Just Wondering:44mpg fwy @2K rpm or 3.5K rpm = OK?

My stock 96 Passat wagon with a 1Z engine and stock tires, rims and no mods seems to be stuck on getting 44 mpg on a 2500 mile road trip around the desert southwest I took last week.

The engine has 6K miles on it but everything else is around 140K miles including the turbocharger.

I did all the recommended stuff like clean the intercooler loop, air supply system, etc.

It has a new MAF and N75 soleniod & 900 relay and is using Redline Synthetic 10-50 oil in the engine and Redline lube oil in the trans.
Clutch is new.

No Vag-Com fault codes before or after the trip either.

Point is regardless of me going 80 mph across Arizona for hours or leasurly driving back home at 60 mph all the way the results are the same.

44 miles per gallon is the best the car does.

Tire pressure was varied as well and still no impact.

Going out was 28 pounds and back home I maximized it to the top allowable of 32 front and 34 lbs rear for my Bridgestone Portenzas.

I am wondering if stock Passat of this year get better mileage or not.

Around town has been about 35 to 37 mpg. on dino fuel and a bit more when I use 100% bio fuel.

Any ideas about improving my mileage on the highway?

I am not after performance - just economy.

I am considering increasing my gear ratio by getting larger diameter rims and tires.

Any other suggestions or comments on this little mystery?
I really think there must be something wrong when my mpg is the same when I push the car or baby it when driving cross country.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I would be very surprised of you got 44 MPG driving 80 MPH most of the tank. Driving 60 MPH, yes, but not 80.

60 MPH gets you 50 MPG for most folks, although your Passat is heavier and has an older design engine.

44 MPG sounds right for the average fuel consumption driving at 80 MPH for some of the trip and 60 MPH for the rest.

I could be all wet though.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

If the engine is new it will take some time to get peak cylinder pressure. Also 10w50 oil is pretty thick?

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

And you're complaining? 44mpg for a car that size is damn good. I would say that nothing is wrong with your car. It may seem odd that you're getting the same mileage no matter what but I really wouldn't be too worried about it...

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

44mpg is BAD?? My 2001 jetta has never gotten anything better than 42....I think something's wrong with it..

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Not many places on the interdweb where 44 MPG is an issue to be concerned with.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I would be very surprised of you got 44 MPG driving 80 MPH most of the tank. Driving 60 MPH, yes, but not 80.

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See...
I agree. It sounds wierd but I did the test pertty well.
I filled up to the top of the spout at Needles CA right on the border of Ariz on I-40.

Then drove east to Flagstaff going 80 on cruse control and then down to Phoenix on Hwy 17 and back to Flagstaff where I again filled up to the neck. I was climbing mountains and going 80+ all the way. My mileage was 44 mpg when I did the math.

After the marathon push I rested and drove back to the SF Bay area in a 15 hour leisurly cruse at 64 mph ~ 2200rpm.

Filled up at home and was totally surprised that the car got 44.3 mpg for that leg of the trip.

That is the mystery. Should of been a big difference unless there is something wrong and my system is tuned for better economy than 44 mpg yet cannot achieve it due to some worn part or faulty setting.

Local TDI Club owners tell me the 95 and 96 passats have the highest gear ratio standard transmissions ever made for a VW TDI so lower rpm at crusing speeds compaired to a newer Jetta or Passat is expected.

I guess I am spoiled by the initial reports of 60 mpg that I read on the TDI forums back before I got a TDI and became a member. I do an extraordinary bit of long distance driving for work at times and wanted a real exceptional fuel economic vehicle.

Maybe this is something for discussion next time I am at a TDI Club local get together.

Thanks

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Did you vent both times?

AFIAK (these are rough numbers though):
50 MPH = 70 MPG
60 MPH = 60 MPG
70 MPH = 50 MPG

So maybe 80 MPH does get you 44 MPG...but I'd guess more in the mid to high 30s. Average the 30-something MPG and 60 MPG of 60 MPH and you get close to your 44 MPG.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I think Bob's got the right answer here. I bet you didn't get a full tank on the fill up after the 80 MPH stuff. That way that MPG would seem high, and the return would seem lower if you did get a complete fill after the leisurely leg.

FWIW, I get 46 if I keep it under 75, 42 if I go 80-85. If I have a snowboard rack on the roof I get 40 at 80-85. On winter fuel, of course.

I drove three friends to NH yesterday at 80-90 MPH (what the traffic moves at around here) with a snowboard on the roof and got 40. Tell me what other car can do that?

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I wondered if someone might question my fuel fillup.

I was totally anal about being exact to the point of scribing a line in the fill neck just down from the vent valve by about 4 inches.

I take a good 10 minutes to fill my tank by hand throttling the nozzle to the lowest flow after it initially clicks off by itself. I have learned a trick to use the end of the nozzle to keep the vent valve button open and then I sit around for about 5 minutes while I slowly add another 3 to 5 gallons to the tank till non-foamy diesel reaches my scribe line.

