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Old 04-16-2020, 04:42 PM   #3 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
Posts: 718

TDi - '04 VW Golf
90 day: 50.21 mpg (US)
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Pulse and Glide. As I stated in post #2 above- Coast when it is practical. If you are new to Ecomodder you may be amazed by the mpg numbers posted by some members on this site. Often the highest mileage is obtained by using Pulse and Glide. (Also know as EOC which stands for Engine-Off-Coasting.) Using this technique drivers accelerate to a target speed, say 60mph, and place the shifter in neutral and kill the engine. They coast or glide with the engine off to, say 50mph, and bump start the engine by putting it back in gear and letting out the clutch. This can be a way to get great numbers with a gasoline engine. DON'T DO THIS IN YOUR TDI! Ignore this at your own peril.

Here's why. #1- Diesel engines are very different from older gas/petrol engines. Gasoline engines have a throttle plate which does just what it sounds like it does. At part throttle it chokes off the intake air to maintain stochiometric ratio. This is good for combustion of gasoline but bad for low demand or idle fuel efficiency. In EOC Ecomodders install a kill switch near the shift lever to ground out the spark till the engine dies. They can glide with the engine off without turning the key. This avoids low load inefficiency and allows for glides using no fuel whatsoever. A diesel can burn at variable air/fuel ratios and are very efficient at idle. This means that there are much lower pumping losses at idle because there is no throttle plate and no vaccuum created and hardly any fuel is being injected. On my TDI I can coast (or glide) at 400mpg with the engine idling. There is no need to kill the engine to get good mpg numbers.

#2- Because the TDI shuts off the engine by not injecting fuel, it is much more complicated to kill the engine. I do not recommend using the key to do this. It not only shuts off the engine, it disables the airbags, vaccuum for power brakes goes down (the running engine turns a vacuum pump), no more power assist steering and it stops oil flow to the turbo. If your turbo has been running hard this is very bad! Don't do it.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.

Last edited by COcyclist; 07-15-2021 at 04:48 PM..
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