Warm Start Fuel Saving Tip
 

Sometimes you don't realize the things you do to save fuel.... Often it takes someone else to point it out.

Thats what happened when Xcel stopped by for a visit last week. Via GH and private messaging, I gave him all of my tips so he would be ready for a test drive when he got here. He did quite well for several segments, until it was time to switch drivers. He pulled into a gas station, put it in park, and powered down... Noooooooooo I exclaimed!

The last time I had a reaction like that, my wife had accidently reset my MFD while wiping the pesky dust off of it. She told me that I looked like someone just shot my dog.

Anyway, I realized that I forgot to tell Wayne one of the basic rules that I have, don't power down unless you don't plan on powering back up again for awhile. I use 15 minutes as a guide. This is because for whatever reason, you take a substantial MPG hit while powering up, even if the ICE is nice and toasty. It seems that regardless of the ICE temp, some program automatically kicks in which runs the air/fuel mixture very rich for 30-60 sec. After that everything is back to normal, except that you could see 0.1 to 2 MPG shaved off of your average, depending on how far you are into the tank.

So when I am out running errands, I just keep her powered up as I bounce from Walmart to Pepboys to Home Depot, etc.... When I walk away, the car just beeps at me for awhile. When I get back in the car, the yellow light shaped like a key goes off and I proceed to the next stop.

It is my assumption that without the key near, no one can drive off with it, although I haven't actually checked. I live in a low crime area so I'm not too concerned about anyone stealing it, especially when it is parked in my garage. In my particular case, this works well for me. I would rather trade 1 or 2 bars on the battery icon for 1 to 2 MPG on the MFD.

I'm not encouraging anyone to actually do this. I'm just telling you what I do. Currently I have 896 miles on this tank and will be filling up on the way to work at just over 900 miles. I will also be trying out a radical new tank filling technique which will hopefully increase the capacity of the bladder/tank.

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

I need to understand this.

What is the difference between a reboot and a power down? Is it model sensitive? I have an HCH. I reboot all the time, and because I have a MT, I just slide it into gear to revive the ICE.

If I reboot and the computer program says to itself, "rich burn", am I losing the advantange of rebooting???

Please don't confusel me!!!

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

This is specific to Prius. From what I understand, the HCH guys reboot while moving. I don't have to do that because my ICE will shut down completely while gliding. Powering down in a Prius would only be done if you were stopped and planned on leaving the car.

Sorry for any confusion, thats why I posted in the Prius forum.

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Well, my limit for keeping the car powered is 5 min. I find that once the car has been sitting idle for a while, it will be running rich for the first minute anyway. It's a little worst than a full warm start but not by much, especially when the outside temperature is warm.

And I have a Canadian package A, i.e. no smart entry. When the car is powered up, the key fob is locked into the slot. I have to take the physical key out of the fob and lock the door from outside. I normally turn off my MFD when I get out that way, but the Canadian cars have daytime running lights which is a big giveaway. I just don't feel confortable leaving the car like that for too long.

But then again I'm not shooting for 900 mile tank... :D

Andy

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Thanks to Krousdb's fantastic mileage and a heads up from Xcel, I've started to use the Pulse and Glide technique. I've got no idea how well it is working because the tank already had a bunch of miles on it at low mpgs due to vacation style driving. The tank already had fast highway driving and a lot more in town driving on it than usual. Pulse and glide brought it up from 58 to 60 but regular driving might have done that anyway.

It sounds to me like the Prius goes into autostop when in neutral, is that correct? The only way I can get the ICE off in my HCH is to turn the key off to do a "manual autostop" or "reboot". It would be nice to mod it with a forced autostop button so a full reboot is not required. With a true autostop the car has PS the entire time and the gauges function all the time as does the radio. With a manual reboot you lose power steering for a few seconds, the dash resets (the car may not be keeping track of the miles drivin for a few seconds), and the radio cuts out on restart.

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

The Prius ICE shuts off whenever it possibly can, so when you take your foot off the accelerator, neutral, park, reverse all usually make the ICE shut off. It has certain warmup sequences that will keep the engine running in order to reach a certain temperature in the catalytic converters, but turning the car off and on will not avoid these so in general there's no need to reboot a Prius.

