tips for fuel economy

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
I've put this together in an effort to help some folks diagnose what may be a loss of fuel economy (MPGs) with their TDIs. Keep in mind, many of these items can work against your car in concert to add up to a sizeable increase in fuel consumption over time, so please don't dismiss any one item because it may be just one small part of the puzzle, but an important part nonetheless! :)

Tires: this goes beyond simply air pressure, although that is an important part. Tread design is another, as well as the proper size and load rating. When in doubt, look at your car's tire information placard. It will have the proper size, load, and speed rating. Going from the proper 91 load to an 89 (an all too common mistake) can take a 1 MPG hit all by itself over the same model tire. Low Rolling Resistance (LRR) tires are becoming more popular, and are usually marketed as such. Still, keeping the pressure up, and the rating correct, is very important.

Alignment: if the alignment of the car is off, the tires can 'scrub' as they roll down the road. This causes excess friction and drag, which causes the engine to have to work harder. Checking the alignment with proper equipment is the only way to be sure everything is in specification. Worn bushings and steering components can cause the alignment to be out.

Trim pieces and shields: the car was designed to be both slick on the top AND the bottom. Missing shields under the car can not only make the engine take longer to reach operating temperature, they can also cause extra wind resistance when travelling down the road, and the faster you go, the worse it becomes. Missing grill inserts, missing lower splash shields, missing/damaged fender liners, can all contribute to this problem.

Thermostat: if the engine cannot reach proper operating temperature as quickly as possible and maintain it, it will cause more fuel to be used. Don't assume the gauge (or light in the New Beetle and latest Jetta sedan) is enough to tell you the engine coolant is warm enough. The only sure way to know is with a scan tool and watching the coolant temp data. Thermostats don't last forever, and one that cannot do its job properly needs to be replaced. If it gets really bad, the engine controller will flag a fault, however it has to be pretty bad before that happens. Also note that on many TDIs, the coolant temp sensors are notorious for going bad, so you may need to verify both sides (the ECU side and the Instrument side) is working on cars equipped with the 4-pin tandem CTS (specifically, late ALH, BEW, and BHW cars).

Timing: Both the VE TDI and the PD TDI are sensitive to timing. Just a few degrees can make a substantial difference. If the timing belt was installed wrong, your timing will be off. Period. While there is some sliding scale here, as some timing settings favor power over economy, keep this in mind when you set the timing after the belt is installed.

Air cleaner/air flow sensor (MAF): these items need to be in proper condition, and work in conjunction with the Exhaust Gas Recirculation (EGR) for proper engine function. A little bit off, or dirty, or poor quality/fitment can cause some adverse performance.

Lambda (oxygen) sensor (PD only): these can degrade and cause a slow response from the ECU in a similar (but not identical) fashion that a gasoline fueled car can, and can cause some loss of fuel mileage on PDs.

Intake/EGR clogging: while not the issue it once was, due to ULSD fuel, it is still something that should be checked for, especially on VE cars. This can cause a loss of power overall, and call for excessive fuel use since the air the engine needs to run cannot get in properly.

Brakes: many Volkswagens, especially A4 platform cars, have chronic stuck parking brake cables. This causes the rear calipers to drag, and your torquey diesel won't know it... it 'll just eat more fuel to move the car down the road. Also, brake pad perches can rust up, and cause the pads to sieze in their spots, dragging the brakes.

turbocharger: the "T" in "TDI" can't work properly if there is a vacuum/pressure leak, binding VNT/wastegate actuator, etc. While a fault will be flagged if it gets really bad, low boost can slowly creep up and rob you of both power and fuel economy gradually without you even knowing. Again, a scan tool checking requested and actual boost can help check the condition of your turbocharger system.

Driving style: we hear this all too often here, but it bears repeating here. Driving the car too easy for too long can really mess things up in the MPG department. Keeping the pipes clean, by occasional spirited driving, can help to keep the EGR clean, the intake clean, the intercooler clean, the breather system functioning properly, and the turbocharger working correctly, in addition to keep the catalyst and (where equipped) Diesel Particle Filter (DPF) clean and in good working order. A good test on VE and PD cars is to do a floorboarding rolling start (once the engine is warm) and see if it belches out a cloud of black smoke. A healthy, happy TDI, even a mildly modded one, should NOT do this. If it does, and it goes away after doing this a few times, you know you were driving it too easy for too long. Some folks call this an 'Italian tune up'. Whatever you want to call it, it works.

Excess weight: we can call this a minor one, but let's face it, dragging 50 pounds of tools, a stack of bricks, your entire CD collection, your golf clubs, the collected works of Charles Dickens, and 70 bottles of water around in your car is not really necessary.

