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Old 08-20-2012, 09:33 PM   #21 (permalink)
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Neutral coast is always better yes. Well if you don't know if your Automatic transmission will take the abuse don't be the first to find out. Do some research on your car beforehand like Rooster says.

Unless i drive on the highway or speeds 56mph and above i never use cruise control. I find you can either accelerate or let off the gas and coast a little in the eddies of the road. Like -.5% grade over a tenth of a mile. And in my driving i vary speed alot over little hills and such.

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Old 08-20-2012, 10:15 PM   #22 (permalink)
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It varies so much between cars, so neutral coast isn't always best or better.

My 2 GM's auto's don't care N or OD they coast the same.

I do know and after 100,000 mile the Stratus doesn't mind N coasting, it can be bumped into N under load and doesn't care. IMO if it goes out easy(out of drive) and in easy all's good and working for me(disclaimer) it's your car make up your own mind.

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Old 08-21-2012, 11:17 AM   #23 (permalink)
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Good reminder that he's driving a GM. It's programmed to essentially go into N on its own when you let off the gas. I'd just leave it in D.

"Your mileage may vary" applies to ... just about everything.
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Old 08-22-2012, 02:45 PM   #24 (permalink)
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I tried P&G from 60mph to 50 mph, the downside is that the transmission shifts down when i reach 50mph so on the way back to 60mph the engine revs at about 2500 rpm and upshifts again.

I don't know if it is worth it or im burning more fuel this way.
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Old 08-22-2012, 03:35 PM   #25 (permalink)
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I'm surprised, you do a comparaison of a constant speed of 60 mph to P&G between 50 to 60mph.

A basic mathematic say that the average with P&G is about 55 mph. So try P&G from 50 to 60 mph, then try the constant speed of 55 mph.

P&G is only working well with hybrids vehicules. It can also be useful in city when you drive without brakes between 2 crossroads. Glide is really usefull in many situations.

But on a long straigh line, with the same average speed than constant speed, the P&G is often worst (except with hybrids car, when the electric engine do the main work and the fuel engine work in her most efficient range).
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Old 08-22-2012, 03:38 PM   #26 (permalink)
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I forgot : P&G can be more efficient than constant speed at very slow speed, on the 1st and 2nd gear, and sometimes on the 3rd gear (up to the car).
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Old 08-22-2012, 04:02 PM   #27 (permalink)
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Quote:
Originally Posted by roosterk0031 View Post
But my 2 GM auto's coast same OD or Neutral,
Then you apparently have some freewheeling arrangement in the tranny when in OD.
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Old 08-22-2012, 07:43 PM   #28 (permalink)
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Echoing others, you'll need a UG or SC to know for sure but I can't tell you how it is with my Honda.

According to my Ultragauge, coasting in neutral above 45 mph actually has a higher engine load and therefore higher fuel consumption than coasting in gear (or engine braking if you prefer). Reading other posts, I understand it as your velocity being used to turn the engine so you lose speed more quickly but less fuel is required to keep the engine on.

Neutral coasts a longer distance so I think it's a wash either way for my Civic fuel economy wise. I choose to keep it in gear when I glide for the transmission's sake.

P&G beats constant 60 mph in my vehicle. But don't forget about Drive With Load. I DWL most of the time and P&G on a few rare occasions when traffic lets up.
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Old 08-22-2012, 09:47 PM   #29 (permalink)
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I used to drive a Chevy Aveo automatic trans (rated at 23 city / 31 highway) and on my 11 mile (one way) commute to school I learned that p&g was the best solution. Driving at a constant speed would get me about 29-32 mpg on any given day. Driving with load would give me 31-33 mpg, and finally, p&g would give me 35-44 mpg. I did p&g with putting my car into neutral and it didn't cause any problems, it just raised my mpg substantially. When I accelerated, I was usually able to keep the engine load around 70-80% without causing my car to downshift as long as I was maintaining the right speed. 60-45 mph was the sweet spot range for p&g in my aveo. As long as your car can smoothly shift from neutral to drive when you travel at speed, which I imagine it will, then I highly recommend doing p&g with neutral coasting (engine on, of course).
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Old 11-01-2012, 03:06 AM   #30 (permalink)
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Now this is not at all conclusive evidence, but in my auto P&G got me about 15-20 % over EPA while steady speed got me about 20-25% over. I think P&G has more potential for better fuel economy because the power is being produced more efficiently at high torque and low rpms, but it is much harder because it requires a lot of active driver participation and it's easier to brake more or go faster. But I totally agree: test it out with your own car and see what you get, but be willing to give P&G a second chance if you don't get good results the first time. It's a much harder technique to master. Flat land and long trips and traffic lend themselves more to steady speed while hilly driving and shorter trips and little traffic lend themselves more to P&G. And there's no reason why you can't stay in drive, P&G, and prevent downshifts. Just change the speeds you pulse and glide between. I personally have found that (45-50)-55 MPH P&G works best for me

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