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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old February 9th, 2012, 07:06   #31
JettersTDI
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Can't get any more detailed than that. Thanks for your input.
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Old February 9th, 2012, 08:48   #32
allana13
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Thatís is very informative Mike

Many thanks for that.

Couple of questions What is Pulse and Gliding a bit more detail on that please.

Can we have 44/46 PSI without affecting the tyre? I have good years on mine. I am looking to chage them to all weather tyres. Any recommendation.
I have the standard VW Sports Alloys on MK4 Golfs

Thanks



Quote:
Originally Posted by MikeMars View Post
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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Old February 9th, 2012, 09:32   #33
MikeMars
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Quote:
Originally Posted by allana13 View Post
That’s is very informative Mike

Many thanks for that.

Couple of questions What is Pulse and Gliding a bit more detail on that please.
...
Basically it is a technique to reduce engine resistance briefly.

Pick your target speed range (for example, 40 to 50)
Pulse - accellerate up to 50
Glide - First check behind you, if it is clear, drop the car into neutral, and coast (with the engine still running) until your speed has dropped down to 40.
Repeat.

It doesn't work up long hills, into a strong headwind, high speeds (70 or over) or low speeds (under 30), but it works nicely downhill or with a tailwind. The perfect scenario is when you have a series of very small hills / undulations - power up the hill, and glide down the other side. It does work on the flat, but that takes more effort.

It is also not recommended if you have passengers, or vehicles following behind, because they will become irate quite quickly. The point of this is to reduce the average RPM (by means of being in idle for a period), and hence reduce the energy lost by friction within the engine.

Take a look at Vekke's videos (sticky post at the top of this forum), he demonstrates P&G although accellerates harder than I do (he likes 100% throttle, I prefer about 50%). I don't know which is better, these cars seem to work well either way. Theoretically about 75%-90% should work best according to the BSFC chart, but it can be hard to interpret the chart in terms of real driving conditions. He also explains many of the other driving tips well.

Quote:

Can we have 44/46 PSI without affecting the tyre?...
Regarding the PSI, pump it up to your target pressure, then hold a ruler or other straight edge against the tyre contact surface. If it has bowed out, then you have to run it nearer the standard pressure. However, if it is still as flat as it was before the pressure was increased, then the tyre is good for that pressure. You'll feel much more road contact, and it should be more stable around corners, but it will give you a harsher & noisier ride (the recommended pressure is a compromise between different factors such as comfort, noise, mpg, cornering, & stopping distance. We are sacrificing some of the comfort for MPG).

I like to use Michellin Energy Saver tyres, they hold their shape well, last a long time, and roll well. But I think they are summer tyres not all-weather tyres. If you change your tyres for economy reasons alone, it only makes financial sense once your originals have worn out.
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Audi A2 TDi 1.4*, 6M/0.588, mild aero mods, 103hp remap (* 3 pot version of 1.9PD)
Y2000 Passat TDi 115 PD RETIRED, M5, Best 75MPGuk, usually 60-70. 900m clubx7. 1000 mile clubx3.
VW Fuel saving tips

Last edited by MikeMars; February 9th, 2012 at 10:06.
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Old February 9th, 2012, 10:03   #34
allana13
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Thanks very much for the Info Mike.

Guess its best to have 2 sets of tyres then, Winters & summers.
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Old February 10th, 2012, 08:03   #35
Deftones
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My car doesnt have a temp gauge. I thought that was weird.
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Old February 10th, 2012, 13:38   #36
oilhammer
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Quote:
Originally Posted by Deftones View Post
My car doesnt have a temp gauge. I thought that was weird.
Not really. Even cars that do, don't generally have a "real" gauge, including all modern VAG products. That is why they can use the exact same sender.
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Old February 21st, 2012, 11:19   #37
whitevanman
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Quote:
Originally Posted by MikeMars View Post
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.
Sorry but Ive always been taught that a car idleing uses more fuel than a car under load? And If i was to give the car a good thrashing to put it in second gear would that be bad for it (considering ultra high mileage)
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Old February 21st, 2012, 11:31   #38
MikeMars
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Sorry but I've always been taught that a car idleing uses more fuel than a car under load?
I'm not sure what part of my post you're referring to here. A stationary car will have zero mpg when idling of course (since it is not going anywhere).

I can't think of a case where a moving car in neutral & idle would be using more fuel at that moment in time than a car which is under a significant positive load at the same speed (i.e., accelerating). I'm probably misunderstanding your question.

Petrol vehicles have a very inefficient idle, but it's much more efficient on a diesel (one of the main reasons why real-world MPG is much better on diesels than petrols).

If you're referring to the neutral vs. underrun (negative load) debate, then the answer is that it depends on the circumstances - you need to use the right technique at the right time.

