Newbies and Vets: Tips for better fuel economy!

I originally wrote this for TDIclub back in 2008. Posted with some revisions.

20 years ago 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 a decade and 500,000 miles of driving TDIs I considered myself a very well informed driver. The following is a list of tips and tricks for those that may not be getting the fuel economy they thought they should be getting. This is to break things down in a non-intimidating way to show meaningful ways on how to get better fuel 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 x.xxx gallons (in the US) to get MPG. If you want to be very accurate 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 had some tanks as low as 19.6 MPG. Since I first wrote this thread she’s had a Jetta Wagon, a Passat Wagon, then a couple of different Mercedes Bluetecs. She’s become quite adept at calculating mileage too.

This all brings us to:
Cascade German’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 90-100% 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 the lowest cetane numbers in your tank (see stations with 40 below). 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 low quality fuel run an additive. I personally like Liquimoly Super Diesel Addtiive as well as Stanadyne. There are lots of write-ups 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 Loves at $4.25/gallon, and 45 MPG from Chevron/BP at $4.49/gallon, you are paying $.10625/mile with Loves, 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.
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 costs you fuel to build back 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 ran ENKEI RPF1 wheels which weigh 13.5 lbs (16″). The cost isn’t worth it for fuel savings, but I liked how they look! 18″ R32 wheels are around 27 lbs and will kill your economy.
5a) Taller 5th gears will lower revs, decrease cabin noise, decrease wear and tear, and make things a lot more comfortable in the cabin. .681 & .658 are our most common gears for TDI 5-speeds.
6) Get a performance chip–Tunezilla tunes are a great choice. 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) Wuzetem nozzles are modeled after Bosch, they are made in Poland using Italian steel. They are balanced and flow tested at the factory and are the closest thing we have found to factory Bosch nozzles in quality. ~($200-250)
8) Downpipe — Breathes better, gave me ~2 MPG, but it helped. (~$250-400 again depending on model). On the common rail 2009+ cars off road downpipes with aa stage 2 tune will average a 5-8 MPG improvement.
9) Larger turbo–again better breathing leads to better economy. Lower EGT’s, which is especially helpful for swaps into heavier vehicles or when towing. ($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!
-Aaron

***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 us, and we 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)