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View Poll Results: How do you Pulse and Glide your diesel vehicle ?
Accelerate slowly, glide with the engine off. 3 5.00%
Accelerate slowly, glide with the engine on. 25 41.67%
Accelerate briskly, glide with the engine off. 4 6.67%
Accelerate briskly, glide with the engine on. 19 31.67%
I'm using another technique. 9 15.00%
Voters: 60. You may not vote on this poll

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Old 01-16-2011, 08:53 AM   #11 (permalink)
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Quote:
Originally Posted by Arragonis View Post
How do people find others reacting to P&G ?
I had one passenger assume my truck was a hybrid.
A lot of people don't notice it at all.
Or we will be several miles into a trip when they suddenly ask "what just happened?"

Other drivers don't seem to notice, but that is probably because at the high end of my pulse I am going slower than most people find acceptable, so they pass me either way.

I have had a couple instances where someone honks or flashes brights when I am in the slow lane of a 4 lane (each direction) highway and there is almost no other traffic. I really wish I could find out what is going through their minds.

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Originally Posted by Piwoslaw View Post
A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 01-16-2011, 12:55 PM   #12 (permalink)
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It may depend on the definition of P&G.

I look to maintain 1,700-1,900 rpm for all loads and roads (with a few exceptions). On this truck I think of the throttle as being useful only for changing gears, up or down. The gear selection is what counts. Other than that I drive so as to "never" have to accelerate, idle or brake. But as this truck weighs in excess of 7,400-lbs I'm quite cautious about non-limited access roadways where traffic or pedestrians could appear at any moment and default to greatest potential control of the vehicle.

I wouldn't consider actually turning off the engine while underway, and am conservative about placing it in neutral (generally gliding up to an unavoidable stop). I utilize trip planning to make the most of the truck, and have no use for trying to eke out the last few drops. (Do errands during the week and use it not at all over the weekend, for example).

Combining all trips into a long loop back to the house (city), and maximizing steady state conditions (highway), is the strategy at present.

Fuel economy is only one indicator of most work over the most miles for the lowest cost. Tire life, brake life and generally lowest-wear-per-mile count more for me as they are more informative, IMO. With a single repair at 150k and tires/brakes lasting over 120K it's so far going okay. At 170k/4k I am about halfway to the CTD MTBO in miles & engine hours (and projected 15-year lifespan).

If I drove an air-conditioned go-kart I might be more lenient about operating parameters.

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Old 01-16-2011, 06:45 PM   #13 (permalink)
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Originally Posted by Vekke View Post
scangauge works only with certain driving technigue where it is at the moment calibrated.
I see your point.

My SG has been under-estimating the average FC and has caused a bit of premature enthusiasm.
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Old 01-18-2011, 04:26 PM   #14 (permalink)
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Pulse and glide isn't very effective on a diesel if it works at all, so I don't do it. Diesels work best at constant loads near their peak torque rpm. Just get into the right gear and cruise.
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Old 01-18-2011, 04:48 PM   #15 (permalink)
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Quote:
Originally Posted by ConnClark View Post
Pulse and glide isn't very effective on a diesel if it works at all, so I don't do it. Diesels work best at constant loads near their peak torque rpm. Just get into the right gear and cruise.
For NA Diesel yes, for Turbos maybe no.
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Old 01-18-2011, 04:53 PM   #16 (permalink)
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Quote:
Originally Posted by Arragonis View Post
For NA Diesel yes, for Turbos maybe no.
Why not for turbo diesels?
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Old 01-18-2011, 06:00 PM   #17 (permalink)
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Originally Posted by mnmarcus View Post
Why not for turbo diesels?
I meant the point. I agree for NA diesels maybe P&G is not useful (albeit depending on weight vs torque) vs turbos. For TDs I think P&G has all sorts of possibilities...
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Old 01-18-2011, 06:13 PM   #18 (permalink)
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I thought that too, at first.

I posed the question here, and it was explained to me:

P&G is only partially about throttle plate efficiency.

More than that it is about using all available power (engine at full load produces more power per unit fuel than at partial load, and acceleration increases load) and minimizing internal engine friction losses (which is where the majority of the power goes in any internal combustion engine).

To put it in more practical terms: it only takes about 5 seconds for me to accelerate from 45 to 55. During that time I am getting very poor mileage (maybe 10mpg).
But it takes 15 seconds to coast back down to 45 again,during which I am getting infinity mpg (EOC). That gives me an average, over the course of those full 20 seconds of around 40mpg, which is far more than I would get at steady state (which is around 25).

The theory was confirmed when I actually started trying it, and my overall long term average increased 5mpg (from about 25 to 30)

EDIT: BTW, my truck is NA
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Quote:
Originally Posted by Piwoslaw View Post
A few months ago I returned home just as my neighbor pulled into his driveway. It was cold (around freezing) with some rain and sleet, and he yells to me: You rode your bike? In this weather?!?

So the other day we both returned home at the same time again, only now the weather is warm, sunny, with no wind. And I yell to him: You took the car? In this weather?!?
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Old 01-18-2011, 06:27 PM   #19 (permalink)
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Quote:
Originally Posted by Arragonis View Post
For NA Diesel yes, for Turbos maybe no.
I'm pretty sure it's mostly about gearing just like with any vehicle/engine. If the vehicle doesn't have gearing that puts the engine in a nice part of the BSFC map when cruising then the driver would need to P&G to see better mileage. This can happen w/ a diesel, gasser, even LPG powered vehicle. The specifics depend on the gearing versus BSFC map, but it's possible to have a TDI w/ poor gearing given the power requirements when cruising.
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Old 01-18-2011, 06:39 PM   #20 (permalink)
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P&G with diesels may have diminishing returns depending on your average speed. A constant speed will have less aerodynamic loss than a P&G with the same average speed. But again, a diesel is at it's most efficient when delivering 90% torque at it's torque peak.

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