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Old 02-22-2012, 09:35 PM   #1 (permalink)
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A few questions Coasting,Overdrive button,Air intake

I have a 2000 Mazda 626 LX

Is it safe to coast with an automatic car? or this only applies to standard cars? Is it safe to put my car in neutral down a hill then put it in drive?

What exactly is the overdrive button for? Should I be using overdrive for around town like I have heard?

Also do those air intakes like injen and akimoto/Conical air filter systems safe on gas?

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Old 02-22-2012, 09:41 PM   #2 (permalink)
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you're fine to coast in neutral but i would leave the engine running. i leave my car in overdrive all the time, no matter what kind of driving i'm doing
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Old 02-22-2012, 10:03 PM   #3 (permalink)
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Yeah I leave it running but decided today to start doing this. I wasn't sure if I would ruin the transmission so I had to ask.

I plan on getting the scangauge E in 2 weeks. All last week I was using Cruise Control and have already seen a difference with how often I need to get gas.
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Old 02-22-2012, 10:17 PM   #4 (permalink)
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Some auto tranny cars benefit from neutral coasting some don't. My 2 gm's coast almost exactly the same drive or neutral. My dodge doesn't it actually downshift during coasting and engine brakes. It goes really smooth N-D above 40, below that speed not so smooth. If it goes smooth N-D I can't see how it can hurt anything. But if it doesn't help your coast it's a wasted effort and possible wear & tear.

I'd always leave OD engaged unless driving a lower speed hilly road where it's downshifting every hill.

Cold air intakes, high flow intakes, basically only change peak-maximum power. Regardless of how easy the air gets thru the filter, the throttle plates restricts airflow down to match what the engine needs to do the task asked of it. If throttle is wide open then intake/filter restriction, cold air denser etc... can make a difference. 1/2 a percent of the time we drive.
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Old 02-22-2012, 10:48 PM   #5 (permalink)
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I would think short hills would be fine coasting, but 2-3 miles down some mountain?;
don't think so w auto.
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Old 02-23-2012, 03:44 AM   #6 (permalink)
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Neutral coasting engine on is no problem. The tranny parts get lubed as long as the engine is on, even if you coast 25 miles.
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Old 02-23-2012, 11:10 AM   #7 (permalink)
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Check your manual. If it says that flat-towing is permitted (aka dinghy-towing), then you can coast in neutral without damaging your tranny or shortening its life. If it recommends not shifting to neutral above 35 mph, then follow that recommendation.

Just because you can coast in neutral with the engine running, does not mean you should. Modern engines cut off the fuel to the the cylinders when coasting (DFCO), so shifting to neutral would actually use more fuel than if you left it in gear, unless the engine braking is enough to force you to use throttle to maintain speed. Shutting off the engine while in neutral will indeed save gas, but is controversial due to safety considerations. YMMV.
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Old 02-23-2012, 01:11 PM   #8 (permalink)
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Quote:
Originally Posted by reb01501 View Post
Just because you can coast in neutral with the engine running, does not mean you should. Modern engines cut off the fuel to the the cylinders when coasting (DFCO)
Sure, but then you're braking (=wasting energy).

Quote:
so shifting to neutral would actually use more fuel than if you left it in gear, unless the engine braking is enough to force you to use throttle to maintain speed.
In the end, you'll use less fuel - even though the engine is idling and using fuel to do so.
The difference is in the braking (DFCO / engine braking) - or not braking (coasting).
You'll coast far further than when letting go of the throttle and go into DFCO.
That's where the gain is.

(If not, the tranny has some kind of freewheel in it that automatically lets you coast.)

Coasting has become my main way of reducing speed - whereas I used to use DFCO all the time, it's now my second means of slowing down, with braking only coming third.

Quote:
Shutting off the engine while in neutral will indeed save gas, but is controversial due to safety considerations.
You loose powersteering and (after a few dabs at the brakes) power brakes. That's my main reason not to shut off the engine.
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Old 02-23-2012, 01:58 PM   #9 (permalink)
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Quote:
Originally Posted by euromodder View Post
Sure, but then you're braking (=wasting energy).


In the end, you'll use less fuel - even though the engine is idling and using fuel to do so.
I can't test this with my auto, but I assume you have. The steepness of the downgrade would certainly be a factor.
Quote:
The difference is in the braking (DFCO / engine braking) - or not braking (coasting).
You'll coast far further than when letting go of the throttle and go into DFCO.
That's where the gain is.

(If not, the tranny has some kind of freewheel in it that automatically lets you coast.)

Coasting has become my main way of reducing speed
Huh? I was following you until this point. If by "coasting" you mean "shifting to neutral", isn't this a contradiction? How does shifting to neutral allow one to reduce speed? Oh! You mean via air resistance and road friction? OK, now I get you. But on a steep hill, you might need the DFCO/braking to avoid usafe speeds. I agree that the brake should be the last resort.

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