Sounds like the HCH really could use that mod, especially in Canada because of the daytime running lights, a reboot would cause them to turn off and on.

It shouldn't be that hard to do, all you need to find is a wire that stalls the motor when unplugged, then simply attach a normally closed pushbutton switch to that wire so that pushing the switch disconnects the wire temporarily.

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Hi krousdb,

I tried the "stop and go" vs. "stop, restart and go" you mentioned (out of curiosity, after xcel talked about it at the WI/IL hybrid event this weekend)... but I found no significant difference in the first 5-minute bar. See my results here:

https://www.greenhybrid.com/share/br...&imageuser=1607

Here is my full method:

1. Drive 15-20 minutes to make sure ICE is completely warm.
2. Stop and put in park (do not power off).
3. Wait until next 5-minute bar appears (this was ~2 minutes).
4. Drive a 10 minute loop. (See last 2 bars in first image. First bar of those is ~75 MPG.)
5. Stop, put in park, and this time power off. Wait ~2 minutes.
6. Power on, drive the exact same 10 minute loop (see second image - again, first bar is ~75 MPG).

So... what gives? :D Your post made it seem as though the first bar after the full power off would take a large hit (perhaps be below 50). Now I'm curious how much of a mileage hit it was for you and what method you used.

In terms of being able to do it (whether it is really needed or not), I have a 2005 with no smart key, and here's what I found:

- The fob is locked in the ignition for as long as the Prius is in any state except off.
- Using the backup fob I got from the dealer when I bought it, the Prius refused to lock from outside (when it was still in "ready" mode).
- Using the mechanical key, the Prius would lock from outside, and remain in "ready" mode (as accwai describes below).

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Locutus,
I have no test data to show you. I just know that by not powering down, I can move from store to store in a large strip mall without the ICE ever coming on. If I power down, the ICE comes on about 8 seconds after every restart and remains on for 30 - 60 sec depending on how long I was powered down. Of course, I will have to take a hit while driving home to charge the battery, but it will be less that starting the ICE several times.

I have noticed that when the ICE starts after a power up, the system draws much more power from the battery until the ICE has gone through it's warmup routine. I can see this with the voltmeter that I have which measures HV at the battery. Then the ICE takes over for propulsion and also recharges the ICE. Perhaps this is why the second bar dropped ~ 15 MPG during your second test.

Or.... there could be differences between our cars. Like I said, I have no concrete data to back it up. Your skepticism is understandable.

Thanks for the tip about using the key to lock the car... I never thought of that!

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Hmm... if you're picking up a larger draw with the voltmeter after startup, but not after "park and go" (no draw in your case - since you are able to do short hops with no ICE at all :)) there has to be something to this - whether it's uniform across all prius IIs is still up for debate.

What I saw was in both cases was I was able to do "pulse & glide" (and getting ICE to shut off) immediately, compared to at least 3 minutes after a cold start - suggesting the computer knew the ICE was already warm. But as for the second bar in my "park, restart and go" test... I can't attribute all of that to condition differences (after all, it was the exact same course, hit the lights about the same, about same speed and technique, etc).

I'd be very interested to see your results if you do it again.

Re: Cold Start vs Warm Start, Fuel Saving Tip
 

Well, there is probably more to it than just being able to pulse and glide. My experience is that once you leave the car idle in the power on state for a while, the first bar after you start again is always much higher than usual (Canadian cars uses L/100km on the display, higher bar means higher consumption rate). That is the case even when pulse and glide is fully enabled. My interpretation is that the car is burning rich after the idle, to bring the catalytic converter back to temperature perhaps. I think this rich burn is much more of a drain than the initial burn during a warm start. And it happens regardless of a power down or not.

As for Dan's strip mall hopping, the rich burn after idle doesn't affect him multiple times as he is running EV. So keeping the car powered would make sense. But here in Canada, there is no strip mall big enough to require hopping like that. I would claim that the difference between powering and shutting down is quite minor if you just park the car once, go walk around in the mall, and then go home right away.

Andy