Tips for Improving Mileage, Most of Which Simple

[christophbmw]

The condition of the O2 sensor is a HUGE factor.  It fully determines the short- and long-term fuel trim settings.

I always get crappier mileage on my drives to Santa Barbara because of the mountains i have to pass through.  They really kill it.  I take 101, and it is a LOT better than 5, for sure.

i took 101 also, my o2 sensor is about a year old (bosch). i still cant believe i got 30 mpg! ive never got milage that good, i only got 27.7 from salinas to paso robles because i was doing 110mph for 5 minutes straight (at one in the morning). did pretty good for being under load at 4800rpm's for five minutes straight!:D probabally the only time ive been over 100mph (in a car) for more than 30 seconds. but then again over in europe that's what its made for.....the autobahn.

around town i usaully turn out 24mpg, whos running a 3.91 or 3.64 diff? i want to uprgade to an LSD and have been thinking about getting a lower gear ratio......4k rpm's at 80mph doesnt do it for me....to noisey

Just take a high quality Fluke Multimeter or equivalent and measure some old corroded vs. new. You'll see what I mean.

i used to have problems on my M10 with corrosion/bad connection's, you wouldnt believe the problems it causes.....i thought you where talking about thicker ground cables.

[tjts1]

This weekend I took the 318i for its first long (200 miles) highway trip to Sacramento and filled it up with 87 octane (I know I'm going to hell for that one huh) immediately before and after the trip. The whole way I tried to keep it around 80mph (3800 rpm) with the occasional sprint to pass and about 10 miles of city driving. Temperature varied from 60F (morning in the Bay Area) to 96F (afternoon in Sac). The car has an electric fan conversion, manual steering, non functional AC (soon to be fixed I hope) and missing front air dam. At the end of the day I managed 30.5 mpg. Not bad in my opinion for a car that was rated by the EPA at 20 city, 25 highway. In normal mixed city/highway local driving around here, I managed between 23-27mpg depending on how often I abuse it.
This 4.1 LSD is a pain in the ass on the highway so in Sacramento I picked up something more soothing to the ears.

I'll install it this weekend and report back after a few more highway trips. Don't get too excited. I won't be selling the 4.10 LSD just yet In case I don't like the 3.64.

I used some regular cardboard box tape to cover up the brake cooling ducts and the missing fog light plug on both sides. I need to come up with a cheap solution for a new air dam. You don't really need all that brake cooling on the highway. Every little hole you can plug up will reduce drag. Also removed the wipers. I won't need them again until October or November. Keep them in the trunk just in case.

The goal is 40 mpg on the highway without changing my driving habits and still enjoy occasional autoX with wheel and diff swap.

[Alpine003]

filled it up with 87 octane (I know I'm going to hell for that one huh)

At the end of the day I managed 30.5 mpg.

Every little hole you can plug up will reduce drag. Also removed the wipers.

The goal is 40 mpg on the highway without changing my driving habits and still enjoy occasional autoX with wheel and diff swap.

Good thing you don't have knock sensors or they might have pulled back timing on 87oct resulting in lower mpg.

As far as holes, E30 shape is general is not very aero so it's sort of tough. I guess every bit can help somewhat. You should look into cutting thin ABS sheets and epoxying behind the grill area where it doesn't interupt flow to the radiator. The Euro-Grills already have some additional block off plates built into them from behind but would be a good mod for US grills. I have done this already.

In addition to wipers, I think the side mirrors can attribute a little to the drag.

As for 40mpg, that's a little tough without making too many performance sacrifices. I suppose if you got the tallest and skinniest tires, got a 3.25 rear end and lowered your car then maybe close...

[tjts1]

At part throttle I don't think a knock sensor would make any difference. My volvo 960 for example has 10.7:1 CR, 4 valve head, producing 200hp from 3.0. The Motronic 1.8 on that car utilizes 2 knock sensors and can advance and retard timing for the front 3 and rear 3 cyls separately using COP ignition. With the diagnostic software loaded on my lap top I can monitor and record ignition timing among other parameters. On 87 octane it doesn't begin to retard timing until 70% throttle. On 91  octane it retards timing around 90% throttle in hot weather (80F+), and no retard  at all at anything less than 60F. Anywhere less than 70% throttle input in closed loop, it runs the exact same timing curves on 87 and 91 octane. It also gets slightly better fuel economy on 87. Factory recommends minimum 91 octane at all times. I think its BS. If I'm just cruising down the highway at part throttle for hundreds of miles on end, I think its safe to use 87 octane. For spirited driving I still give it 91.

