What I have learned about PD TDI FE

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
This is my first post under this account. I had a past account, but never really posted and lost the information. I have mainly lurked for many years. With that said...

I have a daily commute of about 84 miles round trip. My FE seemed to hit the wall around the 47 to 48 MPG mark in warm weather, and 45 to 46 MPG in cold weather. A few months back I decided to try something new. About 20 miles of my commute is getting to highways (round trip). I wouldn't call it hypermiling, but I stay in neutral as much as I can getting to the highway. I do not do this on the highway. Since doing this, my MPG have been over 50 for the last two tanks. My Scangauge II is reading over 50 right now, and is for the most part close. I also do not turn off the engine at traffic lights.

This is my hypothesis: I use Shell Rotella T6 5W-40. When the temps are below 60 degrees the oil is thick (I am sure most oils are). Free wheeling in neutral allows for the oil to warm up and does not cause drag. While idling doesn't warm up the engine much, by the time I am on the highway I am at operating temps. On cold days I would see my MPG average drop by 1 to 2 MPG getting to the highway. On warm days 1 MPG wasn't out of the norm.

Also, on the highway going 70 MPH (SG II reading) temps under 60 dergees my MPG would be lower on average than days over 60 degress. I am thinking about a grille block for the top half. The area around the VW logo. I think the grille block will serve as a benefit for aerodynamics and warmer operating temps. I think much of this might be how the PD is programmed, and/or how much fuel is used for keeping speed and going up hills.

Let me know what you think. This is my second TDI. My first was a 2003 Jetta wagon. My best tank with that car was 55 MPG in 810 miles. That was a road trip from NJ going to SC.

Thanks, and any advice for better FE is welcome.
 

psd1

Veteran Member
Joined
Aug 4, 2011
Location
OR
TDI
2006 Jetta 2013 Passat SE 6Man
I think you are spot on with you ideas, and you MPG's are great. I only commute 20 miles one way so if its real cold when I start out my temps don't get up to a good temp until 7-8 miles in. I try to coast as much as possible as well. It looks like you have about a perfect commute to get great mileage.

I was looking at your fully acct and it is very similar to mine. I have been testing for GDE and attribute my numbers to their tune(s). I am very anxious to see what I can do with straight D2.
 

tditom

Top Post Dawg
Joined
Sep 5, 2001
Location
Jackson, MI
TDI
formerly: 2001 Golf GL, '97 Passat (RIP) '98 NB, '05 B5 sedan
rolling in neutral=engine consuming diesel to keep working

rolling in gear=no fuel used
The other part of this equation is how far do you roll in neutral compared to when you are rolling in gear?

Both methods have their time and place.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
Both methods have their time and place.
This is the most important thing that folks seem to forget. Imagine a long hill. I like to keep it in gear and let the engine keep the speed in check with just small applications of brake. Then when I get near the bottom, take it out of gear and speed up just a bit and coast farther before having to apply fuel again.
 

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
I think you are spot on with you ideas, and you MPG's are great. I only commute 20 miles one way so if its real cold when I start out my temps don't get up to a good temp until 7-8 miles in. I try to coast as much as possible as well. It looks like you have about a perfect commute to get great mileage.

I was looking at your fully acct and it is very similar to mine. I have been testing for GDE and attribute my numbers to their tune(s). I am very anxious to see what I can do with straight D2.
My overall average would be higher on Fuelly if it wasn't for last summer. I am a science teacher, and last summer there was no extended school year or summer camp programs. So I found a summer job that was close to were I live. With AC on all the time and a round trip of about 10 miles my MPG took a hit. I was around the 38-39 MPG mark. I know if I was coasting more I could have been around 44 MPG.

I have been thinking hard about the grille block. I know many aero modders use coroplast; however, I can only get the larger size panels online. I have been trying to think of another material I could use that is easier to buy. I am also curious about how the summer heat and the grille block will affect my FE in the summer. The Eccomodder forum points to higher intake temps for better FE (summer and winter). Once I thought about why, it did make sense. I will keep my findings posted here. I plan to block the upper grille and the fog light areas.

Thanks!
 

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
rolling in neutral=engine consuming diesel to keep working

rolling in gear=no fuel used
Any type of braking, engine or stopping, is wasted energy and a loss of momentum. Before I changed my driving style I was engine braking or staying in gear during down hills. Being in neutral during a down hill can have a few affects. You can allow gravity to keep your speed or gain some. However, it also changes how you enter and finish these situations. Such as, if you are on a down hill you can be in neutral to engage the up hill that is coming up.

