Sitting at idle or turn off engine?

[cat0020]

Originally Posted by R.I.D.E.

Your objective is to arrive at the light after it has changed and traffic starts moving. DFCO is the same (as far as fuel use is concerned) as turning off the engine and restarting it when you cruise through the intersection without stopping at all.

This works with manual transmissions, but no where near as well with automatics.

regards
gary

My 1989 Toyota Camry with auto transmission could be put into N while the vehicle is coasting downhill or to a stoplight, then shift back into D when the light turns or the gradien of the road flattens out. The shifting could be done while vehicle is still in motion, sometime at highway speed.. hardly noticing the transmission shifting when I put it back into D.
I did the same thing on my previous 1992 Mazda 323 hatchback, shifting is not as smooth, but caused no problem to the transmission whatsoever.

[theholycow]

Originally Posted by cat0020

My 1989 Toyota Camry with auto transmission could be put into N while the vehicle is coasting downhill or to a stoplight, then shift back into D when the light turns or the gradien of the road flattens out.

Gary was talking about DFCO (Deceleration Fuel Cut Off), which requires you to leave it in gear. While "coasting" in gear (actually engine braking), depending on the specific car and circumstances, the computer may shut off the fuel entirely and let the road keep turning the engine. If you intend to slow/stop, DFCO is more efficient than neutral. If not, you generally lose more energy (in the form of lost speed) than you spend (in gas) idling the engine in neutral, based on my experiments and experience.

[palemelanesian]

Originally Posted by theholycow

If you intend to slow/stop, DFCO is more efficient than neutral. If not, you generally lose more energy (in the form of lost speed) than you spend (in gas) idling the engine in neutral, based on my experiments and experience.

I agree completely.

[thornburg]

Originally Posted by PaleMelanesian

My "normal" engine goes into closed loop within a second after restarting.

Sorry for the OT question, but could someone explain "open loop" and "closed loop" to me?

Thanks in advance.

[R.I.D.E.]

I used to never downshift to slow down, just coasting and brakes.

I can't quantify the difference in mileage, but my mileage (and this is specific to the VX) improved when I stopped P&G at anything over 45 MPH, and shifted my focus to maximising DFCO. Most of the drivers around you will get impatient and pass you just so they can use more brakes to stop for the light.

My best day is when I can drive 40 miles through more than 40 lights and not spend more than a minute TOTAL time sitting at lights in close to an hour of driving. I do cut my engine off when I am coasting the last .3 mile to my house. My driveway is at the bottom of a swale and I go past the driveway up the hill, and let gravity back it up to the driveway. Once I get to the driveway its a 12 foot drop in 80 feet. I coast down the slope backwards into the garage.

regards
gary

[R.I.D.E.]

Closed loop is when your fuel injection system is reading the oxygen sensor and continuously readjusting the mixture.

Open loop is when the computer just feeds a specific (usually richer) mixture to the engine becasue the feedback system is not working at that time.

Wide open throttle and cold starts are times when most engines used closed loop.

regards
gary

[WhitePolarBear]

My rule of thumb of turning off engine at drive through:

1. McDonald - idle but put to Neutral.
2. Jac in a box - turn off your engine.

[palemelanesian]

My rule of thumb:
Don't drive through. Park and walk inside. You'll use less gas still, and often get the food sooner as well.

One more thing:
UPS has a policy (3 years running now), that their drivers shut off the trucks if they stop, including at red lights. I'm sure they've done their homework about the gas savings vs starter maintenance.

[trautotuning]

Originally Posted by PaleMelanesian

One more thing:
UPS has a policy (3 years running now), that their drivers shut off the trucks if they stop, including at red lights. I'm sure they've done their homework about the gas savings vs starter maintenance.

Really??!?!

I bet they have... such a big company has to account for engine wear life and replacement of parts vs the cost of gas while idling.

I always turn it off when sitting in the car for more than 30 sec, but never at stop lights. Ex. waiting for a friend outside their house, waiting for my order at sonic, stuck at a railroad intersection, etc.

Also, I never turn it off (even if I am sitting and waiting to get my #4 at sonic) unless the engine has reached full operating temp.

[SolidLiquidSnake]

I have started to turn my car off a little more now... I dunno if I'm seeing a real improvement but this thread has persuaded me to try it and I now try and turn off engine when a light up ahead that I know is long just turns red and I coast up to it and wait and start it up when it's green, I think that the rule was waiting 10 secs or longer turn it off but I think it's more like 20 honestly. Is this rule even factual? Be nice to know about my specific car and how much gas is used on a warm start.