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At long last my TDI has arrived in Oregon. Picked it up out on the edge of town, plugged in the ScanGauge and immediately drove back in to the Biodiesel station for a fill-up. Obviously it'll be some time before I get the SG calibrated so the numbers could be off by several percent either way, but it's been interesting watching the FE in a relative sense.

After the fill up I drove about 20 miles around town doing errands, purely city driving with lots of stoplights. 48mpg indicated. Great! Even if the SG is optimistic that's pretty good for a first timer. I'm already getting a feel for the sweet spot of acceleration for FE. Seems to be easier to find than on other cars.

What surprises me is that despite being a torquey diesel, this car is a lot less tolerant of lugging. An accidental shift into 4th at 15mph actually killed the engine, and I've learned even rolling starts in 2nd gear can easily kill it. Also, making the engine do any work at all below 1200rpm actually seems to hurt FE on this car (and is a major no-no because lugging causes this car's EGR to spew soot back into the intake). I'm pretty easy on the throttle, and so far under my foot it seems best to keep the revs between 1200 and 1800 when the engine is actually doing something, and upshift for lower rpms only if I truly am loafing along not doing anything. It's funny, although I tried to avoid major lugging on the Subaru, I certainly did err in that direction and run the lowest RPMs I could get away with because it didn't seem to hurt FE. I could even stomp the Subie to the floor going up a hill in 5th and the consumption would only increase about 0.1gph.

The other side of the coin is that the TDI seems to respond very well to pulsing and coasting. Probably a combination of the very efficient idle (SG indicates 0.1gph) and the very efficient power delivery between 1200-1800rpm. I credit that for the 48mpg (indicated and not actual, admittedly) newbie result in city driving. The pulses seem to drop the trip average a lot slower than I'm used to.

What's odd is that I'm doing better in the city than on the highway. What, did I accidentally buy a hybrid? ;) I only saw about 42mpg indicated on the 14 mile, ~60mph drive into town preceding all this city driving. Another ~10 mile freeway drive yielded similar results.

Could it be the tires? I know the tires on this vehicle (Bridgestone Potenza G009) are only rated "fair" for rolling resistance by Consumer Reports, as opposed to my usual Toyos which are rated "excellent". The highway FE seems at least 10% lower than I'd expect. Can high RR tires make that much of a difference on the highway? I'll check the wheel bearings after the next freeway drive too, just in case that's the hidden culprit.

Wow congrats on your new ride. I have certainly looked at these cars in the past. If you haven't already, you should take a look at tdiclub as they have plenty of information available about mods you can do and general diesel maintanance for the TDIs. Supposedly some of the aftermarket chips can increase your fe.

Congratulations on the purchase, these cars can be great fun and have lots of FE potential. A thing I've noticed about the engine is that it doesn't care much for drivers stepping on the accelerator while letting out the clutch. Trying to do a 2nd gear start with plenty of throttle like with a gas engine doesn't work very well. As soon as the engine gets loaded, the rpms drop very quickly.

An interesting thing though is that the ECU tries to keep the engine from stalling if it can. You can do 2nd gear rolling starts without touching the accelerator, just keep the rpms above ~800. As you release the clutch, more fuel is injected and the engine makes more power to try to bring itself back up to idle. You can also coast along at idle in any gear without touching the accelerator.

42mpg at 60mph does sound low. I have an Excel document on my other computer which I will try to post for you tomorrow evening. It estimates fuel economy for a TDI at given speeds. Plenty of variables, such as rolling resistance, weight, and aerodynamics can be adjusted. I think steady cruising on average tires at 60mph was around 55mpg in that document.

...
What surprises me is that despite being a torquey diesel, this car is a lot less tolerant of lugging. An accidental shift into 4th at 15mph actually killed the engine, and I've learned even rolling starts in 2nd gear can easily kill it. Also, making the engine do any work at all below 1200rpm actually seems to hurt FE on this car (and is a major no-no because lugging causes this car's EGR to spew soot back into the intake).



That is strange. I have driven toyotas new 1.4 l TDI engine, and it clearly uses some regulation to control idle. It tolerates load at idle just like my toyota petrol engine.

congrats on the purchase..

I'd imagine once the engine is broken in your FE will rise

Have fun with it, as I've said before, my gf has one and she drives like a maniac and still turns out great fe. Check out TDIclub.com. Also, don't forget to drain the water out of the fuel filter regularly or the plastic screw on the bottom will break when it freezes.

