# Improving fuel economy



## Thomv (Jan 27, 2012)

Re-tuning the computer has been discussed for more power, but has anyone looked at it purely to increased mileage. I am starting a 110 mile round trip commute with my 35d which gets excellent mileage. (28 on the road). But why not be greedy? Can it be better. Got plenty of power. 

Thks in advance.


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## KeithS (Dec 30, 2001)

Carefully watching cause and effect for well over a year, I believe I have a handle on what impacts MPG of the 335D. Using highway driving under optimum conditions (flat roads, less than 75 MPH, ambient temp about 70 but NO AC usage), I achieve 40 MPG. These are the factors that reduce that amount.

The EGR program update lost 2MPG (That has been fixed with a later update)
A/C uses 2 MPG
Each 10 degree drop in ambient temp temp loses 1 MPG
18" wheels may lose 1 MPG or so (I have 17's so cannot verify) 

As far as reducing power, just make believe there is an egg between your right foot and the power pedal!


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## d geek (Nov 26, 2008)

KeithS said:


> .... just make believe there is an egg between your right foot and the power pedal!


^^^This is the most effective mod for maximizing fuel economy in any car


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## GreekboyD (Jan 25, 2012)

Leave the extra weight of the wife and kids at home.


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## Snipe656 (Oct 22, 2009)

Lighter wheels and tires might help. I know a lot of people claim increases in mpg with their winter tire setups.


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## ChasR (Aug 29, 2012)

The Evolve folks claim a 10% improvement in fuel efficiency with their tune. If so, with the miles I drive, the tune will pay for its self in a couple of years. I'll know later this week.


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## F32Fleet (Jul 14, 2010)

Program engine to run as a 4cyl while on hwy.? I6 engine mated with 6spd. The 335d is the best you'll get out of that.configuration.

Sent from my MB525 using Bimmer App


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## Axel61 (Mar 10, 2011)

better yet, STOP flooring the bastard on the road and drive like Grandma!!! LOL


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## kungpao (Oct 10, 2012)

but... but.. it's fun to flog it!

Driving like a Grandma didn't help in my x5. I found that driving normally for me got better mileage than trying to watch the gauge. Course it helps that my daily commute averages between 55-65mph so i get the higher range of the fuel economy rating


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## robster10 (Oct 8, 2012)

Do most of you check tire pressure? Although some use nitrogen, if you use reg air tire pressure can make a difference. Keep it at specs. I'm in Canada so outside temps fluctuate with the season, so even with runflats they may look ok but if low will create more rolling resistance. Experimented with higher pressure & got better mileage but if you put in too much handling characteristics change.


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## BB_cuda (Nov 8, 2011)

*Electrical loads play a role*

I have experimented with the seat warmers and rear defogger while cruising on a 300 mile trip home. The trip normally yields me ~38 mpg going 70 mph. Using these devices for about 50 miles, i saw some drop off but guessing it was about 1-2 mpg. The alternator produces this current needed and think of it as a higher load on the alternator requiring a little more torque (on the pulley itself) to produce the higher current. I have heard that NASCAR racers shut down the alternator at the end of a race and run off the battery to get that little extra uumph. I thought it befitting to mention this on opening day of the season . DAYTONA 500


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## Flyingman (Sep 13, 2009)

Thomv said:


> Re-tuning the computer has been discussed for more power, but has anyone looked at it purely to increased mileage. I am starting a 110 mile round trip commute with my 35d which gets excellent mileage. (28 on the road). But why not be greedy? Can it be better. Got plenty of power.
> 
> Thks in advance.


Thomv, I recall when looking into some tunes that they had different maps you could choose from. Some were for better economy vs power. You could tweak it all over the place (or map).

I think variable geometery turbos would prove to be the most beneficial. You also need to understand that these cars are tuned to produce the lowest emissions, which may conflict with most efficient or best power out.


