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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 10-30-2013, 08:10 PM
bmw530ii bmw530ii is online now
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Mein Auto: 2002 bmw 530i sport
Bad gas mileage

Hey everybody, I've noticed that my car is getting worse and worse every time I add gas. For example a when I first got my car a few months ago I would get around 17-21 miles per gallon mainly streets and now I'm barely getting 16 on the streets again. How is that possible? My daily commute is to drive to school and back which is about 10 miles round trip on the streets. I really don't drive my at that much because I don't want to add more miles than it already has (152k). Any solutions? Should I take my car to my mechanic? Thanks


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  #2  
Old 10-31-2013, 01:30 AM
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mjalloul11 mjalloul11 is offline
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Cold weather and short trips are sure way to bad MPG . Any SES lights? OR you could change the O2 sensors if they are over 100K old.
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  #3  
Old 10-31-2013, 03:01 AM
Burning2nd Burning2nd is offline
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If start with plugs
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  #4  
Old 10-31-2013, 04:42 AM
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bluebee bluebee is offline
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See also:
- What's the true accuracy of the various methods of mpg calculation (1) (2) & what gasoline mileage should an E39 really get (1) (2) (3) (4) (5) (6) (7) & what are some great e39 fuel efficiency stories (1) (2) (3) & what are the awful e39 fuel mileage complaints and miles per gallon diagnostic tests (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32)
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Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need
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  #5  
Old 10-31-2013, 08:03 AM
poolman poolman is offline
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Vacuum leaks abound on these engines and are hard to find,,but doable, The cooling system has it ever been upgraded? If so , do you know if the correct OEM thermostat was installed when it was worked on. If not ,,that can cause bad mileage when the temps start going down.
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  #6  
Old 10-31-2013, 08:20 AM
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Fudman Fudman is offline
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Reduced gas mileage is the first symptom of the change from summer to winter gas formulations.
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  #7  
Old 10-31-2013, 10:33 AM
bmw530ii bmw530ii is online now
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Mein Auto: 2002 bmw 530i sport
Bad gas mileage

I forgot to mention that I got my spark plugs replaced by a mech a few weeks ago. I'm not sure if the cooling system has been replaced, but I'm guessing that it has because I'm not having any problems at 152k miles. I'm not sure if the o2 sensors have been replaced, I'll ask my mechanic about it. I also am not getting and ses or ces lights


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Last edited by bmw530ii; 10-31-2013 at 10:35 AM.
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  #8  
Old 10-31-2013, 10:56 AM
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G-Moussa G-Moussa is offline
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I feel like i just started a thread about this a few months ago. Like everyone is saying, short trips and due to the weather change will decrease your mpg. Furthermore, in the winter as previously mentioned additives are added to the gas which will affect mileage. Keep an eye on it for now, my 540i is doing the same thing lately...
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  #9  
Old 10-31-2013, 05:04 PM
bmw530ii bmw530ii is online now
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Bad gas mileage

Thanks for the info. What gas mileage did you used to get and why do you get now? Thanks


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  #10  
Old 11-01-2013, 04:08 AM
bolderdesh bolderdesh is offline
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Mein Auto: 2001 525i
Bad gas mileage

It's quite simple: increase your MPG by... 1. Upgrading your fuel injectors. If they're the originals, they only have one hole for the gas. Upgrade to some 4-hole Bosch ones. You'll see better hp, mpg, and smoother ride
2. Lucas fuel treatment system. Yes this really works. Dump some of this in your tank at every fill up and you'll gain one mpg for sure
3. Tire pressure. If you really want to stretch your gas $$$, check your tire pressure very often. A nicely pumped set of rubbers can mean the difference between sweet success, and flat out failure
4. Weight. You got any school projects in the trunk? Take 'em out! You don't need the weight. Your car will perform better all together with less of that
5. Computer chip. A last resort, but a very effective one at that. The right computer chip will be one of your best bets against the the pump. Don't buy a cheap one though. Anything less than a few hundred bucks is not worth it
6. Cruse control. It's there, use it as often as possible

Hope this helps!!