I'll take a look at the grills. Thanks for the tip, but I'm going to have to keep the mirrors for safely reasons. I'm not that crazy.

I'll see what happens with the 3.64 and report back. I think its the tallest small case diff available in the US. I guess I could get a 3.45 from a 318ti 5 speed but I really don't care that much and I don't want to be driving a total slug. 4th gear + 3.64 = 5th gear + 4.10. I don't mind down shifting once in a while.

[sheepdog]

At part throttle I don't think a knock sensor would make any difference. My volvo 960 for example has 10.7:1 CR, 4 valve head, producing 200hp from 3.0. The Motronic 1.8 on that car utilizes 2 knock sensors and can advance and retard timing for the front 3 and rear 3 cyls separately using COP ignition. With the diagnostic software loaded on my lap top I can monitor and record ignition timing among other parameters. On 87 octane it doesn't begin to retard timing until 70% throttle. On 91  octane it retards timing around 90% throttle in hot weather (80F+), and no retard  at all at anything less than 60F. Anywhere less than 70% throttle input in closed loop, it runs the exact same timing curves on 87 and 91 octane. It also gets slightly better fuel economy on 87. Factory recommends minimum 91 octane at all times. I think its BS. If I'm just cruising down the highway at part throttle for hundreds of miles on end, I think its safe to use 87 octane. For spirited driving I still give it 91.

I'll take a look at the grills. Thanks for the tip, but I'm going to have to keep the mirrors for safely reasons. I'm not that crazy.

I'll see what happens with the 3.64 and report back. I think its the tallest small case diff available in the US. I guess I could get a 3.45 from a 318ti 5 speed but I really don't care that much and I don't want to be driving a total slug. 4th gear + 3.64 = 5th gear + 4.10. I don't mind down shifting once in a while.

I would NOT go with a 3.64 rear end. The car needs the 4.11. With the A/C on, you will want that 4.11


If you cannot afford the 91 octane, get rid of your car.
These are not Hondas you can abuse and treat like crap, it will bite back. Maybe not today, but soon enough. These cars do not adjust for lower octane like newer cars.


By the way you saved less than $3 on your tank of gas by risking a motor that costs as much as your car (for a rebuild), and one not known for liking poor maintenance. You probably lost a lot of that by the lower mileage you got. My old Celica worked out cheaper to use 91 since it got such better mileage.

Like I said, if you cannot afford premium, sell the car.

[sheepdog]

Good thing you don't have knock sensors or they might have pulled back timing on 87oct resulting in lower mpg.

As far as holes, E30 shape is general is not very aero so it's sort of tough. I guess every bit can help somewhat. You should look into cutting thin ABS sheets and epoxying behind the grill area where it doesn't interupt flow to the radiator. The Euro-Grills already have some additional block off plates built into them from behind but would be a good mod for US grills. I have done this already.

In addition to wipers, I think the side mirrors can attribute a little to the drag.

Have you actually looked at the numbers on the aero of the car?
Yes, it is shaped like a box, but you would probably be surprised how many cars are no more aerodynamic than these. They were quite ahead of the curve despite how they look.

The other recommendations are good though.

[tjts1]

By the way you saved less than $3 on your tank of gas

What can I say, I live dangerously. That $3 bought me a hot dog and a coke for lunch on Sunday. But honestly I would love to see at least one M42 that died because of low octane abuse on this forum. This one has been on a steady diet of 87 octane for the last 139k miles. Why would I do anything different? Come to think of it, why would anyone offer aftermarket chips to take advantage of high octane gasoline if 87 will kill this engine? I'll let you know when I kill mine.

I don't have time to argue about every one of your points but I have a nice little before and after the diff swap comparison test lined up. You crack me up

[Alpine003]

Have you actually looked at the numbers on the aero of the car?

Yes but not that spectacular but decent for the time. There were still a good amount of cars back in the day as early as the mid 80's that had equal or better aero than this car.

