What is venting and why does my car not get the mileage i see others achieving?

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Highway slow speed is nothing compared to the savings in mpg if you drive like there is a raw egg under your shoe on the pedal on in town and stop and go. Not letting it idle lower as you let out the clutch. 90% of all your gains are in city driving. It's easy to get 50mpg on the highway. If you go long enough to make it count, tape up all the seams on the body and draft behind a semi doing the speed limit or more.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
I got my best mileage (52) on a trip thru the Applacians, 70+ the whole way. I believe the VE is very efficient at high RPMs.
 

jayb79

Top Post Dawg
Joined
May 20, 2000
Location
Exeter,NH
I did a hypermiling experiment a few years ago in my golf and was able to get almost 90 mpg in town driving, rarely touching the go pedal. Was probably the longest 100 mile driving experience of my life couldn't do it again but it's doable and not good for anything or anyone (especially the poor people behind me).
 

Lightflyer1

Top Post Dawg
Joined
Sep 13, 2005
Location
Round Rock, Texas
TDI
2015 Beetle tdi dsg
To the OP. You are actually in the mid or better part of the bell curve, so not so measly. Sometimes we read here the exploits of a few and think that is the way it is for everyone, it isn't by far, as you can now see.
 

IndigoBlueWagon

TDIClub Enthusiast, Principal IDParts, Vendor , w/
Joined
Aug 16, 2004
Location
South of Boston
TDI
'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW


Just filled my Wagon this morning: 803 miles, 15.8 gallons = 50.8 MPG. This tank was some commuting (30 miles round trip, 80% highway, some traffic, usually at 80 MPH otherwise); and a round trip to NYC. NYC trip is about 475 miles, some traffic, 75-80 MPH most of the time, but this trip I had an extended run at 90+ MPH because that's how fast the traffic was moving. I expected to take an FE hit because of that, but not so. A/C on for most of the tank: It's been hot and humid here.

I'm sharing this because a properly set up TDI can deliver really good FE without any special driving techniques. I use the cruise and A/C when I want, accelerate hard occasionally, don't hesitate to rev the engine to 3500-4000 RPM occasionally. I do have 15" wheels with stock tires, and a .700 5th gear which drops highway RPMs by 150-200, depending on speed. 75 MPH is 2400 RPM, for example. I think this helps quite a bit. I also have some PD150 breathing mods and a downpipe without a CAT which might help, although my Golf with a stock exhaust delivers similar FE.

Make sure your car is in top condition (injector condition, correctly set mechanical timing, clean intake, vacuum system working properly, turbo boosting correctly, and so on. And keep in mind that it appears that some cars simply deliver better FE than others. Not sure why, but I've experienced this with the TDIs I've owned over the years.
 

Curious Chris

Top Post Dawg
Joined
Jun 11, 2001
Location
Pineview GA
TDI
Jetta Wagon 2003 RIP Rockford IL
Yes I think the rule is the diesel is happiest at 80% of torque curve. Which on an ALH the torque is constant to 4200 rpm then drops. So 3200 rpm would be pretty fast so maybe just 3000 which is 80mph in a ALH with manual transmission.
 

Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
"it appears that some cars simply deliver better FE than others."

It is commonly accepted that your feet on the pedals is the single biggest factor for FE. I suggest that tires are likely the 2nd biggest part of the equation. My oversize sticky tires are NOT conducive to mileage, and I'm certainly not shy about using the mods on my ride. But what hasn't been mentioned is the odometer itself. I know that when I went oversize
I noticed a change in the speedo by approximately 3 mph referenced with GPS. Back of the envelope calculations bear
out a change in the odometer by a couple of %. I'm not fussed by the fact that it now reads a bit less than miles actually
covered, but is undoubtedly a factor in calculating my mpg.

I've been told by tuners that the ECUs often have different software iterations. Overall they may be very similar, but differ in detail. Without rigorous carefully measured consumption rates per mile per individual vehicle, it's a bit hard
to tell exactly what "I get X miles a tank" translates to precisely. Clearly speedos, and I'd suggest odometers as well, can be different. Bragging rights I believe tend to skew the #s as well.

I for one am not fussed about squeezing a couple extra miles per gallon. I'm happy that I'm getting great bang for the buck out of my car. And I'm with IBW on the rev range, my butt dyno tells me the engine is happy, and economical,
circa 2400rpm.

My wooden $ .05
 

jettawreck

Top Post Dawg
Joined
Aug 2, 2004
Location
Northern Minnesota-55744
TDI
2001 Jetta and 2003 Jetta
It has little to do with engine rpm. Mostly air/moving resistance. You can't cheat physics and once you start to exceede 60 mph the wind resistance becomes the biggest factor to overcome. You can minimize air resistance "drafting" in traffic (you don't really have to be NASCAR close to the lead vehicle, even several car lengths make a big difference) but you won't find me doing it for two reasons-safety (obviously) and I don't have traffic to deal with/drive in. Very rural environment here.
Tires are probably often overlooked. I run a bit oversized 205/65-15 which brings the speedo close to actual but cause the odometer to under report by 2.5%. Drive 40 miles and I record 39. 40psi gives a decent compromise in lower rolling resistance, ride quality and tire wear.
Never have messed with IQ settings. Old Bosio Sprint 520 nozzles with injection timing advanced static and in adaptation.
Yesterday the 2003 filled up at 900.1 indicated miles (had to drive around the block to break 900, which is actually about 922 miles) and filled to the rim at 16.22 gallons. 55.28 mpg for the tank (56.6 mpg if using the corrected miles calculation). Seldom over 65 mph as most of the rural two landers are 55 mph limits anyways. Almost all that tank was driving back and forth to a work project of 80 miles each way. Mileage will start to drop off as colder freezing weather is the morning normal recently.
The 2003 car has always done a bit better than the 2001 regardless of where I've set timing, etc.
 
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