So the mystery is still there but perhaps not so much.

44 mpg at 80 seems actually good results from what you all are telling me. 44mpg at 60 does not but may be due to the fact that my engine only has 6K miles on it so far and has not fully reached its efficent level at rpm around 2.5K.

Thanks for the general info about fuel vs speed. A good go-by that I will keep in mind.

Also maybe my mileage is a bit better than most because I was driving the desert southwest where things are not quite as cold and also where the diesel is a consistant high grade/ low-sulfur quality and does not have to be winterized.

Did I mention that I usually use 100% biofuel around town that has real high cetaine ratings. On the road I am limited to dino fuel but I wonder if some residuals boosted my mpg.

Thanks

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Any difference in winds? Did you get a tail wind going east and coming back west to Flagstaff and then fight a headwind all the way to SFO?

Otherwise I have no idea. I pretty much see a direct affect on speed vs. economy in my car.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I would think you were driving into a headwind on the way back. The other thing to consider is the humidity. TDIs run more efficiently in moist air. I didn't get great mileage in Wyoming/Montana/Colorado this summer and I was told the arid climate is a factor.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Wind direction and Humidity.

Had not factored in those concepts. Could they really make a 6 to 8 mpg difference. Probably.

I chased a storm going east so the wind was mostly to my back or side except for the return leg back from Phoenix which headded right into the wind.

Going back to SF Bay Area was aginst mild prevailing dry winds so maybe that is a factor in the low fuel efficiency on the going home leg.

I thought getting good fuel efficiency was just about fussing with the engine and fuel injection settings.

Locals tell me if I put in larger injectors and "chip" my computer in just the right way I can shoot for economy rather than performance and boost my mpg.

Apparently I should also squeeze out a mpg or two by removing the snow screen & getting a low-resistance air filter.

One could spend more money trying for the elusive high mpg than one could recoupe in savings in fuel over a 10 year time.

Bigger tires, rims, new injectors, chip ... that's hundreds of dollars.

The difference between me getting 44 mpg or 50 mpg on my trip was 7 gallons of fuel. Or about $15.00. It would take a whole lot of 2K+ mile trips to come out even.

I think I will stop my quest and be happy with what I have.

thanks for the round table review.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

One could spend more money trying for the elusive high mpg than one could recoupe in savings in fuel over a 10 year time.

Bigger tires, rims, new injectors, chip ... that's hundreds of dollars.

The difference between me getting 44 mpg or 50 mpg on my trip was 7 gallons of fuel. Or about $15.00. It would take a whole lot of 2K+ mile trips to come out even.

I think I will stop my quest and be happy with what I have.

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I love ya, man. Well, I don't loooove ya, just love ya.

The engine has 6K miles on it but everything else is around 140K miles including the turbocharger.

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New engines need to be broken-in, and will return lower mpgs until they are. Your road trip, with varying speeds and loads going up and down mountains, etc., was very good for your newish engine.

Redline Synthetic 10-50 oil in the engine and Redline lube oil in the trans.

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That is a heavier motor oil than most of us use. I don't know whether that is good or bad for a new engine. I imagine some might suggest a lighter-than-usual oil during the early. break-in period.

44 miles per gallon is the best the car does.

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It will get better. It always does.

Going out was 28 pounds and back home I maximized it to the top allowable of 32 front and 34 lbs rear for my Bridgestone Portenzas.

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Is that what is says on the sidewalls of your tires?

I am considering increasing my gear ratio by getting larger diameter rims and tires.

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That might work. You have 14" wheels/tires now, right?

After the marathon push I rested and drove back to the SF Bay area in a 15 hour leisurly cruse at 64 mph ~ 2200rpm.
Filled up at home and was totally surprised that the car got 44.3 mpg for that leg of the trip.

Click to expand...

When traveling in a westerly direction, you will nearly always have a headwind.

One other possibility: different fuel blends in Needles and Flagstaff? Fuel in Flagstaff would have to be fully-winterized, while the fuel in Needles might not be? And maybe when you filled up in Needles, you still had some of that high-BTU fuel in your tank from where you'd filled up previously?

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Unless seriously plugged up, removing the snow screen won't increase economy. A "low resistance" air filter is just asking for trouble... Do a search on K&N.

TornadoRed

Hi.
Thanks for the point-by-point reply.

Some answers to your questions.

Local TDI Clubbers use 10-50 Redline Oil so I did as well, did not consider needing a lighter weight due to a new engine. Going back and looking over data sheets of Redline, in its product literature, it states their 10-50 is a true multi weight that conforms to new car needs. I think I am safe considering it never freezes at home and I drive in 40 to 70 degree weather from Nov. to May. I buy my Redline in bulk 5 gallon containers at 4 containers/lot to get a discount so this is what I will be using all year round for the next few years.

