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Z3 2.5 Gas mileage

12K views 36 replies 14 participants last post by  gmushial 
#1 ·
Anyone know what kind of fuel economy I should get with a Z3 2.5 liter? I have an automatic.
 
#2 ·
If you want to know your fuel economy, your car can tell you that. I have the on-board computer that can display the Miles-per-gallon. I'm not sure if your model has that. You press the turn-signal arm inward to change between the clock display and other functions.

If that doesn't work, you can try this:
http://www.bimmerfest.com/forums/showthread.php?t=202377

However, I have to say that I never considered fuel economy. That's not why I bought the car. If that's your main concern, BMW offered a 1.9 engine with a manual transmission that may fit your needs.
 
#4 ·
20-21 MPG? It sounds like you're not driving right. You should be getting 16-18 with this car.

Actually 20 for city and 25 for highway is typical, so you're about right. Keep in mind that the car takes high-octane fuel; lower octane will result in lower power and lower mileage. Also, ethanol has less energy per gallon and will result in lower mileage.
 
#6 ·
Many have reported better mileage with higher-octane fuel. You'll have to make the trade-off for yourself. Go to the top of the page on the right, click on the box labeled "search this forum." Enter something like "octane" and you will get lots of opinions, reviews, test results. etc.
 
#8 · (Edited)
Mpg.....

My '99 Z3M with 93 octane non-ethanol gets between 25-26 mpg. I don't drive it for better mileage... but I don't drive like an idiot either... (most of the time). I drive 15 miles to work. What I would call semi-rural highway. 2 red lights, 3 stop signs.

Crappy : )

(Just outside of Nashville)
 
#9 ·
I have the exact same car. I get 25-26 mpg on 91 oct premium and 23-24 mpg on 89 regular.

If you do the math it turns out it's cheaper to run premium usually.

Why the difference? As I understand it the computer "de-tunes" the car when using reg by retarding the spark advance and get rid if pinging on lower oct gas. This also reduces performance and gas mpg.

I did this experiment several times and reg was always lower the premium on my car, same commute, same gas station.

So I guess it pays to put in premium.

-H
 
#11 ·
On my 2002 Z3 Roadster with 2.5 liter engine, I get about 21-22 mpg around town & about 28 mpg on the highway. I have even gotten 32 mpg while cruising at 55-60 on the highway recently. I did this several times (filling to the brim & refilling) to verify I actually could get that impressive mpg.

No sense to go overboard, however, about mpg. That isn't why you bought the car in the first place. There are many other cars that can do much better including hybrids.

Fred
 
#12 ·
My goal isn't to maximize gas mileage at all. I was just a little surprised at how low it is....so I was concerned that it was an indication that I had a problem. I bought it used and I have spent some money replacing vacuum lines and radiator, so I don't really want to take it in again.
 
#13 ·
JKrell, I have a 99 with a 2.8 and manual. The people that I bought it from swore that it got up to 32 on the hwy using 92 fuel. The best I got is 30mpg @ 75mph. That being said, I still get at least mid 20's around town and back and forth to work as my DD. I tried lower octane and it didn't work. From info in here, someone mentioned how low of a shift range they ran theirs so I tried it. That made the best bang for the buck in MPG. If I'm not in any hurry, etc, I won't shift over 2500 and I get all I can in gas mileage. If I'm shifting 3K plus, then I'm immediately dropping off about 3(ish) MPG or more. I would guess if you rev up and let the auto trans shift hard it would be like rev'ing the shift points on a manual. Just my couple pennies worth.
 
#14 · (Edited)
An OBDII engine continuously monitors and optimize its performance, so there isn't a lot that can go wrong without setting a code. Some subtle things might be a bad (or wrong) thermostat keeping the car in the warm-up mode or a bad temperature sensor making it think it's cold, but these are fairly rare problems. Cleaning the MAF sensor sometimes helps, particularly if an aftermarket oiled-cotton filter is used, such as K&N.

There could be other factors such as sticking caliper or parking brake, low tire pressure, or even softer tire design.

It could be the fuel you're using. Maybe the octane is lower than advertised, maybe it's high in ethanol, maybe it's oxygenated as required in some states.

It might also be the numerator part of the equation: maybe your odometer is off. Or rather everyone else's speedometer is fast. Most BMW owners report indicated speeds 2-3% higher than actual speeds. That would mean their odometers could be showing 2-3% farther than actually traveled. In any case, you can check your own speed and distance with a GPS system.
 
#15 ·
I use Chevron usually....I live in Arizona which requires oxygenated fuel, but only in the winter. I will try premium, but only to experiment. I don't think there is a problem. If it is low, it isn't by a whole lot, and probably due to factors I really can't control. I do think the car could be a little quicker on the low end....but it could be my imagination.
 