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  #11  
Old 11-01-2013, 05:34 AM
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mjalloul11 mjalloul11 is offline
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Wow, with the price for fuel injectors and a chip i can tune the engine to factory spec and get like new MPG numbers.
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  #12  
Old 11-01-2013, 11:28 AM
bolderdesh bolderdesh is offline
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Bad gas mileage

Yes and no. You can get rebuilt fuel injectors from eBay for <$160. They'll do an amazingly good job for the price. That's actually what I'm planning on doing because my injector #1 error code is popping up.


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  #13  
Old 11-01-2013, 07:07 PM
bmw530ii bmw530ii is online now
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Bad gas mileage

I've been driving my car in the same manner as i did when I got it. I thought something was wrong with it, I guess not because from what someone said before it's the additives from the winter fuel. Their really is nothing in my car except my back pack in the trunk. I also don't want to spend money on injectors or ecu chips. Tires are low on tread I'm not sure if that helps mpg. Thanks for the help anyways


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  #14  
Old 11-02-2013, 05:08 AM
poolman poolman is offline
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Just where does one get the Bosch injestors to fit our 525 engines. I didn't think they were available ? I've looked around for those and couldn't find them anywhere but a special order from Bosch.
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  #15  
Old 11-02-2013, 08:09 AM
bolderdesh bolderdesh is offline
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Bad gas mileage

Quote:
Originally Posted by poolman View Post
Just where does one get the Bosch injestors to fit our 525 engines. I didn't think they were available ? I've looked around for those and couldn't find them anywhere but a special order from Bosch.
If you don't care about a retail price tag, phone up your local O'Riley. Here, you definitely pay for quality ($120.00 A piece). By route is eBay; all six injectors for 150 bucks


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  #16  
Old 12-16-2013, 12:51 AM
bmw530ii bmw530ii is online now
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Bad gas mileage

Is it possible that theirs a leak or something? I'm getting worse gas mileage as time goes by. Should I see a mechanic about this?


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  #17  
Old 12-16-2013, 07:48 AM
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eparayno eparayno is offline
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You have a 10min commute, why is this even an issue?
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  #18  
Old 12-16-2013, 08:05 AM
pshovest pshovest is online now
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If your CEL is NOT lit, there is likely no issue other then your driving style and short trips.
Get on interstate, set cruise control for 60 MPH, reset OBC MPG, drive for 10 miles, record the MPG.
Repeat on the return trip using same end and start points, record the MPG.
Report both numbers
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  #19  
Old 12-16-2013, 08:25 AM
ProRail ProRail is offline
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Quote:
Originally Posted by mjalloul11 View Post
Cold weather and short trips are sure way to bad MPG . Any SES lights? OR you could change the O2 sensors if they are over 100K old.
This is especially true if most of your trips are from a cold start. Cold starts really eat up gas, and in cooler weather it takes a little longer for the engine to reach optimal temperature. Check your Range estimate when you start out and check it again at the end of each trip. It will probably go up substantially as you drive.
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  #20  
Old 12-16-2013, 09:34 AM
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microswitch microswitch is offline
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Who knows the car better than anyone else ? The one that drives it. Period.
I understand the OP when He/She says " I have not drove the car in any way different than before". All the suggestion in here point to the canned answers for poor gas mileage. i.e. tire inflation, spark plug, O2 sensor etc etc but those instance especially the tire inflation account for maybe 1% ? And what about the case when the spark plugs are the culprit? I've never seen a car with bad spark plug run smooth, it normally have a bad idle or miss and then the SES pops out. But what you do when you loose about 20- 25% in your mileage and your car still run smooth ? I started to notice a bad gas mileage about 13 months ago. I never had a SES just the Average MPG on my OBC. Chalk it up to bad gas or driving habit although I have been driving 30 + years. But in the last 6 months. I have been getting SES.
My car is afflicted by a intermittent P0174. It comes and goes. Meaning after setting the code it will go away on his own for coming back later. I have seen my car steadily worsen gas mileage from 21 down to 16 and after a list of things I did trying to fix the intermittent SES, I'm back to 17. This is what I did;
1) Checked all vacuum hoses and replace the old one's
2) Re-checked all the CVV hose ( it was installed new 10,000 miles ago
3) new O2 sensor
4) removed and sent out injectors for re-building
5) Checked purge valve operations and vacuum
6) Fuel filter and regulator was changed 8,000 miles ago
7) checked DISA valve and replaced the o'ring
8) replace o' ring on dip stick tube
9) replaced caps on rear of intake manifold
10) Replaced o' ring on manifold distributor
11) Smoke tested the car 2 times both negative