[ The stuff is made in Antioch, CA, just a few miles from one of my work jobsites and I have learned I can get it from a marine diesel supply house along the Sacramento Delta at wholesale commercial rates by using a buddy who has a tug boat to get it for me. ]

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Yes, the max recommended tire pressure of my Bridgestones is 36 lbs but I called TireRack, where I got my tires, and leaned on their expert knowledge for the final 32 front & 34 rear pressure idea. They were the one's that suggested the max. pressure ratio for the weight of my car ( which they had in their database ) and the estimated additional load of passengers/contents. [ Their access to such info is truly amazing - they are a fine resource for tire knowledge.]

From everyone's input I have relaxed and will wait & see what my mpg does over time as the engine ages.

I may change out to larger 15" rims and get taller sidewall tires next time I need tires to lower my rolling rpm at 65mph. I am using the 4 lug pattern right now and have not seen VW 15" rims that use only the 4 lug pattern, they all seem to be the 5 lug. I am a mizer about spending more $ on this car so I will wait till I find cheap good rims that fit my current lug pattern before I consider a change out.

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Your idea of fuel grade differences is what I also speculated over. I am back home again and have filled up with biofuel.
I will note my around-town mpg in a week or two when I fill up again just to complete the data on this car's current efficiency and some of the suspect variables involved.

thanks

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Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

RE: Snow screen & air filter concepts...

GotDiesel?

Hello.

Some of the local TDI folks are real gung ho over pulling out all the air screens to squeek out a few more mpg & get better speed performance.

They take out the snow screen, and even the two screens on the air sensor/MAF.

It was the locals that suggested a oil-dampened, high velocity air filter element.

This S.F. Bay area is, after all, an urban mild climate area that never sees snow or much for piles of leaves or high dust levels.

That said. I am not in favor of drastic mods to my car's system. I may consider removing the snow screen just because mine was so corroded and falling apart anyway.

Right now I have a stock VW air filter in place and probably will continue with the same.

Thanks for the word of caution.


By the way... What is K & N?

I'm sure you already know that 5-40 full synthetic is the factory spedified oil, regardless of new or old engine. VW originally had a broader spectrum of approved oil weights with the 1Z engines, but had problems in the field with startup turbo starvation. Redline doesn't make a 10W-50. Are you using 15W-50 or 10W-40?

Changing to 15" wheels is usually the wrong direction to go for fuel efficiency unless you use super lightweight wheels to compensate for the mass of the wheel located further from its axis. Taller, narrower 14" tires on the stock (or lighter aftermarket wheels) should yield the greatest potential for fuel efficiency increase. BTW, 15" 4-bolt aftermarket wheels with the correct offset are definitely available, though not in as wide a selection as 5-bolt models.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

Interesting that Tire Rack recommended a higher rear pressure than front in a front-drive car. The pressure guide in my wagon asks for a 2 psi lower rear pressure unless the car's fully loaded. I typically run 32F/30R because I like the ride at those pressures (15" wheels). But the differential is important to reduce understeer and to keep the front wheels from rolling over onto their sidewalls in hard cornering.

Thanks for the oil & wheel info.

Redline produces a sub-market marine diesel oil sold by supply houses under their own label, with limited distribution and no product labeling other than a materials datasheet taped to the side of the can. It specifies that it is 10-50 all synthetic oil for use in 30 degree to 110 degree weather.

I drive the desert southwest a good bit in very hot weather and need the 50 weight when I am out in 100 degree plus days.

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Good heads up about tires/rims.

I was advised to consider keeping my sidwall rubber from being overly tall to assist in general handling and in case of blowout one has a chance at better control with a less tall tire sidewall.

No one till you, now, ever mentioned to me the issue of additional mass load. Good thing to consider.

Wonder if the bearings and spindle are up to the increase load?

Are stock, stamped steel rims that much heavier? Good to know there are 4 lug patterns out their in 15". Before I do any size upgrade I will investigate what the weight is of any rims I might get.

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

As far as tire pressure balance from front to rear.

I mentioned my discussion with TireRack included our estimate of passenger & content weight... What I did not mention in my previous thread was that there was over 500 lbs of engineering drawings and test equipment in the back of my wagon during my last trip. That is why the pressure differental front to back.

Nice bit of info about sidewall wear during cornering.
I am not an enthusiast so hard cornering is not much of a feature of my driving but it does happen sometimes in normal use so I will keep that idea in mind.

I usually drive with 28 lbs on the front and 24 in the rear when the car is empty of stuff to maximize contact with the road. My car has issues with skidding alot in wet weather during breaking and till it is resolved [ thinking of installing ABS ] I wish to maximize the footprint and favor increased rolling resistance.

Later...

Re: Just Wondering:44mpg fwy @2K rpm or 3.5K rpm =

I don't recall reading anybody claim to get better fuel economy without a snow screen. But I don't think there would be any harm in removing it either.

The screens around the MAF should definitely be left alone as messing with them screws up the calibration.

I don't know about the older style Passat intake but on the A4 series there is a spring-loaded flap that would open and allow adequate airflow if the snow screen were to become fully blocked.

Good luck.