Hopefully some of the above listed items can help you track down a possible loss of fuel economy! :)
 
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TomJD

Veteran Member
Joined
Jul 9, 2010
Location
St. Louis
TDI
2000 Jetta TDI GLS, 2015 Golf TDI
Another helpful contribution to the TDIclub. Thanks Brian!
 

burpod

teh stallionz!!1
Joined
Nov 27, 2004
Location
cape cod, ma
TDI
82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
ride home for helga
amidst dark night
it rains
mfa shows low mpg
 

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
ScanGaugeII is quite widely used.
 

Sevenjays

Well-known member
Joined
May 7, 2009
Location
Yuba City, California
TDI
2004 Jetta
Slowing down a bit has helped me. I was at 38mpg going 72mph. Slowed to 68 or 69 and I'm above 40mpg now. I just started setting the cruise to 65mph. We'll see what that does. I would really like to average 45mpg. I'm putting most of the other suggestions into practice already.

Thanks for the thread and ideas.

BTW, at 25,000 miles a year and $4.00 a gallon fuel, 1 mpg increase is about $55/year savings. Hmmm, $200 every 100,000 miles is almost the parts kit for my timing belt change!
 

Billion003

Veteran Member
Joined
Jul 19, 2011
Location
Birmingham, Alabama
TDI
2011 Golf
I keep all the excess trunk netting and "stuff" out of my car. Also, no one ever rides in my back seat. I'm looking to take the back seat head rests out.
 

PDX_TDI

Well-known member
Joined
Jun 27, 2004
Location
Beaverton, Oregon
TDI
2013 JETTA w/ PREMIUM PKG
confused about driving car too easy

does "driving the car too easy' mean driving in 5th gear in city driving? I just got 407 miles per tank this last time, and noticed thats the most ive gotten lately (I did just change the timing belt)....

One diesel mechanic told me its good to drive the TDI's above 2000 rpm always.....driving it under, wont give you good mpg.......

is that true?
 

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
...
One diesel mechanic told me its good to drive the TDI's above 2000 rpm always.....driving it under, wont give you good mpg.......

is that true?
'always'? Nope. However it IS good to drive it over 2000 reasonably frequently (and occasionally over 3500) - you need to get the turbo spinning to clear off the coke. What the TDI seems to like best is a bit of variety. It's OK to baby the engine as long as you also thrash it sometimes too. But if you only baby it, or only thrash it, you will end up with problems & reduced performance.
 
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allana13

Active member
Joined
Jan 27, 2011
Location
England
TDI
VW Golf
That is handy information Mike.

I was under the impression drive the TDI between 1500 and 2000 rpm to achive max economy.

BTW how did you manage to get 72 avg MPG on your Audi A2 ?
 

lilspoon

Active member
Joined
Feb 5, 2012
Location
Louisville, KY
TDI
2004 jetta
Do they make guage pods to monitor boost and fuel pressure for these cars?
Just switched from cummins diesels over to the tdi and have been reading around this site for two days. Alot for me to learn as a pick up my 2004 jetta in two weeks.
 

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
That is handy information Mike.
I was under the impression drive the TDI between 1500 and 2000 rpm to achive max economy.
BTW how did you manage to get 72 avg MPG on your Audi A2 ?

'Reasonably frequently' is very different from 'always' :) They can mean virtually the opposite things in terms of the overall time spent at different RPMs. The point is that you need to hit all parts of the rev range SOMETIMES. It doesn't mean that you have to keep the revs high all the time, or even for a significant fraction of time.

I keep the revs low most of the time, which can mean near 1000 in a 30 zone. But it hits 2100 (=60mph) or so every day on the highway part of my journey (70%) which is enough to keep the car decoked, and once in a while I thrash it anyway (push it all the way up to the red line at 100% throttle. But that might be once in one or two months, not even once per tank).

The A2 is relatively low geared compared to my old Passat. I used to have to red-line it more frequently (once every one or two tanks) to keep it decoked, simply because I was usually under 2000 when I was highway cruising. However, when I started pulse&glide instead of steady driving, that was enough to blow the cobwebs out on it's own.

Regarding my average MPG of 72mpg, if you notice that's UK mpg not US mpg. In US terms that's about 61 or so. It's a fairly easy target on the A2 (you'll see back-to-back 75mpg tanks during summer in my fuelly log).

It was very much harder reaching 70+ MPGuk on the Passat, although I did manage it back-to-back several times with a great deal of hypermiling effort.

I don't bother with the hypermiling on the A2. Both cars had basically the same engine (PD TDI), but the A2 has 3 cylinders & the Passat had 4, and a massive difference in weight due to the aluminium body of the A2. Hence 25% less engine resistance on the A2, versus longer glide time on the Passat due to the greater momentum. Overall the benefit of P&G is less now, whereas it was vital on the Passat.
 