And after doing all this I only gained 1 louse MPG.... You see in the beginning when I noticed a worsening of my gas mileage I had an error code it just was pending...... and I never seen it because it was intermittent, till the issue got worse to lit the SES. I bet the OP has my same issue He/She just does not see it unless has a scan and can read the pending code in which case I bet it would be a lean condition with lousy adaptation values.
It is a progressive thing like a cancer it lurks in the dark and when is too late it comes out saying/ : here I'm you see me ?? I only wish to know where the SOB comes from so I could plug that damn hole !!

But here is the the effect of it...... My adaptation value are very high 11.7% for the Long Term Fuel Trim. The short trim are negative at idle meaning I have no vacuum leaks but increase under load. Years ago there were two type of vacuum; Intake vacuum and ported vacuum. Intake vacuum was high at idle and low at high RPM; ported vacuum was low at idle but high at high RPM. Well at least for my car seems like if I have a leak is in the ported vacuum But we do not have ported vacuum in our cars or do we??? I have two friends with a 2003 530 and another with a 2001 525. They use independent mechanics because they are not comfortable with screwdrivers... complaining of an intermittent SES were told " Leave it alone, these cars are like this" They probably spent hours chasing this ghost on many other cars and do not want to waste any more time hence "Leave it Alone".. They are not complaining about gas mileage yet but I'm sure it must stink like some of us affected by this issue. Bringing the car to a dealer for a diagnostic is not a guarantee they will find the problem. The only other thing I have got left to do is to replace the 1) Disa and 2 ) MAF sensor then I would have replaced anything that would affect efficiency and gas mileage. Bad valve or cylinder leak? ... No my car runs smooth like a baby butt and runs great...

Sorry about the long post but i just wanted to give some food for thought to everyone who comes in here either to help or to learn about their cars. In my case I will try to learn and share my knowledge and experience for the benefits of other. And rest assure once I find the problem with my car I will have found a very common issue with with our beloved E39
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Last edited by microswitch; 12-16-2013 at 10:09 AM.
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  #21  
Old 12-16-2013, 09:48 AM
sxty8goats sxty8goats is offline
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One thing that often changes in the cold weather is idling the car to warm it up before you leave for school or work. If you are one of those that do this, you will see a drop in average MPG. Especially if your trips are short to begin with, Idling for 10 minutes before a 10 minute drive uses about 1/3 more gas than just getting in the car and driving without warming it up.
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  #22  
Old 12-16-2013, 12:23 PM
dvsgene dvsgene is offline
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Bottom line, if after searching for vacuum leaks, tune ups, E85 etc etc, and an E39 owner can't live with bad gas mileage, sell the car and get a 2013 car. They are designed to be fuel efficient for CAFE purposes.

Remember our cars were built in the years when gas were $1.50 a gallon not $4 a gallon.
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  #23  
Old 12-16-2013, 12:46 PM
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doru doru is offline
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My gas mileage went down the drain slowly but surely over the last 4-5 years.
And I know I have no vacuum leaks - all rubbers are new. I have a new MAF. The DISA is rebuild (but I tested the car with a brand new DISA - which I have as a spare - no dice). I have new injectors. I have new sparkplugs. The air filter is always changed. Tire pressure is checked periodically, and I haven't seen more than 1 psi difference between checks. The only thing that is "old" are the pre-cat O2 sensors - they have prolly 40k miles now (they were changed at 65K miles). Vanos seals replaced.

