Driving for better mpg

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
Expectation.
The professional driver achieved 63mpUSg while driving the EPA cycle. This figure is then downgraded by 22% to allow for real life road conditions and less than professional drivers. The published figure according to the EPA is 49mpUSg.

Drive your own road.
Drive responsibly, share the road.
Drive purposefully, at your own speed.
Select your route to avoid stop streets, slow roads, and fast highways.
Opt to drive on roads with good road surfaces.
Opt to drive at a time of day that avoids “rush hour” or traffic build ups.
Know what the speed limit is, and drive appropriately.
Do not drive in “the pack”.
Do not hinder other road users, let them pass.
Do not let other road users intimidate you.
Do not let another road user tailgate you, drive the speed limit.
Do not tailgate, use the 2 second rule.

Gears.
Use 5th gear whenever you can. Use the highest gear possible at all times.
Don’t be afraid to change gear. Get used to it. Change up, change down. The best time to change gear, is the first time you think about it.
At 40mph the engine uses 20% less fuel in 5th than in 4th to produce the 6 hp needed to keep the car moving on a flat road. But, that is getting close to the lugging condition, so be prepared to change gears should it be necessary. In fact the engine uses 20% more fuel to produce the same HP at any speed in 4th than in 5th. Clearly 5th gear is the best gear for mpg’s.

Brakes.
A good way to convert fuel into heat and dust. Avoid using them. Adjust the speed of the car using your right foot only. This means you have to read the road ahead, and drive smoothly. Use the brakes only: at the end of your journey; at stop streets; at red lights; for policemen; pedestrians; and idiots; Avoid all other uses of the brake pedal.
Excessive use of the brakes costs you in fuel, in brake pads, in rotors, and in time to get these items replaced.

Cruise control.
Use the cruise, it does a pretty good job, except when driving downhill. Get used to using the cruise control as part of your driving technique, applying it when appropriate.

Right foot.
The TDI engine’s fuel efficiency, (converting the BTUs in the fuel into HP at the wheels) varies from a high of 45% to a low of 12%. The 45% occurs with a heavy right foot, the 12% occurs with a light right foot.
At 1750 rpm the range is 45% to 15%. At 3500 rpm the range is 36% to 12%.
Therefore: use a heavy right foot at low rpm, whenever you can.
To get better mpg’s you need to use the engines best fuel efficiency. The TDI is fuel efficient when you use a heavy right foot. It is fuel inefficient when using a light right foot.
Use the “some or none” technique, ie a heavy right foot or no right foot. - Drive with purpose. Romp up hill, and coast down hill.

RPM.
Keep the RPM down. But, be careful to not lug the engine, which might occur below 1300 rpm.
Lugging is a condition where the power required is more than the power available from the engine. Typically in a gasser this is stated as “keep the revs above 2000” Most 2litre gassers have 30hp available at 2000 rpm. The TDI has 30hp available at 1300rpm. Therefore the equivalent statement for the TDI is “keep the revs above 1300 rpm” to avoid lugging.
When slowing down keep the car in 5th until the rpm’s are less than 1000 rpm, then change down, as this will minimize the engine braking effects. When driving on a flat road, with only the driver in the car it will pull in 5th from 1100 rpm without lugging, and on a downhill even at lower rpm. Get to know your cars capability in this rpm range.
But, don’t forget to exercise the car from time to time through the whole rev range. Say once a week, when accelerating on a highway on ramp, hold second gear and stomp on the go faster pedal and let the rpm go through to the top. It blows out a whole bunch of crud, and keeps the engine sweet. The engine responds well to a touch of variety.
By the way, the 90HP TDI can produce 20HP at 1000 rpm, 30HP at 1300, 41HP at 1500, 56HP at 1900, 71HP at 2500, 82HP at 3000, 87HP at 3500.

