You CAN Get Good Mileage in a Pumpe Duse

My '04 Jetta is pretty well broken in now with 50,000 miles on it. Last tank I decided to check my fuel mileage. Filed up to the brim each time (vented tank). I got 50.45 MPG! This is in mixed (about 50/50 city/highway) driving in Northern Virginia, mostly during rush hour. I did attempt to drive as economical as possible, limiting speed to about 60 and coasting in neutral when advantageous and turning off the engine at exceptionally long traffic lights.

--Nate

*steps in, looks around, whistles....

Good info!

I'd like to see what another long-term '04 PD owner, Dan- Jettafock is getting in his PD Jetta.

Dan, you around and listening?

out of curiosity...what wheel/tire combination are you running?

I have had similar results in my 05 pd wagon when taking it easy, after 40,000 miles the motor really freed up alot. I'm consistantly getting 650 or 700 mile vented tanks.

04PDWagon said:

out of curiosity...what wheel/tire combination are you running?

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The original Michelin Energy tires and alloy wheels.

--Nate

dave333 said:

Good info!

I'd like to see what another long-term '04 PD owner, Dan- Jettafock is getting in his PD Jetta.

Dan, you around and listening?

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His is a slushbox, same as mine. I got 49 mpg average for May, but I ran the 506.01 oil the entire month and the taller tires for most of the month, so take it for what you will....

Thanks, Rob. Are you really a Viking?

dave333 said:

Good info!

I'd like to see what another long-term '04 PD owner, Dan- Jettafock is getting in his PD Jetta.

Dan, you around and listening?

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Different Dan but I have a PD Jetta too. I just got 50.58 mpg on a tankful. Was about 75% highway at 70mph and 25% city. Stock everything burning D2 with the A/C on. 43K miles on the car. I coast a bit in town but never turn off the car while driving.

I have a 2004 Jetta wagon PD 5 speed that only had 22,000 miles on it when I got it used in January. I have put on roughly 2000 miles and was some what disappointed with my miles in the winter months as I was only getting around 40mgp. However I was still learning about how to drive for good mileage, foaming of diesel, and had not used any additives. Also I had snow tires on and now have falcan Ziex512 pumped up to 45PSI.
Well, I have got my first 700 miles on a tank full. I have the ventectomey and am sure it was filled to the top as I waited for all the foaming to stop and filled it to the tippy top. 49.15MPG and 75% city driving. I have really learned to watch my driving habits. I also added 8 oz of PowerService to the tank.
Next I'm going to try for the magic 50 MPG.
Jim

Nate, you are coasting in neutral!?
usually that wastes fuel unless you are doing after shutting off the engine!
leave it in the right gear when coasting and i bet you'll eke more mpg.

eli said:

Nate, you are coasting in neutral!?
usually that wastes fuel unless you are doing after shutting off the engine!
leave it in the right gear when coasting and i bet you'll eke more mpg.

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How could coasting waste fuel? If it is in gear and idling the transmission will slow the car down. I'm not following your logic.

Coasting in gear shuts the fuel off, none, zero. Not much differance but a little less then idling. Diesels do not have much of a braking effect because there is no throtle plate in the intake manifold.

If the engine is running it is using fuel. No way around that. If the engine is burning no fuel then it's RPM is either Zero or rapidly approaching it. If so and it is in gear then it will be rapidly slowing down. If you have an engine that will run without fuel I want to buy it.

Nate said he was doing 60...60 is way above the idle speed in 5th. So if he is coasting in gear he is slowing the car down.

Either we are talking about different things or you are telling me the laws of physics don't apply to your car. Hoping it is the first.

Hey thatvwguy...

I had VAG-COM hooked up to my 2004 Golf (PD) during some road tests.

When coasting downhill, in gear, the ECU reports 0 *zero* fuel consumption.

Phred said:

Hey thatvwguy...

I had VAG-COM hooked up to my 2004 Golf (PD) during some road tests.

When coasting downhill, in gear, the ECU reports 0 *zero* fuel consumption.

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Don't have a VAG-COM so I don't know how the readout looks as far as decimal places and rounding. I would suspect an indicated zero means near zero. I will stick with that theory till someone can explain to me how an engine operates without fuel.

It is the bsic principle of the internal combustion engine: Fuel - Compression - Ignition. Remove one element and it won't work.

and when the car's inertia is turning the engine over, it doesn't need to work...

thatvwguy said:

If the engine is running it is using fuel. No way around that. If the engine is burning no fuel then it's RPM is either Zero or rapidly approaching it. If so and it is in gear then it will be rapidly slowing down. If you have an engine that will run without fuel I want to buy it.
Nate said he was doing 60...60 is way above the idle speed in 5th. So if he is coasting in gear he is slowing the car down.

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Fuel injected engines cut off fuel on decel above a preset RPM. On the TDi it is around 1100 RPMs

Phred said:

Hey thatvwguy...