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whitevanman

Veteran Member
Joined
Jun 25, 2011
Location
soham
TDI
passat 110 afn
Slowing down a bit has helped me. I was at 38mpg going 72mph. Slowed to 68 or 69 and I'm above 40mpg now. I just started setting the cruise to 65mph. We'll see what that does. I would really like to average 45mpg. I'm putting most of the other suggestions into practice already.

Thanks for the thread and ideas.

BTW, at 25,000 miles a year and $4.00 a gallon fuel, 1 mpg increase is about $55/year savings. Hmmm, $200 every 100,000 miles is almost the parts kit for my timing belt change!
40mpg is terrible for a 1.9 tdi.
 

JettersTDI

Veteran Member
Joined
Oct 5, 2011
Location
California
TDI
2012 Jetta TDI
'Reasonably frequently' is very different from 'always' :) They can mean virtually the opposite things in terms of the overall time spent at different RPMs. The point is that you need to hit all parts of the rev range SOMETIMES. It doesn't mean that you have to keep the revs high all the time, or even for a significant fraction of time.

I keep the revs low most of the time, which can mean near 1000 in a 30 zone. But it hits 2100 (=60mph) or so every day on the highway part of my journey (70%) which is enough to keep the car decoked, and once in a while I thrash it anyway (push it all the way up to the red line at 100% throttle. But that might be once in one or two months, not even once per tank).

The A2 is relatively low geared compared to my old Passat. I used to have to red-line it more frequently (once every one or two tanks) to keep it decoked, simply because I was usually under 2000 when I was highway cruising. However, when I started pulse&glide instead of steady driving, that was enough to blow the cobwebs out on it's own.

Regarding my average MPG of 72mpg, if you notice that's UK mpg not US mpg. In US terms that's about 61 or so. It's a fairly easy target on the A2 (you'll see back-to-back 75mpg tanks during summer in my fuelly log).

It was very much harder reaching 70+ MPGuk on the Passat, although I did manage it back-to-back several times with a great deal of hypermiling effort.

I don't bother with the hypermiling on the A2. Both cars had basically the same engine (PD TDI), but the A2 has 3 cylinders & the Passat had 4, and a massive difference in weight due to the aluminium body of the A2. Hence 25% less engine resistance on the A2, versus longer glide time on the Passat due to the greater momentum. Overall the benefit of P&G is less now, whereas it was vital on the Passat.
That's impressive fuel economy.

But according to this guy, driving the TDi to get the best possible mpg is NOT fun, which means driving slower or at the posted limit.

PLEASE do not drive below the speed limit! Some folks like to get where they're going in a reasonable amount of time. If you wanted to drive like that you should have bought a Prius. Driving should be fun and if you're driving like an old woman while you have one eye on the MFD trying to maximize your MPG, you're not having fun and neither are the people in the line of cars behind you.
 

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
...
But according to this guy, driving the TDi to get the best possible mpg is NOT fun, which means driving slower or at the posted limit.
Hmm, well, different people find different things fun. I like to try to beat my own mpg 'high scores'.

And his comments don't really match up with reality - why on earth would there need to be a queue behind someone on a multilane road with european-style lane rules? It's easy to handle traffic with wildly different speeds if the lane discipline rules are written with that in mind (overtaking lanes are for overtaking, not absent-mindedly cruising). If people have passed their test, they should be capable of these simple driving tasks such as when to change lane & how to use an overtaking lane.
 
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allana13

Active member
Joined
Jan 27, 2011
Location
England
TDI
VW Golf
Mike can you please provide some tips

I have a MK4 Golf Estate 130 Bhp TDI

The max i have achived it 54mpg
 

whitevanman

Veteran Member
Joined
Jun 25, 2011
Location
soham
TDI
passat 110 afn
Mike can you please provide some tips

I have a MK4 Golf Estate 130 Bhp TDI

The max i have achived it 54mpg
Well I can start. service the car, flush the coolant do all the coolant sensors,thermostat and fuel system cleaner.

you should be getting at least 47 mpg after this:rolleyes:
 

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
I tried to write a detailed reply via my phone but it was lost. So I hope you forgive this short one.

Read the vw leaflet in my signature, it covers 90% of it, I will add more to this post tomorrow when I am able to.
 

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
I'm at a proper computer now :) This is an adapted version of something I posted on a different forum:


Note that since the weather is now subzero, the good tanks from summer are unlikely to be repeated until next may or so when the temperatures recover.

Here's the full list of techniques I use - the really important ones are in bold.