Cold Start.
Observing the mpgs I return when I make 1 journey of 200 miles, vs 10 journeys of 20 miles, indicates to me that there is a cold start penalty equivalent to 3 miles. I think this cold start process takes place over the first 10 miles. The temp gauge shows the engine coolant is up to temp in 2-5 miles, but, I am of the opinion that this process is not complete at that point, there’s more too it. For the first 10 miles of a journey the TDI engine (not just the coolant) has to get to operating temperature, as does the gearbox, wheel bearings, tires, brakes, etc etc. It takes +/- 10miles, regardless of conditions, or how you drive. The only thing that can be done is to reduce the losses, ie keep them closer to 20% rather than 30% (2milesworth rather than 3milesworth). In other words drive careful during the first 10 miles. Do not blast off from a cold start, or you will experience a cold start penalty that is larger.
The glow plugs operate to help warm up the car, but only if you keep the rpm below 2200. If you exceed 2400rpm the glow plugs shut off. So keep it below 2200 rpm til the temp guage is off the bottom three marks.
I have wondered about the TDI heater or Zerostart device that keeps warm water in the radiator, and how this might help to reduce the Cold Start Penalty.

Driving off.
Get in the car, fasten seat belt, start the engine, and drive off.
Do not let the engine idle, to “warm up”. The engine warms up quicker when its under load, and the mpg’s benefit because you are using the fuel to go somewhere. The lube oil in the engine is up to pressure and distributed throughout the engine in the first 5 seconds or less.

Getting up to speed.
5th gear is the economy gear. Your goal is to get into 5th gear as fast as is reasonably possible. Use first gear to get the car rolling. Within 4 cars lengths you should have gone through 1st, and 2nd, and have engaged 3rd. Do as much of your driving as you can in 5th. You will be changing gear below 2000 rpm. So flip your way through those gears in the 1300-2000 rpm range. Target to get into 5th at 40mph and 1350rpm on a flat road. Higher rpm of course on an uphill, lower on a downhill.
Sometimes you’ll need to pull away harder, do it pedal to the metal in the highest gear possible.

Speed.
The optimal speed, on a flat road, is somewhere around 40mph. (+/- 1300 rpm in 5th) The higher the speed the more effort it takes to move the air out of the way. (As airspeed doubles, the force of the wind quadruples, any yachtsman will tell you that.) The optimal speed is not 30mph because of the engine’s lousy fuel efficiency at real low rpm.
However this “optimal speed” is often not possible because it is too fast (legally) for an urban road speed limit, and too slow (sensibly) for a highway.
Travel at a speed fast enough to allow the continual use of 5th gear, and as slow as road conditions permit. Be careful, do not hinder other road users.
Tailgating a big truck can give significant reductions in wind resistance but is really not sensible. Keep your distance, observe the 2 second rule, you will get some drafting effect at 60 mph and faster. Less than 50mph, its just not worth it, anyway.
As a rule of thumb these numbers are very possible:
40mph = 80mpUSgallon
50mph = 70mpUSgallon
60mph = 60mpUSgallon
70mph = 50mpUSgallon
80mph = 40mpUSgallon

Slowing down.
Don’t use the brakes. The brakes are very good at stopping the vehicle, and in converting fuel into heat and dust. Avoid using them for slowing down.
Over-run is the method of choice. It is the safest. At low speeds the engine braking effect is minimal. In some locales coasting and freewheeling are illegal.
Over-run is where the car is in gear, no right foot, no brake, the car is traveling along subject to engine braking effects. The engine consumes no fuel.
Coasting is where the car is not in gear, the engine idling, the car is traveling along the road without any engine braking effects, but the engine is consuming fuel to keep it idling.
Free-wheeling, is where the car is not in gear, engine is off. How do you steer? As there is no power steering. And how long will the brakes remain effective for? Not a good idea.
Coasting is of use under certain conditions (>50mph). The amount of fuel used (0.5 litre an hour) may be less than the engine braking effect. It depends on the road conditions. If in doubt use over-run.
When using over-run allow the rpm to drop to 1000 before changing down, as this will minimize the engine braking effect.

Stopped.
Turn the engine off if you think you are going to stand still for more than 10 seconds. No use burning fuel to go nowhere. Restarting the engine uses as much fuel as “10 seconds” worth of idling.

