replaced a starter.

It is listing, primarily, I think, c02 emissions, and not things like sulfurs and nitrogen oxides. But then again, I am not sure of. However, I do believe that a car does more than 30-40% of it's polluting during the warm up phase of a medium sized trip, so that extending that polluting phase to cut fuel use by 30-40% would not have a net benefit.

My engine often doesn't even reach it's full operating temperature by the time I get to my destination when it's particularly chilly outside, so I normally EOC right away. My mpg on the SG drops like a stone when the engine is running at a stop.

The only time I leave the engine running 100% of the time is when it's REALLY cold out. Like when I NEED the heater to clear the frost from the inside of the windows. During those times, my FE drops dramatically. I should just install a fireplace with a chimney in my car when it's winter time. Can anyone say emissions? :p

I also have a general question for GS members: Why does the heat in my car turn cold when the engine is off? The vent still blows, but no heat. Surely the engine block is still hot when it's no running. Is there a way to make the air stay warm?

your heater core is like a small radiator. when you shut down the engine the coolant isn't moving anymore

But the stationary coolant is still hot right? I can't think that the coolant would get cold immediately.

My car is so old, it doesn't have a catalytic convertor :).

I use P&G on my way in (although have the water at 80 degrees C from the block heater on one of the journeys). I use 50% throttle, then cut the engine. I use less petrol, therefore less CO2 is produced, and my engine isn't in the warm-up phase. The engine warms up more quickly at 50% throttle for short periods compared to constant low-throttle driving.

Peakster - the air is heated by the engine coolant, which goes through pipes into a little radiator under the dashboard. The engine coolant is pumped by the water pump, which only works when the engine is running. So when the engine is off, you are using the heat in the water in that little radiator, which cools down quite quickly.

Do you have a grille block by the way? If not, it is a good way to get the car to warm up faster, especially when using P&G.

Edit - two posts since I started writing this :). Still some useful info though.

Yeah, I do have a grille block (see garage pictures), but I need to fabricate a better-sealing one. I wonder if I could change my water pump so it works when the key is in the "on" position when the engine is turned off?

If it is not too cool out then you probably should shut it off since you are burning gas at a high rate and going no where. This also give the heat that you already generated to spread into the colder ports of the engine a little more gradual. What kills me is the light at the end of the first block that I sit at while burning .5gph warming up all the time.

I would think it wouldn't get cold immediately..

Yeah, but he's talking a level of cold that you and I never see...

That's EXACTLY what I was thinking... I mean, 70-200F in a few minutes is quite a bit of stress for aluminum :P

But, as said in the first reply -- emissions are a concern too - waiting for the catalyst to heat up.... I think I'll split the difference and let my engine warm up 1/2-3/4 before shut down. We'll see what the meter says in a few weeks :P

As for the 90% of engine wear comes from start up.... I think a lot of engine wear comes from cold and dry start up, but 90% seems a bit high.

Thanks for all the response :D

Heating Up
 

I've noticed that cutting the engine and coasting will actually heat up the coolant temp while the coolant sits in the block jackets, unpumped. Didn't think about the Cat...

This is a good thread...

For emissions purposes, there's no way to know the Cat temp -- just coolant, IAT, or other parameters if equipped (oil temp).

I know some that P&G on warmup -- I guess it helps FE, not emissions. With the recent cold-snap here, I'll try the engine-on coast for warmup.

So, for the minority of us automatics, do we leave it in "D" to heat-up the transmission, or pop to "N"? The transmission needs heat too...

I don't have the answer - but that reminds me of another scenario -- Engine off - in gear coasting... Until today, I was doing this if I burned too long and there was a stop coming up... But earlier today I had an epiphany that doing so was just cooling down the exhaust/emissions equipment with cool air :/

Does anyone know if the programmers fully cut back on fuel when coasting (0% throttle, in gear cost down)? Or do they add a little fuel to keep emissions equipment warm and ready to go?

Engine braking = complete fuel cut.

If that is the case, why does my scangauge still read ~0.3 GPH when I do engine braking?

Peakster -

I see similar behavior on my ScanGauge. What I read on saturnfans.com is that for my drivetrain, fuel does not completely cutoff. It goes down and down, closer to 0, *but*, then the RPM gets to the "idle RPM", the fuel is restored, because the ECU/PCM never wants to go below the idle RPM. Here is where I read it :

Negative Fuel Trim...Constant
https://www.saturnfans.com/forums/showthread.php?t=89959
Other drivetrains are much better at this and can be very thrifty about cutting fuel when the right combination of driving events appear to the ECU/PCM, i.e. a certain combination of "0 throttle + in gear + brakes applied".