I used to have 21 mpg city driving (summer) and 18.5 mpg city driving (winter).

I use the same route to work for the last 10 years or so.

Now I'm at 17.5-17.8 mpg summer and 16 mpg winter.

It's NOT the winter gas, and it's NOT all that urban myth related to vacuum leaks, tire pressure, sparkplugs etc. It's something else, and I am chasing it, and I hope I will find it.

Just stop re-posting all that tire pressure, sparkplugs, vacuum leaks etc nonsense. Because something degrades. As far as I'm concerned, I strongly believe the automatic transmission unit might have something to do with it, but I have no hard evidence (yet).

Also, the OP lives in LA - is SoCal? If yes, they have no winter gas.........so re-think a bit.
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  #24  
Old 12-16-2013, 01:03 PM
bmw530ii bmw530ii is online now
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i cant just sell my car and get a brand new one. it just bothers me how im getting bad gas mileage even though i used to get better when i first got it a few months ago. i feel like im at the gas station every other day ( i only put 10 or 20 dollars at a time to make the car weigh less). when i first got my car i was getting over 20 mpg on the streets. when i made this post(about 2 months ago) i was getting 16, now im getting 13. i rarely ever drive on the highway. and yes i do live in socal. i also just wanted to note that i got new sparkplugs.

Last edited by bmw530ii; 12-16-2013 at 01:07 PM. Reason: grammar
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  #25  
Old 12-16-2013, 01:38 PM
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doru doru is offline
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Quote:
Originally Posted by bmw530ii View Post
i cant just sell my car and get a brand new one. it just bothers me how im getting bad gas mileage even though i used to get better when i first got it a few months ago. i feel like im at the gas station every other day ( i only put 10 or 20 dollars at a time to make the car weigh less). when i first got my car i was getting over 20 mpg on the streets. when i made this post(about 2 months ago) i was getting 16, now im getting 13. i rarely ever drive on the highway. and yes i do live in socal. i also just wanted to note that i got new sparkplugs.
This is a drastic mpg reduction. I would suspect in this case some torn rubber boots. If your mileage would go down ever so slightly over months, it's a different issue (like mine). I thought you experienced the very same issue.
If I were you, I would hook up a decent scanner and check for stored codes. You probably have a few, just waiting to pop up. The big rubber boot at the "Y" is a prime suspect, but all the other skinny rubber hoses can crack as well. The DISA will loose the seal around the intake, and will degrade to the point where one can loose the engine - the steel pin can come loose and ingested in the combustion chamber. Lastly, the O2 sensors if not changed. All the above will store some codes. The CEL will eventually go off one of these days in that case.

There were quite a few people reporting about bad mileage, with the above suspects taken care of. This is baffling. The O2 sensors go "lazy" after 100 k miles, then eventually they get useless. All rubber hoses get "cooked". Mine "looked" OK, felt OK, but when I tried pulling on them to replace them, they started to elongate like chewing gum. The big rubber boot at the "Y" had holes developing. The rubber caps started to crack. The DISA pin was barely hanging in, and the seal was gone. All this at 100 k miles.
If after all this, you still have bad mileage, something else is playing tricks, and I suspect the tranny starts to have different shift patterns (ever so slightly, but enough to play with the mileage).
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TMS underdrive pullies - Stewart WP - PSS9 - Beisan Vanos seals - Zimmerman cross-drilled & Akebono Euro - Deka 649 MF - 55w HID headlights - 35w HID foglights - Hualigan double din - ACS (rep) alu pedals - Euro central storage console - Breyton Magic Racing staggered wheels - M5 bumper - M5 steering wheel - Tint
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