Driving Uphill.
This is where you can operate the engine close to its most efficient, take advantage of it.
Do not take a run at an uphill. Allow the car to slow a little, get into the slow lane, and drive up the hill at a speed such that you can maintain 5th gear, with a heavy right foot.
Example: Taking an 8% uphill at 50 mph will give good results, it will be marginally better mpg’s to take it at 40mph, but at 60mph there is a distinct drop off as you are moving out of the fuel efficiency curve.
This engine is most efficient when asked to make lotsa hp. The more hp, the more efficient, use a heavy right foot, and slowing down allows for a heavier right foot.
Just don’t overdo it and get into a lugging situation. Lugging, and changing down is not good.

Driving Downhill.
Driving the car gently down a hill is a very inefficient use of the engine. This engine converts fuel to power most inefficiently when asked to make a couple of hp only. The difference can be as much as 3 times as much fuel consumed to produce a HP. (Ie 15% efficiency instead of 45% efficiency)
Do not use the cruise when going downhill.
Let the car over-run. Do not use the right foot to maintain speed going down a gentle slope. If the hill is not steep enough for the car to maintain speed, let it slow down, (or knock it out of gear so it will maintain speed – careful, maybe illegal). Do not maintain a light right foot to keep the speed up.
Go into a downhill, adjust the cars speed (faster or slower) so that it can go down the hill with no right foot, and no braking required, and at the bottom of the downhill come out at your desired speed.
Coasting in gear is always preferable for mpg’s when your speed is below 45mph. Above 50mph it may be preferable for mpg’s to coast out of gear (engine is idling, consuming fuel) assuming that you can handle the extra speed without using the brakes. And, assuming its not illegal to coast out of gear in your area. The engine idling consumes, say 0.5 litre per hour, that’s enough fuel for 2.5HP. Above 50mph the engine’s braking effect is more than that. If the road conditions, and traffic are such that you can coast out of gear, then coasting can show a better MPG at speeds above 50 mph. If in doubt over-run, (coast in gear). Then you wont have burnt the fuel just to idle the engine while coasting, that is in case you have to use the brakes.

2 second rule.
Don’t tailgate. Use the 2 second rule. When the vehicle in front of you passes some mark, count; One crocodile, Two crocodile, and then you should pass the same mark. It’s a simple rule to check yourself when driving in traffic, and especially at higher speeds, that you are maintaining a reasonable distance between yourself and the vehicle in front.
In some places people may argue that if they leave a “2 second” gap others will cut–in. That’s got nothing to do with your driving, do not get lured into driving in some one else’s style. Decide on, and stick with, your own driving habit. Can you drive an alternate route, or at a different time of day? Do not drive in the pack, drive your own road.


My numbers? 80,000 miles at an average of 59.5 mpUSg, in my 2002 VW Golf 2 door TDI.
From Jan 15 2002 to 16 November 2005.
P.s. The intake has not clogged, he turbo has not surged, and the car is running real sweet, and strong.

Have fun.:)
 

Ernie Rogers

Veteran Member
Joined
Oct 15, 2001
Location
Pleasant Grove, Utah
TDI
Beetle, 2003, silver
Wow, thanks, gdr,

That should have a special flag on it or something.

I am a little uncomfortable with flooring it below 2000 rpm, it could damage the turbo? (Coincidentally, that's where max efficiency is, pretty close.)

Ernie Rogers
 

Zero10

Veteran Member
Joined
Jan 16, 2004
Location
Calgary, AB
TDI
05 Golf TDI PD, Tiptronic
I adopted rather similar driving methods, and got well below 30mpg in my 05 Golf GLS auto. I went to a very light right-foot, and the first tank like that was 34mpg.
Seems to contradict what you are saying. Perhaps this is due to the automatic transmission?...
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
You will be changing gear below 2000 rpm. So flip your way through those gears in the 1300-2000 rpm range. [/qoute]

Follow that advice and you will do one of two things:

Blow your turbo to kingdom come if you live at high elevations or Completely soot lock your VNT mechanism and kill compression from lack of clean combustion and boost pressures to cycle your compression rings...seen it done TOO many times by people trying to drive for maximum fuel economy!