Hi WriConsult:

___Congrats and finally :Banane52::D :woot:

___I was very fortunate to drive Sefton’s after it was warmed up and SG-II equipped and oh my god did it allow some great numbers in below freezing temps and snow covered roads during what most would call a blizzard!

___Good Luck

___Wayne

Very nice. Got any pictures of it?

seftonm, I'm already noticing what you said about the RPMs dropping quickly. Even in 1st gear I have to give it more juice when starting out than on other cars.

And also noticed what you said about the ECU sending it more fuel if it senses an rpm drop. If I'm light with the clutch I can get it all the way up to 25mph (in 4th gear) without ever touching the accelerator. Possibly even faster: this was in traffic so I haven't fully played this experiment out yet. It definitely uses fuel to do it though -- at one point the SGII indicated 0.6gph while I was doing ita -- so I'm not sure if there's any benefit to doing things this way.

I haven't taken any photos yet, but here are some that the seller took. The car is a 4dr in Flash Red: the most intense, retina-burning red I've ever seen on a car. In any kind of daylight it has a magenta hint to it, as you can see in the door handle photo. Huge cop magnet. Good thing I don't speed! :D

http://a964.ac-images.myspacecdn.com/images01/120/l_0fd380467a110c7292ce3013a92fda13.jpg
http://a600.ac-images.myspacecdn.com/images01/127/l_d0e5a488975a7afb6ece170e290f8b1f.jpg
http://a655.ac-images.myspacecdn.com/images01/65/l_9e515c39df89c512f866b29dd301e84e.jpg

... the most intense, retina-burning red I've ever seen on a car...
That's the truth! :cool: Looks great!

Sweet, WriConsult!! We are going to see some awesome numbers from you very shortly I'm sure. :D

Thanks for sharing the pics -- that's a great looking car. :)

Hi WriConsult, you are probably right about there not being much FE benefit to just idling along. I don't do it very often but do find it nice not having to work the accelerator while when stuck in crawling traffic.

I found the Excel file I was talking about:
24033Fuel_economy_TDI_model.zip (http://www.cleanmpg.com/forums/downloads.php?do=file&id=26&act=down)
It estimates 57mpg at 60mph. How many miles are on your car? It may still need breaking in.

Most turbo diesel engines have a sweet spot for BSFC that is somewhere in the middle of the RPM range between maximum TQ and maximum HP. The most efficient fuel usage per HP output is usually during full load.

I know it sounds wrong, but just check out tractor tests at the Nebraska tractor test lab and Cummins' own web site. Fuel usage per HP goes up when at light load. So it might be as well to accelerate briskly in the appropriate RPM range.

Also loading the engine below turbo boost RPM uses fuel less efficently.

Not bad - not bad at all!! :)

Hi Rweathford:

___You are just going to have to trust the numbers achieved from the diesels, hybrids and non-hybrids we have driven in the past and throw the BSFC maps out of the window. They do not point the way to the best FE by any stretch.

___Good Luck

___Wayne

Swapped out the tires for my favorite LRR choice (Toyo Tourevo) yesterday, and still seeing way higher city mpg than hwy mpg. A couple trips done after the tire swap:

A 30 mile loop last night at 50-60mph yielded only 44mpg indicated. Rainy conditions admittedly, but that only costs me 1-2mpg on the Subaru with the same tires. I'm at least 10mpg below where I think I should be here. That 30 mile trip included a 2 mile segment from my home to the entrance ramp at 74mpg indicated -- with a semi-cold engine.

A 15 mile trip at 40ish mph on (also rainy) parkways yielded 67mpg indicated.

Tank average has been holding at 46-47mpg indicated (which also included a fair amount of driving in snow yesterday), but ironically it's city driving that is keeping the numbers up. I'm consistently getting near 50mpg in uncongested city driving using my usual hypermiling techniques.

To get the same mpg at, say, 50mph, I'd need to be consuming 1.0gph. But steady state 50mph seems to require 1.1-1.2gph, so I'm not even getting 50 at 50. Considering this thing is rated 49mpg hwy, something's wrong here.

Unless of course the SG is calibrated way low, but if that is the case then my city mpg is really off the charts!