I had VAG-COM hooked up to my 2004 Golf (PD) during some road tests.

When coasting downhill, in gear, the ECU reports 0 *zero* fuel consumption.

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Never stops fueling while the engine is running . The Vag-Com reads "0" becasue the value is out side of the range that Vag-Com can read .

But the engine nevers stops fueling even in overrun condition . A small amount of fuel is always being pumped while the engine is running . In overrun condition the timing , the Injection Quantity & Duration are cut back to a minimum but never shut off completely .

From what I've read the PD is capable of hitting some really high mpg numbers if we can modify the ECU to force the timing to always be earlier BTDC .

From what I've read 60 mpgs coould be hit with regularity in the current TDIs in a A5 body if we can make the timing changes .

The timing changes are going to jack up the NOx , but the NOx regs are bull anyway .

DPM said:

and when the car's inertia is turning the engine over, it doesn't need to work...

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Yes, but it will be slowing the car down due to the internal friction of the engine and the resistance of the compression. That is my point - you cannot coast in gear as far/fast as you can out of gear. Anything that slows you down negatively impacts your potential mileage.

If you don't believe me find a hill in a remote area. From a dead stop with the engine not running coast down the hill in gear, make a note off where you stop then drive back up to the top and repeat with the engine off and not in gear. I will bet you a million dollars you will go further and faster not in gear.

rotarykid said:

Never stops fueling while the engine is running . The Vag-Com reads "0" becasue the value is out side of the range that Vag-Com can read .

But the engine nevers stops fueling even in overrun condition . A small amount of fuel is always being pumped while the engine is running . In overrun condition the timing , the Injection Quantity & Duration are cut back to a minimum but never shut off completely .

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This must be new science.
To prove to yourself whether or not there is fuel getting into the cylinders on decel, shut off the engine and listen/feel the difference (must be above 1100 RPMs.
No difference means no fuel was in the equation..

Alright enough with all the science mombo jumbo about thermodynamics and physics.

To get back onto the oringal topic, im getting 43-45mpg at the moment on the past few tanks (mix of 75 highway and 25 city). Changed the oil to 507 and filters as well (minus fuel, need tools for that doh!). On highway I estimated I was getting near 50 and a crusing speed of 70ish but forgot to fill up when I got into town to make sure.


I am going on a 300 mile trip next week and will test it out once more, maybe if I stay at 65mph I can get 50mpg. Just a hard time not speeding on the highway here in Texas. Texans seem not to like speeds less than 75.

eli said:

Nate, you are coasting in neutral!?
usually that wastes fuel unless you are doing after shutting off the engine!
leave it in the right gear when coasting and i bet you'll eke more mpg.

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Plus that not considered "real world" driving.

My A5 Jetta TDI is within an inch of overall length of my previous '96 B4 Passat TDI, and it is very close to the same weight, too. The A5 is P-D, the B4 obviously wasn't. Fuel consumption during normal driving is about the same. (5.2 - 5.5 L/100 km)

I can easily get better than 50 mpg if I keep the cruise on and keep it below 70 mph indicated on the highway (Interstate, little or no stopping). In town around 36 mpg normal driving.

Here is how I finally figured it:

Car in gear, moving X MPH, you need to come up with enough energy to keep the car moving at that speed, and keep the engine moving at n000 RPM.

Car coasting in neutral with engine on, moving at X MPH, you need to come up with enough energy to keep the car moving at that speed, and keep the engine idling at 800 RPM.

Since all other things are equal, more energy is used keeping the car in gear. The "savings" from stopping fuel flow to the engine while in gear is an illusion, because (as thatvwguy points out), it is stolen from somewhere else.

That having been said, coasting in neutral always makes you go faster than coasting in gear. If you got fast enough, then the dramtically increased air drag might start to count for more than the increased RPM drag.

But, to bring it back to the real world. Since I have started doing all my coasting in neutral, I have gained 5 to 10 MPG.

thatvwguy said:

Yes, but it will be slowing the car down due to the internal friction of the engine and the resistance of the compression. That is my point - you cannot coast in gear as far/fast as you can out of gear. Anything that slows you down negatively impacts your potential mileage.

If you don't believe me find a hill in a remote area. From a dead stop with the engine not running coast down the hill in gear, make a note off where you stop then drive back up to the top and repeat with the engine off and not in gear. I will bet you a million dollars you will go further and faster not in gear.

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I have gotten as low as 41 and as high as 53 with my 04. I found out I get the best mpg if I set the cruise at 70 mph, have the tires at 40 psi. If I cruise at 75-80 mph, I get 47 mpg.

What was your speed for the 53 MPG? My best last night, and it took discipline, was 56.7 driving 55 on a 140 mile highway cruise. Crank up the Phatbox, lean the seat back, and watch numbers I never thought I'd see on the SG.