#16 ·
My automatic is a 4 speed, and I run about 2800 rpm at 70 mph.....my Acura is a 5 speed auto, and runs at a much lower rom at that speed. I imagine with a 5 speed manual, I would be getting much better mileage. I have an auto, and it is what it is. I sometimes wish I had a manual transmission, but I got such a good deal on the car, that I got what I got.
 
#17 ·
"I do think the car could be a little quicker on the low end....but it could be my imagination."

That could be a clue. That's one of the symptoms of a bad VANOS seal, along with reduced fuel economy.

Look over this website: http://www.beisansystems.com/

I was amazed at how much low-end torque I got after I replaced my VANOS seals. Since I bought the car used, I didn't realize how it was supposed to feel. Now the car is really strong from a take-off.

The Beisan seals are made of Viton or something similar and won't break down like the OEM seals.
 
#22 ·
...

I was amazed at how much low-end torque I got after I replaced my VANOS seals. Since I bought the car used, I didn't realize how it was supposed to feel. Now the car is really strong from a take-off.

The Beisan seals are made of Viton or something similar and won't break down like the OEM seals.
Just had my VANOS seals replaced last week. I'm also surprised by the increase in low-end torque and increased smoothness.

At 122K miles I actually thought my car was in pretty good shape. But, on cold starts, the car didn't seem quite as smooth or take off as easily as I remember.

The improvement is very noticeable.
 
#19 ·
The Beisan website has the most complete instructions ever. Look over those as well as the FAQ page and you should have a feel for how complex it is.

For a Single-VANOS engine, it takes some special tools to lock the camshafts. Other than that, it's only slightly more complex than changing a valve cover gasket (which you should do as part of a VANOS job).
 
#24 ·
FYI, I found that when driving the car below 3K rpm my MPG increased vastly. around town went from 22-24 MPG to around 25-26, the Fun factor took a nose dive however. I don't look at MPG anymore as long as it's within the range advertised on the window sticker, you're fine. Have you taken a long highway trip recently? Are you using the on board computer to get your MPG or doing the math yourself?
 
#25 ·
if the automatic trans is geared tall enough to only spin the engine 2800 rpm at 70 mph, you should be getting great mileage. the manuals seem to be geared at bit lower.

my 2.8 manual turns 3500 at 75 mph and the computer says 27 mpg.

usually, i shift before 3k unless i'm playing ronnie roadracer. the great thing about this engine is tractability and durability [i guess those are two things]. it's built strong enough to take high rpm but has so much torque it usually isn't necessary. a great engine and great looks; the rest of the car is kinda marginal. what a clunky gearbox huh?
 
#26 ·
Fwiw - for engines that are designed to take advantage of higher octane, the gas mileage increase with higher octane seems to offset the price pf premium fuel. Top teir gas matters. When we had to replace a cat on our 100000 mile minivan (*sigh* to having a minivan), the first quesiton the dealer asked was what type of fuel are you using. Over time, I have seen my CPO 2008 Z4 increase from 29 mpg to 32 highway after better gas had a chance to clean things out. I have become a firm believer in using name brand gas without ethanol if possible to improve the life of the engine and exhaust systems. It may or may not cost a few more dollars per tank. It will avoid an early $800 - $1200 cat repair bill.
 
#27 ·
Fwiw - for engines that are designed to take advantage of higher octane, the gas mileage increase with higher octane seems to offset the price pf premium fuel. Top teir gas matters. When we had to replace a cat on our 100000 mile minivan (*sigh* to having a minivan), the first quesiton the dealer asked was what type of fuel are you using. Over time, I have seen my CPO 2008 Z4 increase from 29 mpg to 32 highway after better gas had a chance to clean things out. I have become a firm believer in using name brand gas without ethanol if possible to improve the life of the engine and exhaust systems. It may or may not cost a few more dollars per tank. It will avoid an early $800 - $1200 cat repair bill.
 
#28 ·
I have a 2001 Z3 2.5 automatic which I bought a couple of months ago. I was driving easy and the computer was showing an average of 16 mpg. I checked the actual mileage against the fuel I was putting in the tank and found I was getting about 20 around town and 26 on the highway. So I recalibrated the fuel computer to the real world. Another thing I have checked is the speedometer - it is about 6% fast - does this mean the odometer is also showing 6% more miles? Is there a way to calibrate the speedometer I wonder. To calibrate your fuel consumption check this thread: http://www.bimmerfest.com/forums/showthread.php?t=178963&highlight=z3+fuel+computer
 
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