Now that I've eliminated tires as a variable, what else could do this? Plugged air filter? The only other thing I can think of is an aerodynamic problem, but the vehicle sure looks normal on the outside. I'd think anything aerodynamic that's sapping 10+mpg would be pretty obvious.

Hi WriConsult:

___Lift each wheel and give them a spin. That would eliminate that variable. Then you have the alignment … At idle, you should see .3L/hour vs. .3 gph you are probably used to seeing. She should also be able to idle if you bring her up off the clutch slowly in all 5 gears. She will be trotting along at 20 mph hour or so in fifth while at a touch above idle and be perfectly fine in doing so. At least that happened in Mike’s TDI two months ago?

___I do not believe I ever got over 50 in Mikes so hopefully he will give you a much better idea as to the highway consumption. These things are not all magic but getting 50 at 50 does sound a little low other than you are in the middle of winter with the RRc doubled, road conditions poor at best and who knows what kind of winds. Winds only help for about 25% of the compass and hurt the other 75%. Are you are running set at DieselA vs. B? This is not a Fuel setting but a Calibration. It took us a while to figure that one out in Mike’s as the numbers are fubar until that swap was complete.

___Good Luck

___Wayne

Hate to mention it, but how's the clutch? Slippage usually shows up in high gear first. It wouldn't take much to lose 5-10% efficiency.

beautiful car !

Wayne:

Yes, it shows 0.1gph at idle. If I'm ginger with the clutch I can get it up to 35mph without touching the accelerator, although I'm not sure I've tried it in 5th. I will do that.

I don't think winds are a factor because they've been pretty calm this weekend, I'm getting this consistently even in out-and-back and loop trips where wind should cancel out. I realize cool temps hurt, but that's 35-45 F here. Not exactly the kind of cold you guys deal with in the midwest.

I am running at DIESELa.

I'll try lifting the wheels and making sure they spin freely. Also when I take it out for some more controlled testing this week I'll do several runs at various speeds in both 4th and 5th gear. Trying to figure out the pattern at exactly what speed and/or rpm the mileage drops off.

A big issue with diesels is fuel quality. Try running non bio from an outlet that sells a lot of fuel just to see what happens. Also, if the fuel filter is garbaged up there will be efficiency losses. It may not make sense, and I have no explanation other than personal experience.

Keith

Yes,

Bio will lower your numbers. I see a 0.5 - 1 MPG drop on a 6-7 MPG average. (Semi)


Dodge/Cummins pickups will actually do better MPG in the city driving than constant highway. Anything above 45-50 MPH and it starts dropping. However you can maintain over 20 MPG around 60 MPH if you are nice to it.

Hi Rweatehrford:

___Are the Cummins equipped HD Ram’s geared a bit short given the quick fall off? IIRC, the F-250’s with the 6.0L PowerStrokes were running ~ 1,800 at 55 (that memory is fading fast unfortunately so do not quote me on that :() and I thought that was a bit high for FE although I understand it completely if towing? These trucks could be shaped like a piece of plywood perpendicular to the wind (they are cone to think about it ;)) and the PowerStroke’s, Cummin’s and Duramax’s would still probably only need to output just 40 – 50 HP at 60 which they could do practically at idle?

___Good Luck

___Wayne

Since I'm burning B50, I know I'm getting a 4% loss vs. petrodiesel, but that wouldn't explain why hwy mpg is so much lower than city.

By the way, I also found the hwy mpg to be poor when I initially picked up the car and the tank had pure petrodiesel in it, so I don't think biodiesel is the issue here.

I will check on the fuel filter too. Thanks for the tip, Keith.

Checking filters and how the wheels spin are good first steps that solve most problems. How does acceleration / power feel in the car? If you can, try driving about 2000 rpm in 5th, mash the accelerator to the floor, and hold it there. The car should build speed smoothly without any stuttering. This is also a good test for a slipping clutch. If you feel stuttering in any gear, try unplugging the MAF and repeat to see if it gets better. What kind of oil does the car have in it?

I was out driving yesterday and the SG was showing a touch over 60mpg at 50mph in 5th. If you're not using cruise control, try running with cruise on to see what the fuel economy looks like. You may be trying to do something that the car doesn't get along with when you're driving on the highway.

