Gas Mileage

[crazycanuck]

Anyone know how accurate that Mileage computer is? I filled up and it said 480km (Canadian). I drove it tonight and it started out at 480 and after 7 minutes of driving, it said 420kms!!! And no, I didnt drive 200 km/hr... what gives? Is it just the gas sloshing around and it trying to recalculate on the fly?

The gas needle hasnt moved off of Full yet.

[njjuliano]

It averages out on driving behavior. On fill ups, I can see from 200 to 350 miles left, depending on current and past driving behavior.

[Peaty]

I found it's not all that accurate compared to really calculating the MPG's It tends to be on the optimistic side.

[crazycanuck]

Interesting since I had a 2001 Pontiac Montana that had a trip computer. It was pretty darn accurate with its calculations and how much gas was used. I would say +-20km over a tank and +-5 litres over 100 litre fillup. 26 gallons for you americans :-)

[Magic Marker]

I don't even bother with the MPG count. It's a B9 that takes Premium gas. We just drive it and fill it up when necessary.

We have a Civic when we need to sip on gas.

[crazycanuck]

I hear ya, I just wanted to make sure I didn't have something defective.
It costs 1.16 per liter for 91 Octane. Approx 4 liters to a gallon, thats about
4.64 per gallon here. Don't even ask what the 93 octane costs!

[Magic Marker]

I hear ya, I just wanted to make sure I didn't have something defective.
It costs 1.16 per liter for 91 Octane. Approx 4 liters to a gallon, thats about
4.64 per gallon here. Don't even ask what the 93 octane costs!
The premium here in NJ is 93 octane. I don't think I've ever seen 91 octane before.

[crazycanuck]

most stations here carry 87 89 and 91, our local sunoco carries
87 89 91 and (my mistake) 94 not 93.

The subaru manual recommends 91.

And its 1.21 per liter for 94. Thats almost $5.00 per gallon

[battlecat]

how many miles does everyone get per tank approximately?

[ralliartist]

I get about 320-350 miles per tank and I put mid-grade 89 octane in my tank. I live here in Nebraska and the mid grade has E-10 ethanol added. So I'm sure I'm not hurting my vehicle.

[ninefourteener]

Ironically enough.... nowhere on my Tribeca does it say that it calls for premium fuel. Although here in Utah, the best you can get is 91.

Nevertheless, we just had our first fill-up. We calculated the total gallons divided by the total miles we've driven..... both city and highway.

We averaged 21 mpg...... AVERAGE.

I thought it was only supposed to get 21 on the highway. Not complaining.. just surprised.

Oh yea.... and that was on el-cheapo 85 Octane. We filled it this time with mid-grade (87) to see if we can justify the price increase.

[Magic Marker]

Ironically enough.... nowhere on my Tribeca does it say that it calls for premium fuel. Although here in Utah, the best you can get is 91.

Nevertheless, we just had our first fill-up. We calculated the total gallons divided by the total miles we've driven..... both city and highway.

We averaged 21 mpg...... AVERAGE.

I thought it was only supposed to get 21 on the highway. Not complaining.. just surprised.

Oh yea.... and that was on el-cheapo 85 Octane. We filled it this time with mid-grade (87) to see if we can justify the price increase.
Sounds good. We've put in 87 once. On the highway, no difference. But for off the line, 87 made it feel sluggish.

[kmartin]

Ironically enough.... nowhere on my Tribeca does it say that it calls for premium fuel.

Premium was recommended only for the '06 and '07 models. They updated the engine for '08, and no such statement was needed.

Also, although the mileage appears to be different in '08, the actual EPA standards were tweaked in 2007 (for '08 models), and the mileage is really pretty much comparable, just on a slightly different scale.

-Karen in AZ-

[b727plumber]

Ninefourteener,

Here in Colorado, reg is always 85 octane. The manual calls for a min of 87. Should we be using the mid-grade 87 and pay 10 cents more per gal? I've been getting mixed answers on this topic!

All you high altitude owners, please chime in!!!!

[snork]

Seriously? Reg is 85 octane? On the entire east coast I've never seen regular being less than 87...didn't even know there was an 85:Dunno:

I can only guess maybe the lower octane is better at high altitude, but I've honestly never heard anything about that.