If you are referring to the BSFC chart (efficiency varying by load & by rpm), then you need to interpret the chart in terms of the overall dynamic picture, not just the instantaneous bsfc.

Quote:
And If i was to give the car a good thrashing to put it in second gear would that be bad for it (considering ultra high mileage)
It's fine as long as a) you keep it under the red line, and b) the engine has fully warmed up to operating temperature. If you thrash it while the engine is cold that is very bad.


PS it may be a good idea to shorten the quoted part of your post since my original post was rather long & it takes up a lot of space. If you cut it down so that only the relevant parts of my post are shown, it will make things easier to read & understand.
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Y2000 Passat TDi 115 PD RETIRED, M5, Best 75MPGuk, usually 60-70. 900m clubx7. 1000 mile clubx3.
VW Fuel saving tips

Last edited by MikeMars; February 21st, 2012 at 12:56.
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Old February 22nd, 2012, 04:55   #39
allana13
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Mike i have followed what you have suggested and have achieved nearly 67mpg at 1 stage. I also did manage to get 60mpg on a average

Thanks
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Old February 22nd, 2012, 07:10   #40
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That's great :-)
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Y2000 Passat TDi 115 PD RETIRED, M5, Best 75MPGuk, usually 60-70. 900m clubx7. 1000 mile clubx3.
VW Fuel saving tips
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Old February 22nd, 2012, 19:23   #41
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I don't really want to make driving any more scientific than it needs to be, for the most part I'm in the drive-it-like-you-stole-it camp, but what would be considered "thrashing" the car in terms of RPMs -especially when the car is warming up? I hear people say to ease into each gear but what does that mean? When it's warming up, I typically shift a little above 2000 just because I like to hear the turbo *whoosh*, but is that a no-no? On the other hand shifting too soon (around 1400rpm or so), at least for me, causes the engine to lug for a bit. Ultimately which is worse for the engine, the "thrashing" or the lugging? I got a TDI over a hybrid because I can actually drive the damn car and still get pretty great fuel economy, but I don't want to do so in a way thats going to prematurely run it into the ground.

Also how does P&G affect the lifespan of the components?
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Old February 23rd, 2012, 04:34   #42
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I try and keep the RPMs over 2500 during warmup. That keeps the afterglow OFF. The plugs cycle on and off at 2500 RPM, or in the case of the 2002+ cars, the control unit duty cycles them up at 2500 RPM. In either case, that constant on/off of the plugs is what shortens their life. And of course never let it sit and idle after a cold start.

I'm lucky, because I have my car covered in the morning, so no scraping ice or anything, it is backed in its spot. I literally start up, drive off, 1-2-3-4 and I am doing 60. Hold 60 in 4th (above 2500 RPM) for that first couple miles on two-lane black top until I merge on to the interstate... then hammer down and into 5th and 80+ for 40 minutes. Probably why my cars last so long. They get up to temp very quickly, and are mostly hwy miles.
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Old February 23rd, 2012, 07:35   #43
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Quote:
Originally Posted by Forza91 View Post
...
Also how does P&G affect the lifespan of the components?
It's very hard (brutal) on the clutch & transmission if you are doing 'engine-off' coasting. However that's not a good idea anyway due to the loss of vacuum causing the brake & steering to become hard.

'Engine-on' coasting is more benign, but does involve many more gear changes than otherwise, so a degree of extra wear is to be expected.

I personally would keep both load & rpm low until the engine has heated up properly. The engine oil only becomes fluid when the engine is hot.

Once the engine is hot, then you can push it up to the red line as often as you want (but for the purposes of de-coking you only need to do it once a tank or two). Note that revving with no load isn't particularly useful, you need to be putting the engine under load (i.e., up a hill in 4th).
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Audi A2 TDi 1.4*, 6M/0.588, mild aero mods, 103hp remap (* 3 pot version of 1.9PD)
Y2000 Passat TDi 115 PD RETIRED, M5, Best 75MPGuk, usually 60-70. 900m clubx7. 1000 mile clubx3.
VW Fuel saving tips

Last edited by MikeMars; February 23rd, 2012 at 07:47.
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Old February 27th, 2012, 11:53   #44
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Quote:
Originally Posted by MikeMars View Post

.......
Once the engine is hot, then you can push it up to the red line as often as you want (but for the purposes of de-coking you only need to do it once a tank or two). Note that revving with no load isn't particularly useful, you need to be putting the engine under load (i.e., up a hill in 4th).
Or you could just drive at 50, drop down to 3rd and go for it all the way to 75/80, the car blow all the crap out
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Old March 5th, 2012, 18:57   #45
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I was reading the post on fuel economy and it mention something about a Italian tune up.Do you keep doing this until the black smoke quits or just lessons.
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