CarloSW2

Pulse and Glide while the cat is still cold would produce much more NOx and SO2, but less CO2 cause less fuel would be burned. I think the cat has to get to something like 600 deg F, before it is fully functional. I would think that in the winter (at least in VT) the cat would be doing nothing if you frequently EOC. As far as engine wear, it is hard to know...I dont know if anyone has been EOCing for over 150K. I think in warmer places, EOCing sooner after startup makes more sense.

Here's what I know for sure:

Every modern EFI car utilizes a fuel enrichment map that is based upon coolant temperature, as well as one that is based upon air temperature. At what portion of the mapping the ECU operates has little to do with closed loop operation except that open loop is the designers best guess based upon all other sensor data sans the oxygen sensor - which may or may not be much less efficient. What it boils down to is that the coolant temperature enrichment map is a simple curve. The warmer the engine can safely operate, the less the temperature map will enrich the basic injector mapping. Because of this, an engine block heater will absolutely improve fuel economy - even in the summer time.

As for fuel cutoff under engine braking, it is typically rpm dependent. My bet is that this minimum limit is likely programmed using a combination of what re-engages the engine smoothly and or keeps it from outright stalling when one engages the clutch. (The momentum of the coastdown rpm should be enough to kick the motor back on instantaneously when the clutch switch is tripped.)

Anybody with a programmable ECU can play with these things for some interesting results, but it's unlikely one would gain any real economy vs. stock by doing this.

The 'cold startup engine wear' is oil industry hype to get you to buy their oil. If you are running the proper oil weight for your climate, it's not an issue to be concerned with. Drainback of the oil is the primary cause of this cold start wear - which really has little to do with temperature. Once you have the motor turning that first time of the trip, the brief interludes of EOC are not going to be long enough for complete drainback of the lubrication system, so all of the important parts are already lubricated for the next bump start.

I can agree to that :) I've seen people tear apart the engine that was in my last car after 250K miles -- the factory hatching was still visible in the cylinders :P

When I'm in 5th -- I can feel the engine re-engage when I get down to around 1500rpm. I assume it's because there's very little gear lash in my 5th, so when the engine does come back to life, it kinda taps the driven gear :P

starter
 

> Even if you used the starter when was the last time you replaced one.

It depends greatly on how good a starter the car had to begin with (unfortunately I've had to deal with crappy Lucas starters), and the treatment it got. Cranking when the battery is low is the worst thing you can do to a starter. Some cars or starters have circuitry that won't allow it. But if yours does allow it, and on starting you hear that super slo mo groan from the engine and possibly even a buzzing noise rather like the hum from high voltage power lines coming from the vicinity of the starter because the battery is below 10 volts, STOP! Push start, or get the battery charged, unless you like replacing starters. Starters have even exploded when subjected to that kind of abuse.

Replacing starters too many times has made me hesitant about shutting of the engine in situations where I'll have to use the starter to start up again.

I use my starter dozens of times per day in my Geo and it's still working just as well as when I bought the car August 2006... actually it's really the ONLY thing that's working well. The motor mounts are starting to creak under load and theres lots of 'interesting' noises coming from virtually any moving part in the car. But whatever, @ 250K, it still moves forward/backward, steers left/right, and that's what's most important to me (that and getting 50mpg+ tanks).

I've replaced the starter in my Fiero at least twice for the 55,000kms I drove it (no hypermiling techniques at all) and even with the added stress of EOCing & FASing, 34,000kms later, I have yet to replace one in my Geo.

I EOC right from the get go. I want to get to the hwy with the least amount of engine on as possible. Once at the hwy the engine can run in a more even low load state and warm on up as I ease out of town.

psy

Depends on engine speed, and coolant temperature iirc. If the car is below some rpm, it automagically "idles". This rpm depends on coolant temperature. :p

I didnt feel like saying all that. If the car it in gear, 0 throttle, at 1000 rpms there will be no fuel cut, and therefore no engine braking. Only when engine braking (as defined by the engine no longer igniting gasoline and using the friction of pumping air to slow the car down) is happening will you have a fuel cut.

Just because there's a little fuel being injected, doesn't mean that engine braking doesn't occur. As long as the engine is robbing power, instead of providing what's needed at that speed, provided the transmission is in gear, then engine braking occurs. For instance, lets say I'm in fifth, and pass the idle cut while decelerating. There's a small amount of fuel being injected, but because of the pumping losses inherent to gasoline engines, the compression stroke, where pumping losses occur, are what's slowing down the car on the engine side (i.e. by putting it in N, I can avoid engine braking and slow at a lower rate). At least that's how I've always seen it. Not trying to troll or anything, just get terms straightened out and whatnot.

Another nice example imo are diesels. Since there aren't pumping losses of the same magnitude compared to gassers, the force provided by engine braking isn't much at all. So, for big diesels, a separate system is needed to take advantage of engine braking. There's also the closed throttle definition, but this applies as well, since imle, most cars use a separate pathway for idle air flow. :thumbup: