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BleachedBora January 11th, 2008 16:42

Newbies and Vets: Tips for better fuel economy!
I've thought about doing a list like this for a long time. I remember when I first started driving my 1997 Jetta TDI I saw people claiming 50+ MPG. I figured they were off their rocker because I was only getting 36 if I was lucky. I fueled at Flying J (Now Loves) in Troutdale, Oregon, ran my tire pressure at 32, and drove like I stole the thing. Over the course of over 11 years and 500,000 miles of driving TDIs later I consider myself by no means an expert, but I'd like to consider myself a very well informed driver. The following is a list that people are welcome to add to. Rules and my top 10 list might be added to and changed as well as time goes on. The point is to get a discussion going so that those that are new to our community aren't intimidated with the fuel economy numbers they are getting, as well as meaningful ways on how to get better economy.

Some rules of thumb:

Rule #1: Never trust the computer--not even a $80,000+ avionics package in an aircraft is 100% accurate with regards to the computer. (For what it's worth, general aviation fuel gauges are required by law to be accurate at only one time--empty).
Rule #2: If you want to know your mileage, fill up completely to the top every time, this is after letting all the foam settle. Take miles driven and divide by gallons (in the US) to get MPG. If you want to be very anal you must realize that if your wheels/tires are different than stock then your calculation can be off by 1-8%+. From the factory your speedo is off by ~3 MPH but your odometer is spot on. Remember that when putting on new tires, oversize tires will make your speedo more accurate, but your odometer will start to under report. My MK3 Jetta with 195/65/15 tires was perfect on the speedo, but the odometer was low by 6%.

I've been married since 29 Sept 2007. When I first met my wife she stated that her previous car got "X" MPG, which she always got off the computer display. She had a car without a computer and I had to teach her how to do MPG. She kept resetting the trip odometer when she went places to "see how far she goes." Point is that with her car which was supposed to get 28 MPG, she's had some tanks as low as 19.6 MPG. Since I first wrote this thread 6-years ago (update Oct 2014) she's had a Jetta Wagon and a Passat Wagon, she has become quite adept at calculating mileage too :).

This all brings us to:
BB's tips for higher mileage*, more or less in my order of easiness and cost effectiveness, and according to my own experience--I have multiple tanks in a row with over 60 MPG. I'm also one of the very few members to get over 900 miles in a tank WITH A MK3 (15 gallon tank when dry). Driving for mileage is hard to do unless you know what to do--again YMMV:
1) Run tire pressure at 90% of recommended max pressure as stated on side of tire. (Free)
2) Run a good quality fresh fuel with a high cetane number (see bottom of post for some stations cetane numbers). In the west Chevron seems to by far bring the best numbers. A poor quality fuel with low cetane will lower MPG by up to 5. Just because it's a truck stop it usually means you are putting crap in your tank (especially Flying J). In the Midwest BP/Amoco are great--both BP and Chevron have stated that they won't have Cetane under 49, which is what our cars need. If you're filling with crappy fuel run an additive. I personally like Lubromoly Super Diesel Additive. There are lots of writeups online of differing qualities of additives. Biodiesel up to B20 won't really have an effect on your mileage. B100 will lower it by ~5 MPG. Note that these numbers are taken with over 750,000 miles of careful calculations over the course of many years, different cars, and different seasons.
Example: If you get 40 MPG from Flying J at $4.25/gallon, and 45 MPG from Chevron/BP at $4.49/gallon, you are paying $.10625/mile with the J, and $.09978/mile with the higher quality fuel. (And if you find a quality station next to a truck stop often the difference in price is less than $.05/gallon!) You actually save $64 just in fuel over the course of 10,000 miles by buying the more expensive fuel. This says nothing for what you might save in maintenance (injection pump and the rest of the fuel system) over the course of time. Just because it's expensive doesn't mean it's good. I've called lots of corporate offices and have numbers on the following cetane levels*** (See end of post)

Most truck stops are going to be low numbers because most semi's run the same regardless of cetane number.
3) Have a good working Mass Air Flow sensor and clean filters/snow screen & non-restrictive intake. (Air filter ~$14-20 for cold region filter--run it regardless of location. $20-30 for a good fuel filter. A poorly working MAF will give you 5+ less MPG. If you are in doubt to if yours is working, unplug it and see if you have more power. If you do, your MAF is bad. If you are running a cone filter (like K&N) you don't even have to check it, it's probably bad already. A stock air filter flows better than a K&N and it won't kill your sensor. A new Bosch revision "C" MAF will run about $100 for a 1999-2003 car, and about $160 for a 2004+ car.
4) Go easy on the accelerator. Drive like you have an egg under your foot. Bear in mind that when you are coasting in gear you use no fuel until you decelerate to ~1200 RPM. You burn ~.5 quarts per HOUR with a warm engine at idle, turning your car off at lights to save fuel is generally ineffective. *I rented a BMW 520D in Germany in September of 2014. It had auto stop/start. My feelings are that when the computer controls the stop start it's going to be more effective in fuel savings then you will be doing it manually. ;) Be gentle on acceleration--if you have a boost gauge limit your boost to 5 lbs. while speeding up. There is a lot of talk about city vs highway driving. A lot of people seem to confuse city driving with slow driving - what they fail to realize is the effects on your MPG are totally different between the two. The reason city MPG is low is because you have lots of stop and go; when you are accelerating you are using a lot of fuel. A cold engine also is less efficient than a warm engine. Furthermore every time you hit the brakes you waste precious kinetic energy (speed) which cost you fuel to build up...unless you are an expert at timing lights. This cycle continues to repeat itself from stopping point to stopping point. Because of this you see low MPG. Slow (constant/rural road) driving is optimal, since you can cruise for a long time in a high gear (low RPM) without much throttle at all due to the lower amount of wind resistance (aerodynamic drag) from trying to slice through the air at a lower speed. The result is excellent MPG. Highway driving is the median MPG; you can cruise at a constant speed in the highest gear, but you are traveling faster so there is more aerodynamic drag, reducing your fuel mileage. (Free)
4a) Those in REALLY cold places (Canada and parts of US where sub-freezing temps are common) often get a bra/cover to limit air intake and/or get a Frostheater. These will help the car warm up faster and therefore be more efficient. That said, don't start the car and let it idle to warm up--it won't warm much without load on the engine and you blow any mileage improvement from a warmer engine by the fuel lost idling (and it's bad for the environment).
5) Don't go oversize on tires or wheels. If you do get larger wheels make sure they weigh the same or less than stock. I run the ENKEI RPF1 wheels which weigh 13.5 lbs (16"). The cost isn't worth it for fuel savings, but I like how they look! 18" R32 wheels are around 27 lbs and will kill your economy.
6) Get a performance chip--Malone tunes as well as TDTuning & Rocketchip are all great choices. They will give you performance when you want it, and fuel economy when you drive nicely. My experience was that Malone gave me a bit more economy over RC. You'll be happy with any that's for sure! (~$300-550 depending on car)
7) Nozzles! ('96-03) Bosch nozzles (the genuine VW T4's are excellent, not to be confused with "DLC 1019's" which are not Bosch) ~($300)
8) Downpipe --- Breathes better, gave me ~2 MPG, but it helped. (~$250-400 again depending on model). On the common rail 2009+ cars, as long as you are an off roader only (or decide to run for testing purposes) you'll find a DPF delete (roughly $550) and stage 2 tune will average a 5-8 MPG improvement.
9) Larger turbo--again better breathing leads to better economy. Hybrid turbos appear to do the best for economy. ($850-3,000+)
10) Have fun, you can be frugal and finesse the car without being a worry wart. It's great to get your first 50 MPG tank, and amazing to get your first 60 MPG tank. Be honest with yourself and others, and realistic as well. When a member goes from a 38 MPG average and then reports a 72 MPG tank no one will believe them. My gains were from 38-42, 42-48, 48-54, a ton of tanks in the 53-58 range, and then a few breaking 60. My personal record is 62.48 MPG. Not bad, especially in an MK3. Probably won't happen in an MK5 or MK6 though!

*Following this guide won't guarantee the same results, but it will guarantee better results than what you have now. I reserve the right to change this guide at any time :).
Cheers, and happy TDI'ing!

***Cetane levels by fuel company. To ensure accuracy if you have a level to add to the list please forward an email from a corporate office to me, and I will add it to the list. Please bear in mind that the current federal minimum from refiners in the USA is 40. Depending on the quality of the oil used as well as refining processes you'll find 40-42 from refiners in the US and Canada. Anything above that has to do with specific companies additive packages. When companies give a minimum value then it will be listed as a single number. When a company gives a range of numbers bear in mind that more often than not you'll probably find the lower number rather than the higher number. If 40 is listed then it generally means that fuel is bought as is from the refiner--if someone messes up and doesn't put in enough additive at the refinery then that can cause major problems for your fuel system. It's recommended therefore that if you get the inexpensive fuel with low cetane you use a cetane booster (PowerService, Lubromoly Cetane booster or Stanadyne are all great choices), or run a little biodiesel in the tank. If something higher than 42 is listed then the retailer adds their own additive package in addition to the standard refinery additive package. Generally speaking as long as 49 or higher is listed you do not need to worry about adding any additives yourself.

Worldwide published study on cetane levels.

All California Diesel: Minimum 53 Cetane (No wonder it's so expensive down there!)

Propel HPR, 75
Syndiesel, 60
BP (Amoco branded), 51;
Countrymark fuels Diesel-R, 50
Chevron, 49; or 51 with Techron D labels in select markets
ConocoPhillips through the 76 stations (California) 53
PetroCanada, 47-51
BP (Powerblend 47, Otherwise 40-42)
Shell, 46;
Sinclair, 46;
Sunoco Gold, 45 (often +1-5) Sunoco regular is usually 40.
Exxon/Mobile, 43-46
Holiday Stations, 40-43
HESS, 40-42, can be up to 45.
Husky, 40 + diesel Max additives raise another 1-3 from there (41-45 max)

Federal minimum of 40 (as per ASTM D975) - Alphabetical:
CITGO, Flying J/Loves, Pilot, Sheetz, Valero, Walmart, Wawa

rotarykid January 11th, 2008 17:39

The 1Z engine in a A3 or B4 is more than capable of hitting mid 50s tank after tank with a little effort . I've hit just over 64 mpg US twice in my 97 Passat TDI with high 50s tank after tank in city driving . I always get higher in city loops as compared to higher speed highway only loops . I always have .

Over size tires do help lower fuel consumption if you don't over accelerate . Over acceleration with taller gearing from over sized tires will use more fuel .

Only use the gears that are needed for a given acceleration . Like 1st 3rd 5th most of the time is more than adequate .

Speed shift whenever possible as this will save rpms between shifts in city driving improving fuel economy . Get into high gear and stay there as much as conditions will allow this will also save fuel .

Coasting in "N" while at lower speeds in city driving will allow you to go farther without throttle input saving fuel . Also killing the engine when coasting while the engine is still cold can save fuel using your momentum to restart the engine when acceleration is required . Killing the engine should be avoided once the engine is warmed up due to the extra heat in the turbo .

Always look far ahead in traffic to try to avoid ever coming to a complete stop . Avoid using the brakes as much as possible as every time you use the brakes you are wasting fuel .

If possible park on a hill to use gravity to start the engine the first start of the day as this will save energy lost with the first crank of the day . These engines use the most fuel while they are cold so anything you can do to reduce strain while cold will save fuel .

I have close to 8 years of records from my Passat the prove that if care is taken in city loops 52-55 mpg US is quite obtainable . And with a little effort 60 + mpg US is doable in a 1Z equipped A3 & B4 . The best I ever do on the highway is around 50 mpg US @ 65-85 mph .

Bob_Fout January 11th, 2008 18:21

Coasting out of gear or in-gear depends entirely on the situation.

Umm..NEVER turn the engine off while driving, that's crazy.

Gravity starting a TDI....

zaeli January 11th, 2008 19:13

How did you learn your wife how to figure fuel economy?
I think that's why my ex and I broke up...Good artical!
Btw she got the 04 and I bought myself and 99.5.

sadi gaddi January 11th, 2008 19:18

With due respect, I thank all of you for your tips. Its always a good learning process. Never forget - its a hobby.
Secondly, a simple question. Having less weight helps increase average. Would it be advisable to fill up only up to half tank and drive....rather than full tank. Condisering 7-8 gallons weight up to 60+ pounds.
thanks. Appreciate advise/constructive criticism.

scooperhsd January 11th, 2008 20:22

Then how are you going to know how much you used ? How full is the tank ?

I'll stick to full tanks, thank you very much...

whitedog January 11th, 2008 20:42


Originally Posted by scooperhsd
Then how are you going to know how much you used ? How full is the tank ?

I'll stick to full tanks, thank you very much...

Talking about this:


Would it be advisable to fill up only up to half tank and drive....rather than full tank. Condisering 7-8 gallons weight up to 60+ pounds.
It wouldn't matter. The mileage would be better, but it would impossible to get accurate fuel mileage readings unless the tank was filled every 2000 miles or so.

Is it advisable to run with a partial tank all the time? No because that just leaves more air in there to condensate water intot he fuel.

Bob_Fout January 12th, 2008 08:11

Doesn't matter if you fill at half a tank or 1/4 tank, the accuracy is the same if you vent.

whitedog January 12th, 2008 08:35


Originally Posted by Bob_Fout
Doesn't matter if you fill at half a tank or 1/4 tank, the accuracy is the same if you vent.


fill up only up to half tank
Two massive, yet tiny words.:D

Bob_Fout January 12th, 2008 08:40

Ooooh. I just woke up dog :D

roadhard1960 January 12th, 2008 08:46

Bob, are you saying you have a Magnaflow catalytic converter? If so you wiped out a cat in less than 80,000 miles or you just wanted bigger from the turbo back?

Bob_Fout January 12th, 2008 08:51


Originally Posted by roadhard1960
Bob, are you saying you have a Magnaflow catalytic converter? If so you wiped out a cat in less than 80,000 miles or you just wanted bigger from the turbo back?

Yup, I wanted a higher-flow cat to go along with the other exhaust mod goodies in my sig. Bigger downpipe, high-flow cat, 2.5" straight pipe, no muffler, one resonator.

roadhard1960 January 12th, 2008 11:43

What did all the exhaust net you? Better mileage, more noise, more power? Did you attach everything at the same time? Gator before all of the exhaust work? Gator before the fancy nozzles? New Gator tune after the more free flowing exhaust?

Bob_Fout January 12th, 2008 17:05


Originally Posted by roadhard1960
What did all the exhaust net you? Better mileage, more noise, more power? Did you attach everything at the same time? Gator before all of the exhaust work? Gator before the fancy nozzles? New Gator tune after the more free flowing exhaust?

Better sound, more power in that the power band is wider (turbo spools MUCH quicker), and most important, lower EGTs. I don't know if my MPG got any better, but I did average 52 MPG driving to and from Florida driving 65 to 75 MPH immediatly after the exhaust work done. I still just had nozzles then.

I did the nozzles last April, did the exhaust all at the same time about 3 months ago, loaded my Gator tune about 2 weeks ago.

DFWDieselJet January 12th, 2008 17:27


Originally Posted by BleachedBora
You burn ~.5 quarts per HOUR with a warm engine at idle, turning your car off at lights to save fuel is dumb and ineffective.

PD engines burn around .3 GALLONS per hour at idle once warmed up (a little less - yes LESS - until they are warmed up), so turning off the engine is (arguably) more beneficial than with a non-PD engine. Verified on an '04 Jetta, both with ScanGauge and VAG-COM.

I and others have seen a 5% increase in fuel economy by turning off the engine while driving or at long lights, so it can be effective. Whether it's dumb is debateable. (But not here please, this is a great thread!)

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