If you want to lug a motor around driving that way, buy a non-turbo gasser and lug it since you can't hurt anything.

TDI's MUST HAVE BOOST pressure to cycel the VNT, heat up that Catylitic converter and cook the carbon out of the rest of the motor.

Low rpms translate into VERY low fuel pressures, low oil flow under the pistons, low compression pressures which are MANDATORY to keep the rings floating in the lands and sealing properly.

Shifting below 2,000 rpm also places the TDI engines directly at the "Surge Line" for the VNT turbo's compressor, meaning you are causing the engine to run at peak boost pressures that can cause a complete failure of the turbo.

Follow this advice and you will permamntly damage your motor...DON'T DO IT!

Drive your car the way it was intended, keep in mind these engines were designed for driving on the Autobahn NOT for lugging around town in some attempt to get 90mpg...For that they sell a diesel called the "SDI" which does not have a turbo and can be lugged as suggested above.

DB
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
By the way, the 90HP TDI can produce 20HP at 1000 rpm, 30HP at 1300, 41HP at 1500, 56HP at 1900, 71HP at 2500, 82HP at 3000, 87HP at 3500.
Yes it CAN produce that power but it can also produce 30 hp at 2,500 rpm...You are confusing the fact that this engine is NOT a gasser and does not subscribe to stiochiometric fuel ratios. Fuel ratios are dependent on load. The TDI fuel consumbtion graph shows that maximum fuel economy for a TDI occurs at a range of 1800-2100 rpm. In that range fuel economy remains nearly the same. Driving at those rpms places you at or around speeds of 55-60 mph.

My advice is to accelerate rapidly and once up to speed keep the engine at an rpm that places you as close to 2,000 rpm as possible. This puts the engine in it's most efficient fuel consumption range and keeps the engine operating at an rpm that it was designed for.

DB
 

compu_85

Gadget Guy
Joined
Sep 29, 2003
Location
Springfield VA
TDI
... None :S
I have to disagree with your millage numbers. I drive 80 or quicker on the freeway, and get 45 mpgs with biodiesel! :D

-J
 

Muggins

Veteran Member
Joined
Jun 7, 2002
Location
Barrie, Canada
TDI
02 Golf GL 4dr 5spd
gdr703 said:
My numbers? 80,000 miles at an average of 59.5 mpUSg, in my 2002 VW Golf 2 door TDI.
From Jan 15 2002 to 16 November 2005.
P.s. The intake has not clogged, he turbo has not surged, and the car is running real sweet, and strong.

Have fun.:)
Have you ever (or lately) removed the EGR to actually check the intake?

And how do you know the turbo has never surged? Do you have a boost gauge?
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Driving that way more than likely his turbo is jammed up and won't make full boost pressure.

Also cars run this way suffer from lower compression thus lower efficiency in terms of directly effecting fuel economy.

DB
 

tomo366

TDI Lifer, Member #68
Joined
Jun 30, 1997
Location
Kensington, Maryland USA
TDI
2015 Jetta SEL TDI
LOL.....SOS huh Jack???
I can't wait until you slam the vanes of the Turbo on the Passat......
Then I will buy it for 5000 that's the 05 Passat Jack!!
Keep driving them like a grand mom ma..........
 

Bob_Fout

Oil Wanker
Joined
Sep 5, 2004
Location
Indiana
TDI
2003 Jetta - Alaska Green (sold) / 2015 GTI 2.0T
BRUSSELS BELGIAN said:
Just to rain on everyone else's parade, I think gdr703's advice is RIGHT ON!
Driving for absolute best MPG (no matter the effects), yes. Driving for engine health, no.

I get 2 to 3 MPG less now that I drive "like I stole it" compared to when I'd baby it. Big whoop. The car is noticably quicker, and if exercising the engine will keep it running good, I'll keep doing it.

You'll have to save an aweful lot of fuel to defray the cost of an intake cleaning, clean/replace the turbo, and fix low engine compression.
 