On the east coast, regular is 87, mid grade is 89, and premium is 91...some brand stataions do 93 octane too rather than 91. A few Sunoco stations around even offer ultra-premium 94 octane:eek:

edit: forgot to mention about our mileage. I agree that the mpg meter is optimistic, in my experience it's about +2 mpg from what I calculate (mileage/fuel filled). So far the worst I've scene is about 16 mpg will all city driving and 21 on a 150 mi drive up to CT + about 50 miles of local driving. I've yet to do a full tank of highway cruising, but I can't imagine it'd go any better than 22/23. Also so far I've only put in regular 87 octane.

[Magic Marker]

So far running on 89 for the past 3 fills. No noticable difference in performance over 93.

[ninefourteener]

Well, we have yet to fill up for a 2nd time.... but we'll see what the mieage is when we do.

Here, there's 85, 87, and 91.

In St. Louis... I could get 87, 89, 91, and 93.

Although there is a place in town that sells 100 Octane race fuel..... for almost $7 per gallon.

I put 1/2 tank in the WRX once. Yes, it made a difference, but I can't justify the price unless I'm headed to the track.

[b727plumber]

Ninefourteener,

Are you running with 85 octane?

Thanks!

[ninefourteener]

I was.... we averaged 21mpg both city and highway.

We filled up with 87 this time.... we're going to calculate mileage and see if the difference in price is worth it.

[ralliartist]

took a 1000 mile road trip about a month ago. AVERAGED 24mpg on the highway. Was REALLY surprised. I got about 380miles to a tank. GO SUBBY!

[SubieTribeca77]

Just wondering if the Nav screen indicates that there's range of 40 miles left, how accurate is it to empty, when the gfas light first goes on?

In previous subbies I've had needle to help me gauge how low on E that Im actaully approaching... with this digital meter its alittle harder... Any thoughts?

[snork]

Yeah, I'm not a real fan of the "digital" gas guage neither...just something I don't trust about it;)

Anyway, I've never put more than 15 gallons in ours (16.9(?) gallon tank) after "pushing it" with the gas light on. So in my belief, you got about 3 gallons left in the tank when the light first comes on. I think the range mileage is set to leave you with about 1 gallon left in the tank so you don't litterally leave yourself high & dry.

[SubieTribeca77]

Thanks, thats what I thought. I calculated about 50 miles left but had to ask.
I suppose I can always take an empty container and find out for real! hahaha

[ozeguy]

Well, an EMPTY container won't do you much good if you run out of gas. Better take a full one :lol:

[jonnyk]

unfortunately, I can't properly do the conversions, but with dashes instead of miles left, and no lines on the gauge, I put in 57 1/2 liters of a 60 liter tank, approx, leaving me with a whopping 2 1/2 liters left, about 1/2 a gallon?

I don't know why I do that to myself!!:lol:

[ozeguy]

jonnyk, it wasn't quite as risky as you thought, because the tank holds 64 litres, not 60, so you had 7 1/2 litres left, or nigh on 2 US gallons, or 1 2/3 Canadian (imp.) gallons.

At the usual 10 litres per 100 km that I get on the highway, you probably could have driven from St. Thomas to London & back, before having to get out & push! http://www.sb9t.com/forums/images/icons/icon12.gif

Still scary though, when those dashes show up, isn't it?

[Vagit]

Here is mentioned about gasmileage of 3.6L Tribeca http://www.car-or-car.com/SUBARU/SUBARU_TRIBECA_2008_1_1.html

[y1der]

you will always (well most always) get better gas mileage on lower octane gas :)

[GREEKBOY]

Can I do somethink for the little fuel tank of my beca?
65 liters it is not enough for long trips...
I can bolt on another fuel tank?
My mercedes slk 200 has option for bigger tank (80lt) if I want it...why not and my beca...

[immortal_suby]

And the 2010 outback holds 18.5 gallons and gets better mileage. Kinda disappointing how poor the range of the tribeca is.

[drbrousters]

"you will always (well most always) get better gas mileage on lower octane gas"

I've heard this about low octane at higher altitudes, but never "always."
My personal experience is that, in my '06 Tribeca, 91 octane gas is 2mpg better than 87 octane...but...Premium is recomended for mine...due to the compression ratio which is higher in the 3.0 than the 3.6. Comression ratio is also lower at high altitude which is what causes the reduced need for octane.

[GREEKBOY]

Here we have only 95 octane and 100+ octane but the ''gas mileage'' is very bad for beca..
I hope subie gives boxerdiesel for tribeca....

[SimonD]

I can't tell the difference in gas mileage between high and low octane on the Tribeca but my Impreza definitely gives an extra 15-20 miles from a tank of 98Ron vs 95Ron.
I've found this with other cars in the past that forced induction engines respond better to higher quality fuels than normally aspirated.

