Working on my 2005 TDI Diesel to get better MPG

Very good point about lifting off the gas sooner than later. Also, get a run going down hill and let the inertia get you over the top by lifting slightly before you reach the top. I think most people in the U.S.A. try to maintain speed too much. (cruise control is , in the long run a waste of gas if not used properly) . If they would "drive right", like Europeans, it would save an enormous amount of fuel AND allow drivers to calm down a little bit. "DRIVE RIGHT" as you know, means lots of things, including all trucks convoy in the right lane and never change lanes except to get off, all drivers choose a lane to be in and stay there, ABSOLUTLY NO TAILGATING ALLOWED, (cuts down on road rage) This obsession we seem to have with changing lanes just to fill in the gaps is absurd. Road rage and lack of patients is the biggest waste of fuel by far. V W has always had a handle on fuel economy.

I used to play a game in rush hour traffic (which lasts all day now), where I tried not to use my breaks much, and I didn't speed up too much. By leaving a good gap in front of me allowed me time to "coast" , and when the car in front of me slowed to a stop, I usually did not have to break before they sped up again. "eggs on top" is a great way to look at it. This system works well except for one thing, no one will let "gaps" exist, and the drivers (including trucks) are constantly changing lanes. All a part of road rage in congested traffic.

If you think of what happens to an engine when your starting in cold temps, you then can understand that this is a condition by which you would not want to operate under. As the engine tries to fire when it is cold, more fuel is placed into the system; ie, cylinders. Having this condition on all of the time (if this is what your friend is stating) is not good. I would suggest as others might state. Keep your foot out of it.

Just think why would manufacturer had not chosen to do so? there must be some trade off.

Leave tinkering with factory settings alone. But diesels have their efficiency sweet spot at 1600-1800 rpm, and wide open throttle around 80% of the max. power output. There the VW motor alone runs around 34% efficiency, which is darn good.

There are safer ways to pick up mileage than that resister.

Remove your windshield wipers when it is not raining. Have a very low restriction exhaust system fabricated.

Remove any exterior emblems that are in the air flow.

Keep your tires at the maximum safe pressure. When replacing tires, shop for high mileage variations.

Make sure there is as little tow in as allowable.

Dump the weight out of the car.

Look at the aero tricks done on some of the racing circuits, and copy them.

I had an older Ford 6.9 diesel that I desperately needed to get better acceleration out of. I also advanced the timing. I paid for this with early burn outs of the glow plugs. I was willing to live with this. Do you?

I've have made several inexpensive modifications 2000 TDI Jetta with the goal of improving miles per dollar.

Here are some successes that I can recommend:

1. FUEL :

Use a quality fuel with a cetane rating of at least 40.

I am in Florida most of the time, so i amup at Chevron or Shell or Exxon to get cetane of 40+... Fuel from the same company but sold in different states can have different cetane rating, so check locally. The fuel is more expensive, but additional cost is more than offset by the increase in MPG.

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2. TIRE PRESSURE:

Maintain a high safe tire pressure... monitor and correct regularly, e.g. at every fuel refil . 90% of max side wall pressure is what i maintain.

l 3. Reduce loads on the engine...

...use the lowest viscosity recommended motor allowed for your climate.

Keep brake pads from dragging on rotors when not breaking.

.. 4. Add battery capacity, and recharge with good charger from residendial electricity daily. Wall power here costs me a little under 11¢ per KWH, which is easily 5 times less expensive that the cost of generating AC via alternator. t

As much as 20% of fuel consumtion goes to turn the alternator, so there are huge rewards to be had.

In actual mixed city frmpgeeway driving my TDi multitank average is just under 53 mpg.

....speaking to the OP's actual question, I believe the idea of having the fuel temp accounted for as colder than actual, is that the calculation assumes a higher fuel density at colder temperatures, so less volume is pumped.

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The same effect can probably be produced by moving the driver's seat back or placing progressively more still springs under the accelorator...... until it is difficult to push the accelerator down fully/ or as far as usual.

....A decrease in fuel consumption and rate of travel are probable..

I believe that colder readings would result in richer settings from the ECM.