Ernie Rogers

Veteran Member
Joined
Oct 15, 2001
Location
Pleasant Grove, Utah
TDI
Beetle, 2003, silver
Thanks, guys, for the great wisdom.

I think it's time for me to blow out my engine, been babying it the last few days. 95% of the time I drive like a grandma (good mileage) and the remainder I drive like a suburbanite late to work.

Now at 107k miles, never cleaned anything, but changing filters and timing belt. I hope to keep it going that way. (Got 69 mpg last trip to Fresno, this Wednesday.)

Thanks again, I really depend on the lessons I get here.

Ernie Rogers
 

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
Muggins said:
Have you ever (or lately) removed the EGR to actually check the intake?

And how do you know the turbo has never surged? Do you have a boost gauge?
Recently a mechanic changed the timing belt, and water pump etc.
His observation, is that its all fine.

Refer to the thread: "Some myths about surge..."
From that thread I understand that it would be known if it ever did surge.
 

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
Drivbiwire said:
You will be changing gear below 2000 rpm. So flip your way through those gears in the 1300-2000 rpm range.

Follow that advice and you will do one of two things:
The latest 66Kw TDI version is characterised by very low smoke emissions and an improved "driveability". The maximum torque, acheived as low as 1900 rpm, has been increased . . . . This allows the customer to shift gears earlier and therefore leads to a further improved economy.

The new MY98 . is equipped with a special VNY turbocharger. . .
At low rpms , higher boost pressures can nevertheless be created by the variable geometry of the VNT.
For the customer this means improved fuel economy and more motoring enjoyment due to a greater torque in all areas of the engine map.

Quotes taken from
Realising Future Trends in Diesel Engine Development.
B Georgi, S Hunkert,J. Liang, and M Willman. - Volkswagen Ag.
Copyright 1997 Society of Automotive Engineers Inc
 
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Khal

Veteran Member
Joined
Dec 31, 2003
Location
Mississauga, Ontario
From my experience I perfer the spirted driving style. I tried the max MPG approach and the car felt sluggish when I did need the oomph to get going. Did not feel perfectly safe when I was not at a gear I could gun it in case I needed the getup and go.

Besides it is so much more fun to use the full range of the motor. Also the tank following my max mpg attempt the car did not get up to 160kph that easily. Later on that tank it got there without a prob and was pulling like a frieght train.

Excercising the turbo is not only good for the turbo, but also for the heart :D
 

Bob_Fout

Oil Wanker
Joined
Sep 5, 2004
Location
Indiana
TDI
2003 Jetta - Alaska Green (sold) / 2015 GTI 2.0T
Khal said:
From my experience I perfer the spirted driving style. I tried the max MPG approach and the car felt sluggish when I did need the oomph to get going. Did not feel perfectly safe when I was not at a gear I could gun it in case I needed the getup and go.

Besides it is so much more fun to use the full range of the motor. Also the tank following my max mpg attempt the car did not get up to 160kph that easily. Later on that tank it got there without a prob and was pulling like a frieght train.

Excercising the turbo is not only good for the turbo, but also for the heart :D
Just make sure it's not bad for the wallet....
 

Khal

Veteran Member
Joined
Dec 31, 2003
Location
Mississauga, Ontario
The difference is not that much when driving around town. The main difference in MPG is the sustained speeds. I can't drive on the 401 in Toronto at any speeds under 120kph and feel safe. 100kph in the right lane = getting cut off like there is no tomorrow. 120kph+ (flow of traffic) in the left lane = nice relaxing drive.

I am happy with 42-44 with 60% highway and of that I spend 50% of the time in first gear in rush hour traffic. The best tank of 54MPG was a trip from Toronto to Montreal and back (Approx 1100kms). Avg speed was around 120kph. Booting around town for about 80kms and some fun runs up Mount Royal :p

My '01 Z24 got 22-26 MPG with the same driving style. I am still way ahead :D
 

rotarykid

Top Post Dawg
Joined
Apr 27, 2003
Location
Piedmont of N.C. & the plains of Colorado
TDI
1997 Passat TDI White,99.5 Blue Jetta TDI
city mpgs can excede highway mpgs

Driving like the poster wrote is on target for how the car was designed to be driven .

