10 mpg 3.2 - can’t find where the fuel is going

[Showdown]

Karl,

I was out driving today and was keeping an eye on my digital gauge and the MPGs thinking of you.

A few things I noticed:

1.) Any movement in 1st or 2nd gear at any speed and the MPG was low, lower than my total avg. Once I hit 3rd, the MPGs shot way above my avg. Keeping the car in 3rd I could consistently see MPG in the mid 20s around town. In 2nd it was 15ish and 1st was like 7.
Getting the car up to speed consumes a ton of fuel, even for a very light car like mine...

2.) Even with roughly 30 mins of highway driving and MPG in the high 20s, it had minimal effect on the overall average for the 90 minute drive. That is to say that city driving MPG is so low that hwy driving needs to be more time to offset the city...

I also was keeping an eye on my fuel gauge and have determined that like the oil gauge, it's at best, a suggestion.

[mysocal911]

Originally Posted by Showdown

Karl,

I was out driving today and was keeping an eye on my digital gauge and the MPGs thinking of you.

A few things I noticed:

1.) Any movement in 1st or 2nd gear at any speed and the MPG was low, lower than my total avg. Once I hit 3rd, the MPGs shot way above my avg. Keeping the car in 3rd I could consistently see MPG in the mid 20s around town. In 2nd it was 15ish and 1st was like 7.
Getting the car up to speed consumes a ton of fuel, even for a very light car like mine...

2.) Even with roughly 30 mins of highway driving and MPG in the high 20s, it had minimal effect on the overall average for the 90 minute drive. That is to say that city driving MPG is so low that hwy driving needs to be more time to offset the city...

I also was keeping an eye on my fuel gauge and have determined that like the oil gauge, it's at best, a suggestion.

Great, no special cams or chips - totally stock!

[Showdown]

Per my previous comments to Karl, I have M1 cams, EFI and ITBs.

Just providing observations about fuel usage.

[mysocal911]

Originally Posted by Showdown

Per my previous comments to Karl, I have M1 cams, EFI and ITBs.

Just providing observations about fuel usage.

Hardly a good comparison!

[Showdown]

Thanks Dave, your contributions are always insightful, acute and appreciated. /s


Sent from my iPhone using Tapatalk

[mysocal911]

Originally Posted by Showdown

Thanks Dave, your contributions are always insightful, acute and appreciated. /s


Sent from my iPhone using Tapatalk

Since you provided details of your engine & mileage, unlike the OP's, here's mine;

2012 Nissan SUV 4.0L 24 valve 260 HP - city 15 MPG, cruise @ 65 - 25 MPG, mileage - 70K

Meaningless for the OP, right? Now, back to useful info for the OP.

[rwest]

Originally Posted by mysocal911

Since you provided details of your engine & mileage, unlike the OP's, here's mine;

2012 Nissan SUV 4.0L 24 valve 260 HP - city 15 MPG, cruise @ 65 - 25 MPG, mileage - 70K

Meaningless for the OP, right? Now, back to useful info for the OP.

Loren,

Julian’s info is useful in being that he is able to breakdown his MPGs at individual gears which might be useful for the OP in tracking down his poor city mileage.

[ant7]

Bump
There is a valid reason for asking this!
This may help those who are interested in why I asked the question.
https://www.bellperformance.com/blog/bid/117629/octane-and-mileage-does-low-octane-hurt-your-gas-mileage
Ant.

Originally Posted by ant7

What octane fuel are you using ?
Ant.

[Discseven]

Originally Posted by mikedsilva

Maybe you've been driving into headwinds recently???

Mike... city maybe. Not on the highway.

Originally Posted by ant7

What octane fuel are you using ?
Ant.

Ant... "Premium." I know the general rating for this is between 91 and 94 octane. Exactly what for the fuel being run, if this is stated at the pump, I do not know (but will.) Original mpg tests were done using Shell fuel. Thinking it might be a fuel brand issue, switched to Westar. No mpg difference.
.

[Discseven]

Soapbox brake release

This is to compare car’s glide after releasing e-brake to when releasing foot brake. Purpose is to see if either brake system shows any frictional distinction compared to the other. Conclusion = no difference.

Notes:

Done with full fuel tank, engine at op temp, early Sunday morning when no cars were in parking lot. Starting point referenced a white arrow on the pavement to car’s left. Consistently positioned car so that pavement arrow's perspective was always the same as I looked at it each time. Distance from the arrow was consistent but not perfectly measured. Pointing of the car at the start was so it would make it straight through obstacles at left and right ahead. Brakes were released from a dead stop each time. 8 runs were done per brake type. Total: 16.

There’s a gentle downhill that comes to a bottom followed by a slight uphill where the car barely continues.* Past this there’s a very slight downhill and so a subtle increase in speed followed by coming to a very gentle stop.

* Speed is so slow here that I think this location would reveal any subtle difference in the brakes / momentum of the car.

Resulting distances were all within the two black lines seen in the Google Maps image—within roughly 20 foot margin. Distances were mixed among the brake types so neither brake type can be considered dominant. Stopping points were at slightly different angles so the pointing of the car to start with was close but not precise. Given 16 runs, I believe if there was any clear distinction between the brakes, that was given the opportunity to show itself. It didn’t. If nothing else, and assuming the foot brake system is working properly, soapboxing suggests the e-brake rebuild (attended a while back) was appropriately done.

Next, am taking the wheels off for a repeated, more maniacal inspection of each wheel/tire/hub/brake area. May get to this later today.

