--- MPG Gain With Engine off at Stoplights? ---

[NeilBlanchard]

Hiya,

I have been doing this more often now, especially if I can see the lights in the other direction change to yellow (if I am at the head of the line); or I wait until the vehicle 2 or 3 ahead of me starts to move, and then I start it up again.

I look at it more from the stand point that it doesn't hurt my FE, that I have worked so hard to maintain.

Another thing I have started doing is pulsing at the top of a hill to start my glide at a higher speed. If you do this right, it gains more than it loses.

[Formula413]

Originally Posted by bhazard

One thing I wonder about shutting the engine off is... does the computer go into open loop or does it run a little rich on startup? Or is that only on a cold start.

I could double check with the scangauge but I'm pretty sure if it is warm it would stay in closed loop.

To the original question, regardless of the savings, why wouldn't you shut the engine off when it is not needed? I always kill it at red lights, try to watch the opposite light to see when my green is coming, and on lights I hit all the time I even count off in my head how long they take to change so I can fire it up with just a second or two to spare. Hardly too much effort to make on behalf of the planet and my wallet.

[basslover911]

Well all I wonder is starter wear... because on a typical city drive I could turn off my car probably 10 times instead of just once (when I first turn on the car)...

[dcb]

re: starter, I think DAOX responded to this question in another thread, but IIRC the most notorious hypermiler using an automatic got 80,000 out of his starter.

Folks are spending hundreds per year idling, that will likely go up.

A starter for your 07 car is less than $200 from autozone. A starter for my car is $75, without any shopping around. My annual fuel costs for idling are somewhere around $150.

So if in my scenario, I would have to replace starters twice a year to lose money on the deal. My starter should last 16 years, since I bump start half the time.

The break even point is somewhere around a year on average for parts if I had to guess. Labor costs is at your discretion, at it's essence it is removing two bolts and two terminals, though some starters ARE a pain to get to. I don't mean the "I don't feel like getting my hands dirty" pain, but like you have to take off the intake manifold pain. Ah well, just more bolts

[PaleMelanesian]

I believe it was closer to 95,000 miles that Wayne got on his starter.

My civic goes to Closed Loop immediately, within one update cycle. That's with the scangauge set on Fast refresh, too.

[ptsmith24]

Originally Posted by Formula413

I could double check with the scangauge but I'm pretty sure if it is warm it would stay in closed loop.

To the original question, regardless of the savings, why wouldn't you shut the engine off when it is not needed? I always kill it at red lights, try to watch the opposite light to see when my green is coming, and on lights I hit all the time I even count off in my head how long they take to change so I can fire it up with just a second or two to spare. Hardly too much effort to make on behalf of the planet and my wallet.

Yea, I hear ya. I like being at least a few cars back from the light. Although I can't see the light going the other way, I have time to start and move before the traffic ahead of me moves.

[randerson0248]

Do you think that the additional alternator load on recharge of the battery after restart will negate the fuel saved while the engine is shut off?

[PaleMelanesian]

No. I see a 20% or more gain by shutting it off at stops. The alternator load is minimal compared to fuel used for idling.

[Formula413]

Just an update re: open/closed loop. I checked today and sure enough it stays in open loop for about 15-20 seconds after startup even when warm. I'm still inclined to think that the increased fuel burned in that period due to open loop is less then the fuel saved by not idling at the light. This would be very hard to quantify though.

[ptsmith24]

Originally Posted by Formula413

Just an update re: open/closed loop. I checked today and sure enough it stays in open loop for about 15-20 seconds after startup even when warm. I'm still inclined to think that the increased fuel burned in that period due to open loop is less then the fuel saved by not idling at the light. This would be very hard to quantify though.

But, if I understand your post correctly, that would depend on how long you would be idling...I think. I usually turn my motor off if I know I'm going to be sitting for longer than 30 seconds. Less than that, I just idle. Once I get the 'guino calibrated, I'll have to try and get some semi-exact numbers to back up the theory.