Don't let anyone tell you different .

I was around the VWAG engineer that tested the TDI in the US in 94 & 95 , in Colorado . I also have stacks of published test data on the early VGt turbos and how the 1,200 to 1,300 rpm range was what they were shooting for in the design low end rpm range .

If driven properally 2 to 5 mpgs can achieved in city driving over highway speed trips . All mpg numbers below are in my 97 TDI Passat .


I always get higher mpgs in my city driving than on my trips accross the US . I get around 50 mpgUS on trips across the US from Denver CO to Mooresville NC . 70 to 90 mph is my norm , speed limit of 65 to 75 mph over the trip .

While driving around southeastern NC , Oak Island NC I've gotten almost 57 mpgs . Low speed limits 30 to 55 mph max . My normal mpgs are 52 to 55 mpgs running around the area .


I've gotten close to 59 mpgs runnign around Denver CO 20 to 50 mph mostly with short trips of 65 to 70 mph on the intercity freeways . My mpgs are 52 to 55 running around the Denver CO area .


I've gotten mid 50s running around Denver in a 99.5 5spd Jetta TDI .
 

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
My .02 additions: First, I agree with Drivebywire regarding lugging the engine, turbo spikes, carbon, and so on. I can feel the engine lugging if I get into the throttle at under 1800 or so. I think it's OK to drive at these engine speeds, but you should drop down a gear if you want to accelerate quickly.

It's interesting to me that people complain about the VNTs having short lives, but they chip their engines, don't add boostvalves, and then drive like the first post recommends. It's a prescription for disaster. You can see 26 lbs., easy, under these conditions.

If you drive purely to get the best mileage you will pay other prices. My '97 was driven very, very gently for its first 34K by an elderly owner. I rode with him and he rarely got over 1500 RPM. That car ran like crap when I got it. Plugged intake and CAT, and evidence of less than optimal compression. I've been driving it pretty hard and have modded it since I got it (also cleaned out the intake and replaced the CAT) and it's improving. But it took close to $1,000 in repairs to get it back on track.

I usually drive my wagon between 2000 and 3000 RPM. I never stab the throttle, either when accelerating off or after shifts. I always roll into the throttle to make sure the turbo has time to spool up. And I don't hesitate to drive it fast. I've gotten a low of 38 and a high of 50 since I got the car, and I rarely drive at less than 75 on the highway. And my intake was pretty clean at 98K. CAT and turbo are fine.

For me, that's economy. Good mileage plus long component life.
 

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
compu_85 said:
I have to disagree with your millage numbers. I drive 80 or quicker on the freeway, and get 45 mpgs with biodiesel! :D

-J
I believe i get more like:
65 mpg @ 60 mph
55 mpg @ 70 mph, which would be in line with your
45 mpg @ 80 mph

so i agree with your disagreement!:rolleyes:
 

Grinch

Active member
Joined
Apr 9, 2001
Location
Cleveland, Ohio
TDI
2001 Black Jetta TDI
I get 53mpg pretty much all the time. But I also keep it under 60mph for the most part on the highway. Much less stressful having traffic go around me than fighting to get ahead. 2001 Jetta TDI
 

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
Drivbiwire said:
Blow your turbo to kingdom come if you live at high elevations or Completely soot lock your VNT mechanism and kill compression from lack of clean combustion and boost pressures to cycle your compression rings...

Shifting below 2,000 rpm also places the TDI engines directly at the "Surge Line" for the VNT turbo's compressor, meaning you are causing the engine to run at peak boost pressures that can cause a complete failure of the turbo.
Appreciate your concern, but I understand that:

Turbo surge is a condition that might occur if:
You are driving at altitude, say in excess of 2600 metres (8500 feet)
The car is under load: towing a trailer, going uphill, with 5 people on board.
The car is in 5th gear, the engine is idling, 903 rpm, and you punch the go-faster pedal as hard as you can.
If any one of these conditions is missing the TDI will not surge, in an unmodified TDI.