* The single most important thing is to keep your motorway cruising speed down to reduce aero drag. I usually stick to 60mph (often I am pulse&gliding between 55 and 60 where traffic, terrain & wind direction permits).
* Make sure the car is in good condition (the correct oil, clean filters, brakes not binding, etc).
* Tyres @ high pressure - I use 44/46 psi, but keep an eye on the centre wear since cheapo tyres will bulge & wear unevenly if at this pressure. Good tyres can handle the pressure fine. The tyres should never be allowed to drop below their proper pressure.
* Climate control & heater off unless absolutely essential (e.g., if it is near freezing you should have the heater on). But turn on the climate control briefly once per tank, after the engine has fully warmed up. This keeps the seals good.
* Keep windows shut above 35mph (not really relevant at the moment since they wouldn't be open in the first place!!!)
* Keep RPM low (but only when engine load is also low). When I'm going at a steady 30 on the flat I'm in 5th at around 1000 rpm. If you need to slow down / speed up / go up an incline you will need to drop a gear or two otherwise you will be overloading ('lugging') the engine. As stated elsewhere you will also need to thrash the car sometimes in order to clean out the coke. Also be aware that low-rpm/high-load will stress your clutch & transmission, so don't forget to change down using the throttle.
* Be aware of wind speed & direction and change your cruising speed appropriately (it affects aero drag). You can go faster with a tailwind but drop your cruising speed if there is a headwind.
* Keep an eye on engine temperature, be very gentle until it was warmed up properly. This can take a long time in the winter. If you have the MFD or a scangauge you'll see that fuel efficiency is terrible until the engine is hot.
* Keep the audio off (so you can hear the engine)
* Leave lots of space between you and the car in front (so you don't need to brake unnecessarily). I'm usually about 3 seconds behind. Some people draft to get better MPG, but this is foolish - you will write off your car sooner or later if you do that.
* Be aware of what is around you at all times (including behind), again so you don't need to brake unnecessarily
* Drive with a steady engine load (allowing RPM & speed to drift)
* Coasting in neutral with engine on - I do this as part of pulse & glide, but only over 35mph or so. Once you are at 30 or below there is no advantage.
* Coasting in gear (when you need to slow down gently, for example down a hill, or towards red lights)
* Drive as if your brake pads were made of platinum :) Every time you touch your brakes unnecessarily you waste fuel.
* Pulse & Glide (40-50mph range)
* High Speed Pulse & Glide (55-60 mph range). Always keep track of other traffic when using P&G, you don't want to irritate other drivers, and there is nothing more irritating than being stuck behind a P&Ging driver.
* Park in a high spot if you can (so when you start, gravity helps you get moving)
* Face-Out Parking so that you don't have to reverse when your engine is cold
* When it is raining, avoid the grooves in the road where the heavy vehicles have worn it out since water causes massive rolling resistance
* Use Shank's pony or a bike if your journey is short
* Avoid traffic jams, cold weather, passengers, rain, wind and driving in the dark. OK, you can't really avoid these, but be aware that they will kill your MPG.

The pulse & glide techniques only have a minimal effect on the MPG of the A2, but used to have a big effect on my old Passat. The difference is that the engine resistance of the A2 is already less due to the 3 cylinders, and also that the A2 is much lighter than the Passat (hence, the Passat would glide better because it had more momentum, and saved more fuel due to the idle making more of a difference).

Some means of knowing trip & instantaneous MPG is extremely useful. The MFD (DIS) was very useful on my old Passat. It allows you to keep track of the MPG for each journey and work out why it was good (or bad) ... for example, I used to be able to tell wind speed & direction from the effect on trip MPG as I drove.

Wheels & tyres: Avoid big rims with wide tyres, tall & narrow tyres give better MPG. Low rolling resistance (LRR) tyres also help.

In terms of mods, I have remapped, installed the 1.2TDI aerodynamic components, and scangauge. Be aware that these modifications will never repay their cost. Being realistic, it's purely for vanity not value for money. Cruise Control is OK MPG-wise on the flat, but turn it off for hills.


The other thing you need to consider is your journey - if you ever do short trips (a mile to the shops or whatever), this will really knock down your tank average. Walk or cycle instead. The car only really starts to get efficient after the engine has fully warmed up (which can be anywhere from 3 miles to 15 miles depending on the weather).

Similarly, city driving will also really push down your MPG. Every time you stop & have to get back up to speed, you are losing fuel.

If your car is new, forget all the above. You should be concentrating on running it in properly (if you always baby it while it is running in, then you will not get a good seal on the piston rings - give it a workout throughout the rev range once in a while, once it is fully up to temperature).

If you have a car with a Diesel Particulate Filter (DPF, > 2005 or so), you also have to sometimes drive it hard enough & long enough to regenerate the DPF, at least once per tank but twice is better. This is extremely important for city drivers, or drivers who only usually do short distances. Otherwise it will clag up quickly & cost you a great deal if you are in the UK or Europe. US drivers usually have it covered under manufacturer warranty so have less to worry about.
 
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