Hi Rweatehrford:

___Are the Cummins equipped HD Ram’s geared a bit short given the quick fall off? IIRC, the F-250’s with the 6.0L PowerStrokes were running ~ 1,800 at 55 (that memory is fading fast unfortunately so do not quote me on that :() and I thought that was a bit high for FE although I understand it completely if towing? These trucks could be shaped like a piece of plywood perpendicular to the wind (they are cone to think about it ;)) and the PowerStroke’s, Cummin’s and Duramax’s would still probably only need to output just 40 – 50 HP at 60 which they could do practically at idle?

___Good Luck

___Wayne


Yes, this is near the converter lockup MPH in OD. The aero starts to add up too. It is a big tall truck you know. :rolleyes: The problem lies in the few gears (4 with an automatic) and requirements to start a heavy load. Most people tow in OD instead of D because of the huge TQ values. The engines can handle it. Full power at 60 MPH in D makes about 7 MPG and OD makes about 10. This is full load, not just cruise.

With the 5-speeds (sorry I haven't driven a 6-speed) manual 1st gear is worthless unless fully loaded. You can actually start out the truck in 3rd gear if you slip the clutch. So in this case if using the truck as a car you could really use a taller rear end gear. The 6-speeds use basically the same OD gear ratio, just another gear somewhere in the middle.

The automatics use about a 30% OD and the manuals are 25-28%. Somewhere in that range.

I wish the trucks had more speeds (low speed start with load) and geared drive as a towing gear for 60-70 MPH (since most people drive them at those speeds and the driveline is more efficient) and OD for a cruising gear at 70-80 MPH. I know this goes against the FE Hypermiling, but hardly anyone drives 50-60 MPH but the people here. I'd like to see the lower end of the RPM range near the 1400-1500 so that the turbo can spool if necessary to keep from downshifting. Full TQ is also available near these RPM speeds. All accessory and friction losses are lower than where they are currently geared.


Many large Class 8 trucks run in the 14-1500 RPM range and it seems that Cummins small motors mimic the larger engines, just on a smaller scale. The newer common rail B-series motor is available to run higher RPM, but it's just for the HP war.

I run a Class 8 truck with a direct top gear which is more efficient, but also would like to have an OD on top of that when dead heading (empty). However with used trucks you sometimes get what you get.

Didn't some of the TDI's have issues with variable exhaust turbine vanes sticking and EGR valve plug-ups when driven too "nicely". Perhaps this is some of the problem?

A search on a good TDI resource could really help you out.

Didn't some of the TDI's have issues with variable exhaust turbine vanes sticking and EGR valve plug-ups when driven too "nicely". Perhaps this is some of the problem?

That could be part of it. If the vanes are stuck or the intake is clogged, my floor-it-at-2000 rpm suggestion could trigger a limp mode. If that happens, turn the car off and turn it back on again and power will be restored.

WriConsult, I just remembered that 5th gears are interchangeable between many different VW transmissions. It's remotely possible that somebody swapped the original 5th out for a shorter one. What is the engine speed 50mph in 5th? It should be in the 1700-1800 rpm range.

You may want to ask on tdiclub about your mileage, there are people there that know far more than any of us.

If you want to get a feel for where you COULD be fe wise, check out tdiclub.com. I think I saw some people on there getting 70+ mpg (not sure, but could've been a Polo).

...
I think I saw some people on there getting 70+ mpg (not sure, but could've been a Polo).


Imperial 70MPG or US 70MPG?

I managed 70MPG Imp (=56MPG US) in my passat on the 27m drive to work this morning and yesterday, and the passat is much larger / heavier than the golf. Last tank was 61.7MPG imp (=49.3MPG US).

That must have been what it was... But I bet someone could wring one to just about 60 US for a tank.

All I know is I can get from CT to VA (total trip time: 8hrs) on a tank and have enough left over to get to a gas station on the way back!

Well, I've been asking over at tdiclub (http://forums.tdiclub.com/showthread.php?t=203066) and not getting much help. I don't think a ton of people over there have extensive experience with ScanGauges, at least not with monitoring them as closely as we do here at cleanmpg to improve our driving technique.

No one who has replied to the thread seems to think it's a problem that the ScanGauge is indicating much higher fuel economy in serious urban driving than at a steady 50mph on the highway. The replies so far are either:

Well, you haven't calibrated your SG yet, so how do you know there's a problem? Burn through a couple tanks, calibrate it and then come back.
The SG is not consistently accurate (maybe particularly on TDIs?) under varying load conditions.