Damn, I think the $3 saved was worth that hotdog. That's making me hungry.

[christophbmw]

we have a drag coeficient of .28 which is quit low. i think its actully lower than a new civic (because our car is soooo much smaller). anyways i think the E30 is aerodynamic, have you seen a hummer latley? or better yet the 60% of our selfish population driving huge ass cars? id say were in the the top 10% of the aero dynamic spectrum.

and i hate to be the messenger here but 87 octane will ruin your rod and crank bearings over time. ive seen it happen many times (ok only twice) on the M42. one of those motors being my own because the previous owner put 87 in the car.....just my 2 cents, these motors are only bullet proof if used correctly....sort of like a condom.

[tjts1]

we have a drag coeficient of .28 which is quit low. i think its actully lower than a new civic (because our car is soooo much smaller). anyways i think the E30 is aerodynamic, have you seen a hummer latley? or better yet the 60% of our selfish population driving huge ass cars? id say were in the the top 10% of the aero dynamic spectrum.

and i hate to be the messenger here but 87 octane will ruin your rod and crank bearings over time. ive seen it happen many times (ok only twice) on the M42. one of those motors being my own because the previous owner put 87 in the car.....just my 2 cents, these motors are only bullet proof if used correctly....sort of like a condom.

.28 drag? I find that a bit hard to believe. Do you have a source for that information?

I don't see the connection between octane and bearing wear. Are you sure it didn't have more to do with with the combination of cheap oil, high revs and long oil change intervals? Your pistons and valves will get burnt by low octane gasoline long before any bearing damage can occur.

[christophbmw]

knocking is extremely bad on the lower end, the lower end of the M42 is very strong but it can only take so much. you have to rmember: the resiprocating mass is pushing extremely high g-forces, if those g-forces arent controlled in a smooth matter stuff will fail over time.

i got the drag readings from the "3-series companion" book i forgot the author, i have it at home....very reliable source. how do you find it hard to believe? the E30 is a very small car, the enemy of aerodynamics is size.

[sheepdog]

I think I remember seeing .33, I wish .28.

[tjts1]

i got the drag readings from the "3-series companion" book i forgot the author, i have it at home....very reliable source. how do you find it hard to believe? the E30 is a very small car, the enemy of aerodynamics is size.

The enemy of aerodynamics is sharp corners and air gaps, not size. Coefficient of drag (CD) represents a ratio of the total amount of drag produced by a vehicle divided by its total frontal area. This ratio allows you to compare the aerodynamic efficiency of two different size vehicles. So for example a 2006 Mercedes S class has a CD of .26 while a 2001 Honda Civic has a CD of .36. The S class is more aerodynamic than the Civic despite being much larger. I suspect the E30 is somewhere between .35 and .40. But thats just a guess until i find something more reliable.
Source
http://en.wikipedia.org/wiki/Drag_coefficient

After looking at the price difference between 87 and 91 octane ($3.31 vs $3.50) and considering the low fuel consumption (32mpg on the latest fill up) I might start using 91 octane more often. But I still think its pathetic that BMW didn't fit a knock sensor on this engine in 1991. Volvo was installing knock sensors on all its US bound cars by 1988.

[sheepdog]

I just looked it up, 318IS is .33
The M3 was .32.

For comparison:
1991 Acura NSX .32
2000 Audi TT coupe .32
1991 Ferrari F40 .340
1996 Ferrari F50 .37
1996 Honda Civic .34
1998 Honda Accord .34
2000 Jag S-Type .32
1997 McClaren F1 .31
1999 Porsche 911 .30
1998 Toyota Camry .34
2000 Toyota Prius .29
2004+ Toyota Prius .26

[D. Clay]

we have a drag coeficient of .28 which is quit low. i think its actully lower than a new civic (because our car is soooo much smaller). anyways i think the E30 is aerodynamic, have you seen a hummer latley? or better yet the 60% of our selfish population driving huge ass cars? id say were in the the top 10% of the aero dynamic spectrum.

I have been under the impression that drag coefficients applied to the shape and were independent of size.
i.e. drag coeficient * frontal area = aero drag.
I may be wrong here but that's nothing new.