Latest issue had some they tested and some they had experts analyze. The myths:
1. You save gas by coasting in neutral versus leaving it in high gear and taking your foot off the gas. You don't because if you coast in gear the engine knows its rpm is faster than idle rpm and it basically shuts off fuel delivery whereas the engine uses more gas than idling in neutral. Makes sense but I didn't know that.
2. Driving with AC on/windows closed uses less gas than AC off/windows open. The diff was less at highway speeds but maybe 4% more gas with AC on.
3. Overinflating your tires means better mileage. Not. (But underinflating gets worse.)
4. There's no effect of roof racks on gas mileage. Roof racks do in fact lead to worse mileage, even just the bars without the carrier installed. In fact the carrier didn't lessen mileage much compared to the rack bars themselves.

 

Interesting facts. I don't know if the 1st gens have this, but my 09 has an up-to-the-moment MPG display in the OBC. If you're taking off from a light, it dips down; if you are coasting down hill (in gear or out of gear), it reads 99.9mpg.

As for the second fact, I remember seeing that on MythBusters. The difference was negligible (and if I recall, they were testing it with SUVs).

Thanks for the info!

 

I would argue the first one when driving on hilly roads. The engine-breaking effect going downhill kills the momentum you can build up for the next uphill. For mild hills, I might have to have the gas on a bit going downhill, whereas in neutral you cruise until the road levels out. I'm not a Mini owner (just a fan ,and shopping), but I assume all stick-shift cars act this way like mine.

I'm surprised the roof-rack one is a myth... I just assumed a roof-rack with the horizontal crossbars would kill 1-2mpg.

 

The less mpg with roofrack isn't a myth, but I was surprised it decreased mpg by about 3-4% (highway) no matter if you just had the bars or the carrier. I had rack bars on my 2 jeeps and never used it.

 

what about higher octane gas and gas mileage.

i know higher octane deals with reducing knocking on high perfomance vehicles or something and does not affect your mpg. can anyone explain this in english?

 

Higher octane has more enegy (more cowbell!) than 87, so mileage is better. Probably not enough to compensate for the higher price, which is why there's no reason to use it in cars that don't recommend/require it like the Mini.

 

there are numerous numerous articles online stating that higher octane gas does NOT increase mpg and does NOT increase HP. i think all that is total BS but watever...

It seems that unless your car demands higher octane, you may be getting a some increase in HP and MPG... but if your car doesnt require higher octane gas, i dont think it improves anything.

http://www.wanderings.net/notebook/M...sWorthTheMoney
Does High Octane Gas Improve Gas Mileage?

No. Unless your car is explicitly designed to run on high octane gas1 (it's rare, read your car's manual), using a high octane gas will NOT give your car better mileage. That's because the rating refers to how much energy it takes to ignite the gas, not directly to how much energy the gas puts out.

Does High Octane Gas Give More Power?

No. Unless your car is explicitly designed for high octane gas (see your car's manual), using a high octane gas will NOT improve the power output of your engine. Again, the octane rating relates to how much energy it takes to ignite the gas, but NOT directly to how much energy the gas puts out


meh... watever

 

Who told you this? My MA told me to use premium. The mechanics at the MINI dealer also said to use it. The owner's manual for my MINI says to use premium. The gas cap door says use minimum of 91, which is premium.

 

I am willing to bet they did limited research. You can't come to these conclusions by only testing one or a few cars either.

For instance take 1 point: "over inflating tires does not increase gas mileage." How many different tire brands did they research, does this apply to snow tires, all seasons, race tires? How about wide tires or narrow tires or low profile tires? What do they consider over inflated is it filling the tires cold to the recommended air pressure or hot tire inflation?

Go out and fill your tires to the recommended air pressure 33 lbs. and drive/ let off the gas. Then fill your tires to 40 lbs. You can feel the decrease in rolling resistance and improve gas mileage.

 

In other words, high octane gas burns slower than low octane gas.

 

I believe MINIs are designed to run on higher octane...both for power and mpg. The benefits may be small (especially in R56), but that's what the manufacturer recommends.

I also wonder how applicable C&D's coasting info is to MINIs. I think I read that w/ MINIs the injectors are shut down either way and, as has been said, coasting yeilds more momentum.

 

on older carburated vehicles would #1 hold true to the myth?

 

Maybe not. It said cars from the mid-90s on used virtually no gas coasting in gear. Probably all fuel injected.

I think they tested one car on a closed course, not multiple tires/conditions, etc. The point is you can only decrease rolling resistance so much, and overinflating tires just makes you hate the ride. Makes sense to me.

 

They said that in neutral foot off gas the injectors can't be shut down (that's idling at a stop light). Car in gear coasting the car knows the it is moving, shuts injectors off. Makes sense.

 

All R56s have direct injection (DI/FSI) engine -- they are certainly designed with premium fuel in mind. Yes the ECU + sensors can handle 87, but that's as good as feeding our kids with junk foods.

 

My boys did fine on junk food (I assume that going through a stack of frozen pizzas a week qualifies as junk food ). The aircraft carriers have healthier food but I'm not sure how fast it goes.

 

Maybe a dumb question....but if the injectors are shut off when you're coasting in gear...what is firing? Wouldn't the exhaust go silent?

 

Nothing, the wheels are keeping the engine turning. I've never listened to the engine, but the on board computer pegs the MPG when you do that. When you coast in neutral the on board computer shows some MPG, the engine has to keep itself turning.

 

Ok I can understand that concept....but I guess I'm just confused as to what sound I'm hearing then. The R56 exhaust is louder on engine braking than accelerating sometimes. Sounds wonderful coming out my Invidia...hard to believe that there is no explosions of any sort going on in there....

 

There was a Mythbusters episode where they did the A/C on/off and windows up/down. They got better mileage with the A/C on.

And on another note they got better mileage in a truck with the tailgate on (myth being no tailgate = better mileage). So there goes that myth of keeping the MINI hatch open for better mileage!

 

The problem with more momentum while coasting downhill is that the greater downhill speed means you spend less time going down the hill and less time off the throttle. Given air drag goes up with the square of velocity and that waste products of rolling friction, like heat and noise, go up with speed, this would seem to favor maximizing the time spent coasting downhill at a lower speed.

For carburetors, my experience is coasting in neutral doesn't work. At idle, the throttle butterfly valve is almost completely closed and limits the flow of air to a minimum. Increasing the engine speed increases the number of intake strokes per minute, plus increases the velocity of the piston during the intake stroke. However, because the piston is drawing against the restriction of the closed throttle valve, the pressure seen inside the intake manifold reduces at a much faster rate than the air flow increases. While this small increase in airflow would increase the fuel flow, the savings would very, very small.

For fun, I used to coast my '66 VW Bug down Highway 9 between Felton and Los Gatos, which was about a 15 minute downhill run. When it came time to fill the tank, I never saw a mileage difference between coasting and not coasting.

 

With my 71 bug the best way to increase MPG was to get behind a semi. Which BTW Mythbusters proved to be completely true, but dangerous.

 

When you coast, the a/f goes lean, to reduce emissions.

The injectors never shut off if the engine is running.

 

Ok this was my point....thank you.

I knew they must not be completely shut off, but I've heard that so much on here.

 

NAM has alot of good info from alot of knowledgeable people, but it also has alot of crap info from alot of misinformed people.


Use your discretion to decide what to believe.