I hope it's the latter, although i'm disappointed because I've gotten used to the SG being pretty accurate (after calibration) on the Subie.

If it does turn out to be accurate and we don't figure out the cause, I'm definitely doing a 5th gear swap. If the SG is accurate, then my steady state tests yesterday (see the above thread for details) definitely show RPMs to be the biggest factor.

Hi Maxx:

___Once you get a feel for the place, you will discover at least 200 members that could squeeze at a minimum 60 out of a tank from a 1.9L TDI. Just seeing the SG-II attached to Mike’s for 10 minutes told me it is just an older version of the iCDTi we had the opportunity to drive last summer :) Darn things have a lot going for them to say the least.

___WrConsult, what are your R’s at 55 mph? As for the SG-II cal, at least you are in the ball park when first installed but let us see what a tank turns out to be before you get too excited. The TDI’s can be worked to do magical things but they are not the magic all by themselves ;)

___Good Luck

___Wayne

Check a few of these things in this order (easiest to hard):

1. Turn your ignition to II position (radio/vent air come on). If you hear a click, the solenoid on your turbo that opens the veins is fine. Start driving, if you do not hear a whirling whizzz sound between 1500-1900 rpms (and the car lags instead of takes off like a v6) you probably have a turbo related problem and that really blows.

Search tdiclub for "turbo doesnt work" or something like that, they have tons of write ups. I recently had my turbo shut off on a very cold day doing an acceleration past a truck. You will only be able to engage the turbo by turning off the car so it resets.

2. Remove airfilter housing. Off to the right (on a jetta a4 tdi engine at least) you will see the intake snorkel for the airhousing screwed onto the body frame. Take that off and check your air snokel screen for dirt/bugs. Its a bad design and my 03 was 90% clogged with sand when i bought it in 06. Did wonders after i cleaned it.

3. (looking at the car) under the left headlight is the intercooler. If the body is blocking the fins, or anything else, remove it. I also took off the hose from the EGR (at the point it hits the intercooler) and dapped about 1/2 a roll of paper towels filled with an oily substance. It was a result of bad build up at the EGR because of improper vehicle operation and higher sulphur diesel before 10/2007. I had the EGR cleaned as well, worked wonders for acceleration (local Tdi guru did it).

Truthfully number 2 worked wonders for FE increase. Also driving a tdi requires slightly different technique than a gasser. Not pushing the RPM high enough is what caused EGRs in the past to clog faster. Recommended shift is at 2600-3000 rpm...i do it at 2600 approx. If you are under hard acceleration try not to shift so your next gear is under 1900 rpms....and sunday driving in the 1500-1900 rpm range instead of crusing over 2000rpm is a good way to blow your turbo out (overheat with not full fan speed if i recall). You have bought a fine car, hopefully it gets better!

(ps. on deceleration in a gas manual, you would normally coast in N or turn the car off to hypermile. Engine braking in a tdi is sweet, the intake air will push the pistons withoud fuel and obviously there is not spark...so not only dont you use fuel, you dont use brake pads in a lot of slowing down situations)



EDIT: Also with step 1...with the engine on, open your hood and check for vaccum lines that may have come disconnected. I had this happen once after maintenance. Another problem could be a leak in a vaccum line, some as small as pinhole size. Those are hard to find, tdiclub has a good writeup on what to order to replace them 1 by 1 if needed.

Hi Toast:

___Welcome to CleanMPG and great first post too!

___Engine braking in a modern day SI-ICE is a no fuel use solution as well but boy does that big compressor take a drain off your fuel free distance once invoked :(

___Good Luck

___Wayne

Hi Toast:

___Welcome to CleanMPG and great first post too!

___Engine braking in a modern day SI-ICE is a no fuel use solution as well but boy does that big compressor take a drain off your fuel free distance once invoked :(

___Good Luck

___Wayne

thanks.

ha! its an art to drive a tdi unfortunately...on top of hypermiling. engine braking i use in situation like off ramps when i know im probably going to stop, or if a hill is super steep going down and theres a stop or turn. I use N when im coasting down a grade that would ultimately slow me down to fast to benefit under engine braking.

Im trying some moderate hypermiling experiments, nothing like you guys though. I get 49.7mpg under normal driving without any thought of hypermiling, and 44.xmpg winter because of extreme warm up times and winter fuel blends. i hope to increase 10% for each.