Clogged intakes occur because of a combination of factors, but primarily the soot comes from the EGR which is only open when below 3000 rpm, and when driving with a light right foot. When driving with a heavy right foot, below 3000 rpm the EGR is closed, and clogging is unlikely.

Therefore I think its perfectly OK to drive smoothly, with a heavy right foot. No surge, no lugging, and no clogging.

Isn't that right?
 

greenskeeper

Top Post Dawg
Joined
Mar 10, 2003
Location
USA
TDI
1998 Jetta TDI
My A3 has the old style waste-gated turbo so no vane issues there.

Also I've often wondered how it is possible to over-fuel at low rpm to create "surge" or "lugging" if the entire rpm band is fueled by the ECU which in turn has a "smoke map" built into the program.

I'd believe this if our TDIs were mechanically controlled where you could dump a ton of fuel into the engine at low rpm but not when they are computer controlled.
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Clogged intakes occur because of a combination of factors, but primarily the soot comes from the EGR which is only open when below 3000 rpm, and when driving with a light right foot. When driving with a heavy right foot, below
Wrong. EGR is at MAXIMUM flow at low loads due to "Leaner burning" thus having excess air causing an increase in combustion temperatures leading to higher NOx output. Higher loads ie "Spirited" driving causes the EGR map to reduce the amount of EGR thus reducing the soot injected.

Maximum EGR occurs at idle and low power output...1300 rpm has higher EGR rates than an engine at 2,500rpm and higher loads... If I was at home I'd post the 3D graph showing the corelation of EGR rates and load.

Also low loads causes higher amounts of oil to get passed the compressor seal...Not the best thing for your catalyitic converter!

Again low engine output causes EGR to INCREASE not decrease.

DB
 

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
greenskeeper said:
My A3 has the old style waste-gated turbo so no vane issues there.

Also I've often wondered how it is possible to over-fuel at low rpm to create "surge" or "lugging" if the entire rpm band is fueled by the ECU which in turn has a "smoke map" built into the program.

I'd believe this if our TDIs were mechanically controlled where you could dump a ton of fuel into the engine at low rpm but not when they are computer controlled.
Greenskeeper, I have to think your TDI is an abberation. A wonderful one, but an abberation nonetheless.:D
 

Drivbiwire

Zehntes Jahr der Veteran
Joined
Oct 13, 1998
Location
Boise, Idaho
TDI
2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
greenskeeper said:
My A3 has the old style waste-gated turbo so no vane issues there.

Also I've often wondered how it is possible to over-fuel at low rpm to create "surge" or "lugging" if the entire rpm band is fueled by the ECU which in turn has a "smoke map" built into the program.

I'd believe this if our TDIs were mechanically controlled where you could dump a ton of fuel into the engine at low rpm but not when they are computer controlled.
Valid question for VNT equipped TDI's (pd and ve), up until 1900 rpm give or take the the ECU commands maximum boost from the turbo in terms of vane position. Whether you are at idle or 1900 rpm more the turbo will respond to the gas energy that is available. Realize that gas energy ie power output from the engine in the exhaust is what drives the turbine. Low loads simply do not provide sufficient energy to cause the turbo to create boost pressures that are out of limits for the turbo. Low gas energy also causes very low temperatures within the turbine thus the reason why they clog with soot simply because it is not being burned off and soot eventually restricts the range of motion of the VNT control ring and vane arms.

Back to the surge issue, since the turbo is always commanding maximum boost think of boost control as a reactionary control, the ecu has to see boost pressure before it will command the N75 to reduce it and this is why the turbo can get into surge.

In a stock TDI with absolutely no mods the ECU is programmed to allow boost pressures that approach surge. Obviously when the ECU sees the pressures that could pose potential for surge the N75 responds to the command from the ECU to decrease boost then the N75 reduces the vacuum applied to the VNT actuator, pressure drops, VNT actuator spring retracts the VNT arm and boost begins to drop...notice all the steps there to reduce boost pressure? That is why the VNT is prone to surge, there are multiple steps that have to occur only after the boost pressure is already approaching the surge limit.