All of this is depends on the situation. In the 10 miles it takes me to get to the highway, I am in neutral for most of it. I could not do that rolling in gear unless I constantly accelerate after losing speed. It actually amazed me how long I could be in neutral and still be going near the speed limit.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
Hans, you should try a 6% grade for three miles. You will find that having it in gear helps.
 

psd1

Veteran Member
Joined
Aug 4, 2011
Location
OR
TDI
2006 Jetta 2013 Passat SE 6Man
Hans, you should try a 6% grade for three miles. You will find that having it in gear helps.
I have three 6% that are 2 miles and I generally coast out of gear until near the end of the last one. I'm still not sure if I would get better economy in gear because I couldn't get as far up the next one without the momentum.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
On 6% grades in gear I need to tap the brakes a bit to keep from exceeding the speed limit by too much. If I let it freewheel, sure I could go farther on the bottom, but as Hans mentioned, for me the biggest factor is safety.
 

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
There are many variables such as curves, traffic, traffic flow, and weather. All of those situations change how we drive. While neutral rolling works very well for my commute, it may not for others. Most of the highway speeds I travel on are 65 MPH. At that speed I would get pushed off the road. At 70 MPH I am not the slowest, nor am I even close to the fastest. At 70 MPH I do not have to brake for slower traffic, and do not get in the way of faster traffic. My commute has rolling hills; I have been using cruise control to baseline my commute getting to the highways. Seems the third tank will be over 50 MPG also. So neutral coasting works for me.

Once I get around to the grille block I will still use cruise control and out of gear rolling. That baseline will tell me if the grille block works. I was close to 53 MPG (SG II reading) until I hit stop and go traffic twice on the highway due to accidents. However, having a few traffic jams is real world data. I am fairly certain that with the grille block, neutral coasting, and no cruise control 55 MPG is attainable. Once I three tank average that, I will test some air damns before the front and rear tires.

My goal is to consistently average over 50 MPG while driving normally in terms of speed and ease of use. I want real world numbers, not driving slow creating havoc. I am also certain people do not even know I am coasting when they are behind me. I think it is a misconception that slow speeds are needed to get high rates of MPG. Foresight might be the biggest factor along with environmental conditions. Anticipating highway exits, traffic lights, and other “events” can improve FE in a commute. Driving at a slow speed lessens the effect of needing to lose momentum. However, high speeds create another issue, aerodynamic drag. While the A5 Jetta is clean, there is much room for improvement. Most of this improvement can be achieved without changing how the car looks.
 

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
Just an FYI:

With the increase in temps outside I just got 51.5 MPG. My three tank average is 50.8 MPG. Now I need to find a good material for a grille block.

Somethings tells me I am getting better MPG around town than on the highway.

Anyone have an idea about what I can use to block the grille?

Thanks!
 

psd1

Veteran Member
Joined
Aug 4, 2011
Location
OR
TDI
2006 Jetta 2013 Passat SE 6Man
Just an FYI:

With the increase in temps outside I just got 51.5 MPG. My three tank average is 50.8 MPG. Now I need to find a good material for a grille block.

Somethings tells me I am getting better MPG around town than on the highway.

Anyone have an idea about what I can use to block the grille?

Thanks!
Thats good mileage, I had a 50.5 MPG avg over 3 tanks a while back, it's now 48.5. What makes you think your city is better than your highway mileage?
 

MikeMars

Veteran Member
Joined
Mar 6, 2008
Location
UK
TDI
Vento 1.9 TDi (retired), A4 1.9 TDi (rear end collision), VW Passat 1.9 TDi (retired), Audi A2 1.4 TDi
...
Somethings tells me I am getting better MPG around town than on the highway.
...
Highway MPG is mostly determined by aerodynamics. So if you are getting particularly bad mpg from highway driving, there are two things to look at:
* Aerodynamics (roofrack, towing, etc).
* Speed (aero drag is proportional to the speed squared).
 
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Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
Thats good mileage, I had a 50.5 MPG avg over 3 tanks a while back, it's now 48.5. What makes you think your city is better than your highway mileage?
There are a few reasons why I think I am getting better MPG around town:

1- Less fuel use all around. I am idling for most of the around town driving. SC II is always showing 120 to 300 MPG.

2- Most of my speeds getting to the highway are under 45 MPH. I am not fighting drag or keeping a constant speed like that of the highway.

3- With cruise control on, SC II reports about 55 to 62 MPG depending on conditions on level ground going 70 MPH. Much of my highway travel is hilly.

The one area where I can control frictional forces and FE is around town. So I think I am getting better MPG around town. Now I just need to find some coroplast or ABS plastic to block the grille, It is harder to find than I thought.
 

Hansgruber

Well-known member
Joined
Mar 23, 2012
Location
New Jersey, US
TDI
2006 TDI
Highway MPG is mostly determined by aerodynamics. So if you are getting particularly bad mpg from highway driving, there are two things to look at:
* Aerodynamics (roofrack, towing, etc).
* Speed (aero drag is proportional to the speed squared).

I am well aware of this. I really can't go slower than 70MPH for FE reasons and safety. If I go faster I will have to slow down for slower traffic, less FE all around.
 
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