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## 335dFan (Nov 8, 2012)

*VAC Motorsports Intelligent Diesel Control Module (335d / 535d/ X6d / X5d etc)*

VAC Motorsports has a piggyback unit VAC - Intelligent Diesel Control Module (335d / 535d/ X6d / X5d etc) that you can order either as increased performance or increased MPG. I do not own one, but am considering it as an alternative to the JBD, although it is more expensive.

http://store.vacmotorsports.com/vac...rol-module-335d--535d-x6d--x5d-etc-p2081.aspx


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## Snipe656 (Oct 22, 2009)

According to a user on here the VAC does increase the mpg some as per their pen and paper calculations. I have a used JBD that I will be putting up for sale soon, once I get around to taking a picture of it. I never used it but don't think from reading on here or from way back when I talked to the original owner that it increases your mpg any.


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## robster10 (Oct 8, 2012)

BB_cuda said:


> I have experimented with the seat warmers and rear defogger while cruising on a 300 mile trip home. The trip normally yields me ~38 mpg going 70 mph. Using these devices for about 50 miles, i saw some drop off but guessing it was about 1-2 mpg. The alternator produces this current needed and think of it as a higher load on the alternator requiring a little more torque (on the pulley itself) to produce the higher current. I have heard that NASCAR racers shut down the alternator at the end of a race and run off the battery to get that little extra uumph. I thought it befitting to mention this on opening day of the season . DAYTONA 500


Unlike the A.C. compressor I believe the alternator always spins no torque change. The compressor has a clutch on it and when not on just spins the pully (friction loss) but when A.C. is turned on clutch engages and creates an additional load on motor reducing mileage. As for nascar thay may have something that disengages the pulley line completely. I know they sell underdrive pulleys witch spin components at a different rotation level wich creates more hp/torque but not really it just reduces the drag on the motor.


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## d geek (Nov 26, 2008)

robster10 said:


> Unlike the A.C. compressor I believe the alternator always spins no torque change. ....


Sure it does. The higher the electrical load the more force it will take to turn the alternator. Especially after a cold start when the starter and glow plugs have depleted the battery and it is sucking down the current. No work is done for free


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## Flyingman (Sep 13, 2009)

robster10 said:


> Unlike the A.C. compressor I believe the alternator always spins no torque change. The compressor has a clutch on it and when not on just spins the pully (friction loss) but when A.C. is turned on clutch engages and creates an additional load on motor reducing mileage. As for nascar thay may have something that disengages the pulley line completely. I know they sell underdrive pulleys witch spin components at a different rotation level wich creates more hp/torque but not really it just reduces the drag on the motor.


Don't you wish! The more current produced the more torque translated onto the generator rotor which is in turn driven by the pulley and fan belt. It will definietly cost you some MPG to run more electrical equipment, but it would not be nearly as much as the A/C compressor.


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## Pierre Louis (Oct 23, 2011)

I believe higher cetane fuel may improve fuel economy. I don't know if putting in aftermarket additive for this would be a good idea only because of side effects on the rest of the engine/pollution control system. BMW is on record not recommending aftermarket additives.

It might be a good thing to try different sources of fuel to see which will give the best economy, since apparently higher cetane also produces less soot and will cause less depletion of the DEF.

PL


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## robster10 (Oct 8, 2012)

*better mileage.*



Flyingman said:


> Don't you wish! The more current produced the more torque translated onto the generator rotor which is in turn driven by the pulley and fan belt. It will definietly cost you some MPG to run more electrical equipment, but it would not be nearly as much as the A/C compressor.


At idle & in park turn on your rear defogger & heated seats, try this again *seperately* by turning on the AC. Watch as the rpms drops for the later. There's more current drawn for the first two than most other equipment in the car, but very insignificant change of torque draw. That is why some makes also dropped pulley style water pumps for electric motor driven water pumps, no torque drawn away from crank pulley.


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## Snipe656 (Oct 22, 2009)

That does not disprove what the others are saying in that some added fuel consumption happens with added load to the electric system but nothing to the level of adde fuel consumption a belt driven compressor does. 

Switching to an electric water pump for added fuel economy makes sense. A belt driven always has a load and always runs. Electric only needs to run when needed and the added load to the alternator will also take less "engine power". 

I personally find it surprising this could be measured via mpg. I'd think it would be very minimal.


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