As for the fuel tank, I've noticed that filling the last 8 litres/2 gallons takes a lot of time and patience. My wife just fills until the pump clicks off and rarely gets more than 20 miles before the first bar on the fuel gauge goes out. If I brim the tank we usually get 70 miles or so before losing the first bar. This makes quite a difference in the number of fuel stops on a long drive.

Lastly, the "miles to go" indicator on the computer seems pretty accurate. Other cars I've had would do at least 20-30miles after the computer says empty. I've run the Tribeca down to 10 miles to go in the past and subsequently filled up with over 60 litres of gas (in a 64 litre tank!). I will not be taking chances with the fuel computer in the future!!!

[drbrousters]

Here in the states, overfilling your tank ("brimming") can lead to damage to the emissions system. Many people are unaware of it, but it's true. Bad enough to have to have it on the vehicle; repairing it is even worse.

I've found the gas guage and gas mileage indicator to be, at best, spotty in their accuracy. I even find conflict between the trip meter and odometer. I just fill it when I start to get nervous.

Not sure what "Ron" refers to. Can you enlighten me (us)?

[SimonD]

What part of the emissions system is affected by overfilling? It does say in the UK manual not to fill after the pump clicks off but I assumed that this was out of concern for spillage. Day to day we don't do this but on a long run it makes quite a difference.
The point at which the fuel supply cuts off at the pump over here varies from pump to pump so is not exactly a scientific measure. I'm sure the filler neck doesn't hold two gallons of fuel though! There just seems to be so much backwash that the fuel supply cuts off prematurely.

RON is the fuel rating used in most of Europe:
http://en.wikipedia.org/wiki/Octane_rating

Most cars use 95 RON petrol but some higher performance cars prefer 97/98RON. Prodrive say that my Impreza (with the Prodrive Performance Pack) will only give their claimed outputs with 97/98RON fuel but that it is perfectly safe to run with 95RON.

[drbrousters]

I use to think the recommendation was to avoid spillage too. :o Have only known about the other reason for a year or two.

There is a charcoal cannister in the engine compartment (in cars here inthe US) that filters evaporative emissions from the fuel tank (as I understand it). Overfilling can force the fuel itself into these cannisters (expansion due to temperature change). When that happens, it ruins them and renders them useless, followed by repairs or possible engine operation problems. Don't know if its the same in England. Might not even have the system.

If I make a long run, I usually fill it past the first click, but not "to the rim" like I used to. I figure you will burn the gas you overfill before it can expand...especially with the gas mileage :( this "beast" gets...with the speed I drive on trips.

[yottabit]

US gasoline octane ratings are an average of the RON and MON. Supposedly RON represents a well-made, new, modern engine, while the MON represents a poorly-made, old, worn out engine. ;)

In most of the world they use the RON number only. Over here our pumps specifically state on a little sticker "Octane by (R + M) / 2 method)" which represents the average of the "R" RON and "M" MON numbers.

European octane and US octane is equivalent, despite the difference in number representation. Now actual quality of fuel (sulphur, etc.), detergents, ethanol, etc., can be quite different.

Lately everyone puts in the maximum 10% ethanol not just to help emissions, but also because ethanol is much higher octane equivalent than gasoline, so by creating an E10 blend they can use even worse gasoline and still achieve standard octane ratings.

85-octane (US rating) with 10% ethanol?! Stay away from that like the plague. ;)

[drbrousters]

Ninefourteener,
Here in Colorado, reg is always 85 octane. The manual calls for a min of 87. Should we be using the mid-grade 87 and pay 10 cents more per gal?

So here's the answer:
Octane requirement is "sort of" ;) the result of compression ratio. It's more complicated than that, but it's the simple way to put it. The higher the altitude, the lower the compression ratio "sort of";)
. As a result, higher altitudes don't require as high an octane rating (and higher octane at that altitude doesn't increase performance or gas mileage).
Therefore:
The regular and premium octane ratings on your gas pump (at any major oil company station) will be the right ones for that altitude.
The 3.0 liter engine (2006 and 2007 Tribeca) requires premium gasoline (for best performance and to minimize risk of engine damage). The 3.6 liter (2008 and later) performs fine with regular grade.

All this means that regular is fine in Denver at 85 octane :clap: , and premium at 91 (or whatever the octane rating is). If you drive out to the coast, the octane rating for the same grade of fuel will be 87 or higher. It's what you need there.

Doug