One reason to run a turbo so close to surge is emissions. VW needed to keep maximum air in the cylinders for the given amount of fueling that would allow maximum power and minimum smoke output. That fine line is not linear and varies on many variables.

An engine that is run at low loads is essentially running with the VNT in the maximum boost position. Typical of these cars that are lugged/drivne gently/babied/driven for fuel economy (insert whatever applies) is that the ECU eventually and certainly throws a High boost pressure deviation code. What has happened is the lack of cycling of the vanes has allowed soot to jam up the mechanism thus preventing the VNT from returning to the low boost position. FYI everytime you shut the car off the VNT returns to the default low boost position. With frequent short drives and lack of boost or for any of the already mentioned factors the soot builds up to the point that the VNT no longer can move to a position that can prevent overboost thus crossing the line into surge because you have essentially an unregulated turbo with plenty of gas energy to cause it to grenade. The ECU does have a protection for this that being the overboost code, when this is thrown the ECU since it cannot reduce boost reduces gas energy by way of a reduction in maximum Injection Quantity "IQ". This limits the fueling in for a given rpm and load so that the turbo never has sufficient energy to overboost. Since most people who drive for economy never give make enough power to cause overboost they never get the engine code that is until they are climbing a long grade or actually trying to drive at higher than normal speed then whamo engine code or worse blown turbo.

I agree with the higher elevations but what people forget is that compressors and turbines do not prescribe to elevation in terms of feet above Sea Level. What people do not realize is that even if you are at Sea level it is possible to have air density that approaches elevations of 5,000 feet. Using the Standard day as a guide Sea Level is based on a 15C/59F day at Sea Level. Everytime the temperature goes above 15C/59F the elevation that your turbo thinks its at goes up rapidly. Low pressure from bad weather and this again is another factor that increases that altitude factor further.

A good example is somebody living in Miami,

-The temp is 85F with a dewpoint of 76F. The Pressure is a standard day of 29.92"hg or 1013.5Hpa. Guess what your turbo is operating at a density altitude of over 2,000 feet above sea level!

-Salt Lake City Utah, the temp is a typical summer day 95F dew point of 60 and the atmospheric pressure is a bit low at 29.65" Your turbo is operating at an altitude of over 8,250' or twice your actual elevation.

-Denver Colorado Warm day again at 95F but the humidity is up just slightly with a dew point of 75F. The pressure is a little low just like Salt Lake city of 29.65" your turbo in this case thinks its at 9409' above sea level.

Take a car that is modified, has a jammed VNT from babying it too much and factor in summer temps and you have a recipe for disaster or at the least a new turbo.

Winter months also take their toll, driving a TDI in the winter regardless of style already has lower exhaust gas temperatures. This causes more soot to form during warm up especially when you are driving the car lightly. The higher soot formation from longer ignition delay in the fuels stacks the deck against you in terms of jamming up the turbo. Somebody that lets their car idle in the winter really has no idea how bad this is for the TDI especially with the oil that is getting sucked into the intake from the turbo seal.

The best way to drive a TDI is firm throttle application, get up to speed as quickly as possible, keep rpms at or around 2,000 rpm in town or if you are on the highway in 5th gear and like to hold up traffic doing 55mph then fine the car can live through that because the load is sufficient to keep the heat up in the exhaust and burn off the carbon/soot.

Shifting at 1300 rpm in the city and letting the rpms drop to near idle is absolutely the dumbest thing you can do to these cars whether you have an A3/B4/A4/A5/B6 TDI.

DB
 

gdr703

Veteran Member
Joined
Jun 13, 2002
Location
Vancouver, Canada
TDI
Golf 2 door 2002 Indigo
Drivbiwire said:
Higher loads ie "Spirited" driving causes the EGR map to reduce the amount of EGR thus reducing the soot injected.

Again low engine output causes EGR to INCREASE not decrease.
I think we are saying the same thing, only I phrase it as, drive with a heavy right foot.

cheers.:)
 
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