Sal proposed to check for wheel rotation immediately after releasing the foot brake with the engine at op temp. Focus is on the rears. Premise = might be an expansion of the rubber sections allowing braking but restricting return of the fluid and so there being a drag of either or both the rear brakes. Does fit neatly with poor city mpg and respectable highway mpg.
.

[ant7]

Understood here in the UK we still have 97 octane available at the pumps, and even though I am running a pretty standard engine, there is still a marked difference in performance [and arguably better MPG] from running the 97 octane in comparison to running the standard 95 octane.
Ant.

Originally Posted by Discseven

Ant... "Premium." I know the general rating for this is between 91 and 94 octane. Exactly what for the fuel being run, if this is stated at the pump, I do not know (but will.) Original mpg tests were done using Shell fuel. Thinking it might be a fuel brand issue, switched to Westar. No mpg difference.
.

[PeteKz]

Ant: If the UK rates octane like the EU, then it is about 4-5 points higher than the US method. US method is (R+M)/2. I'm pretty sure the EU method is just the R rating. R=Research octane method; M=Motor octane method.

[ant7]

Pete,
Interesting!
I might have to do a bit of research on that one
Ant.

Originally Posted by PeteKz

Ant: If the UK rates octane like the EU, then it is about 4-5 points higher than the US method. US method is (R+M)/2. I'm pretty sure the EU method is just the R rating. R=Research octane method; M=Motor octane method.

[wazzz]

Ant, yes please, do some research. I'm puzzled too about these figures. Here in France we get only 95 and 98. I have always put 98 in my car. Never used 95. But how does this translate in US figures?
All I know is our 95 is 10% ethanol while the 98 is only 5%.

[proporsche]

Originally Posted by wazzz

Ant, yes please, do some research. I'm puzzled too about these figures. Here in France we get only 95 and 98. I have always put 98 in my car. Never used 95. But how does this translate in US figures?
All I know is our 95 is 10% ethanol while the 98 is only 5%.

In Bohemia we have 100 octane plus i would recommend to get Toluene-3 L(used for racing) per half a tank -It does a magic.It balances the ethanol ...

Ivan

[ant7]

A brief history;

The octane rating of gasoline/petrol was developed in 1927 by Graham Edgar, working for the Ethyl Corporation, makers of Tetra Ethyl Lead (discovered in 1921).

Edgar chose two chemicals for rating the anti-knock ability of gasoline. ISO Octane (2,2,4 trimethyl pentane) had a very high anti knock ability but n-heptane has a very low resistance to knocking/detonation. So we have iso-octane assigned a number of 100, and n-heptane assigned a number of zero. Other fuels are then compared to mixtures of those reference fuels and assigned an octane number based on their detonation resistance. They don't need to contain ANY of those two compounds, they just have to have the same detonation resistance as a given mixture of those two fuels.

Edgar already knew there were fuels with both higher and lower resistance to detonation than those two, but they had the advantage of being reasonable easy to manufacturer and had very similar physical properties so various mixtures would not skew the results when testing against other fuels.

So he already knew that Toluene (methyl benzene), for example had an octane rating higher than 100 (it's about 110), and pure alcohol also has an octane of rating about 109. Neither of those two contain any of the two reference compounds.

And at the other end, some compounds have ratings lower than the Zero of n-heptane. In fact n-octane is rated at MINUS 18 octane.

Yes, one form of octane (iso-octane) has a very high resistance to detonation) and another of the 18 different isomers [physical shapes] of octane has an extremely low resistance to detonation.

At the start of WW2, the standard aviation fuel was 80/87 octane. In 1940, 100/130 octane became available, and in 1943, 115/145 octane became available. that's about the highest commonly available octane gasoline produced. These days 100LL (100 low lead) is the most commonly available aviation gasoline. It's actually 100/130 octane.

The lower number is the lean-burn cruising octane number and the higher number is the full power full rich octane number.

[ant7]

The UK uses the Research Octane Number (RON) system for measuring octane ratings, which is the same system used in most of Europe and the rest of the world. The RON is determined by running the fuel in a test engine at 600 rpm with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Therefore, the UK's octane rating research results using the RON system are indeed the same as those in Europe.

Ant.

[proporsche]

Ant7: when i lived in LA(27 years) i finally found my euro 3,2......it needs 98 and up octane...So after talking couple of dudes they told me go for toluene.These guys used it in theirs bmw M3`s for racing.
All you had to do go to paint shop and get it there-It is used as lacquer thinner.You should see the peeps when i used funnel and pour it into my beast;-))))
So since now i`m in Europe you can get it here in Bohemia but with a permit alias business licence. because unfortunately is used for making pervitin drugs;-(

But my 911 loves it..i mix 100 octane shell gasoline and 2-3 L per half a tank..last time i checked my mileage was par tank cc 650km with some spare fuel...no light of reserve on yet

Ivan

[ant7]

From memory;
Acetone is also known to be used as an octane booster!
Ant.

Originally Posted by proporsche

Ant7: when i lived in LA(27 years) i finally found my euro 3,2......it needs 98 and up octane...So after talking couple of dudes they told me go for toluene.These guys used it in theirs bmw M3`s for racing.
All you had to do go to paint shop and get it there-It is used as lacquer thinner.You should see the peeps when i used funnel and pour it into my beast;-))))
So since now i`m in Europe you can get it here in Bohemia but with a permit alias business licence. because unfortunately is used for making pervitrine drugs;-(

But my 911 loves it..i mix 100 octane shell gasoline and 2-3 L per half a tank..last time i checked my mileage was par tank cc 650km with some spare fuel...no light of reserve on yet

Ivan

[ant7]

And finally, [don't want to continue hijacking the OP's original thread]
This;

https://www.differencebetween.com/difference-between-ron-and-mon/

Ant.