Mpg/octane Results

[bajapathy]

Victim/Patient: 1996 SE 4X4 automatic

 

Fuel: Union 76, Cali-craptane...

Driving style: I drive really moderate. Car never saw full throttle, never saw 4000 rpm either. Max highway speed not-to-exceed ~70 mph.

A/C used ~+95%. Same pump at same gas station

 

91 octane, ~40% highway, 60% street: 16.5 MPG. Comments: NONE

89 octane, ~60% Highway, 40% street: 16.5 MPG. Comments: Could be pinging on really steep hills (I live on billy-goat trails in the Santa Monica Mtns), but I think it is a heat shield or something vibrating, no codes

87 octane, ~50% highway, 50% street: 15.3 mpg. Huh. Retarding timing?

 

Even with the drop in mpg, 87 at ~$.10 cheaper pre gallon seems more economical overall than 89.

 

$2.92 x 15.3 = $44.68

$3.02 x 16.5 = $49.83

 

Cheers

Edited August 23, 2007 by bajapathy

[88pathoffroad]

Cool deal, man. Let us know!

[Orangetang]

I keep tabs on my economy with my scanguage. Adjusted for tank error and tire size.

 

02' Chilkoot Editon 3.5 Auto

 

91 City/Highway: 17.1-18.3 mpg

91 Highway only: 18.8-21.4 mpg under 120Km/h

91 Highway only: under 17 mpg over 130Km/h

 

Engine has ~71,000Km on it, drive-train 121,000Km.

 

My last engine ran on 89 all the time and got roughly the same mileage, though I noticed on occasion the spark was retarding slightly, maybe 2-4 degrees. A friend of mine had a 98 3.3L which he ran only 87 in. The first time he pulled a trailer with it the engine started to fall apart after 280Km. Says he traded it in less than an hour later on the 3/4T Cummins Dodge he's been driving since. Maybe related, maybe not.

[XPLORx4]

...scanguage. Adjusted for tank error...

 

Tank error? What's that?

[k9sar]

Tank error? What's that?

 

dents?

[FUELER]

Octane has been proven to have no effect on gas mileage, unless pinging and pre-detonation is brought into the question.

 

I always thought that higher octane, since it is more resistant to pre-detonation, would actually provide less gas mileage, but according to wikipedia, pre-detonation has nothing to do with regular combustion, thus octane has NO effect on gas mileage.

[FUELER]

and heres the text for you:

 

 

Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitues the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics.

 

It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre [citation needed] due to the composition of the fuel as well as increased octane.

 

 

http://en.wikipedia.org/wiki/Octane_rating

Edited August 20, 2007 by FUELER

[bryfry]

I've been keeping close tabs on mine since I purchased it a few months ago. I have since changed all the fluids to synthetic and added Warn hubs. I've adjusted my air pressure to 33 all the way around and just use Mobil or Sunoco 87 octane. I now have achieved 19.03 mpg on the last tank. The last 10 tanks have been both city and highway driving fairly equally. I have seen a steady increase, mostly since the Warn hub install. I started out at around 16.5 mpg. My goal is to hit 20 mpg. I'm using Amsoil lubricants and I'm going to put in their air filter (similar to K & N) next change.

[Orangetang]

Tank error? What's that?

 

The error % between what the scanguage says you burnt vs what you put back into the tank. K-factor, tank error, whatever you want to call it.

[XPLORx4]

The error % between what the scanguage says you burnt vs what you put back into the tank. K-factor, tank error, whatever you want to call it.

 

Ah, I understand now! I always thought of it as a "MPG correction factor".

 

What is yours set for? In my Mazda, I set it to 4.5%, but on the Pathy, it seems to be close enough with 0.0% (no correction). Actually, on the Pathy, I can't seem to get a repeatable FILLUP gallons vs gallons ACTUALLY consumed. Sometimes it reads high by 0.5 gallons, sometimes low. It's probably because I don't fill it up at the same station every time...

[zonianbrat]

I keep tabs on my economy with my scanguage. Adjusted for tank error and tire size.

 

02' Chilkoot Editon 3.5 Auto

 

91 City/Highway: 17.1-18.3 mpg

91 Highway only: 18.8-21.4 mpg under 120Km/h

91 Highway only: under 17 mpg over 130Km/h

 

Engine has ~71,000Km on it, drive-train 121,000Km.

 

My last engine ran on 89 all the time and got roughly the same mileage, though I noticed on occasion the spark was retarding slightly, maybe 2-4 degrees. A friend of mine had a 98 3.3L which he ran only 87 in. The first time he pulled a trailer with it the engine started to fall apart after 280Km. Says he traded it in less than an hour later on the 3/4T Cummins Dodge he's been driving since. Maybe related, maybe not.

 

I gotta ask what... size trailer was your buddy trying to pull? I dont believe you should pull what the manufacture says you can pull. I believe it is like 5000lbs. unless it is around town short distance with no hills. But I pull atv trailers and my boat trailer up in the mountains easily while using 87 octane. These trucks have alot of torque for a little motor but 5000 lbs is just too much and I think your asking to screw up a tranny or something else.

[bajapathy]

Octane has been proven to have no effect on gas mileage, unless pinging and pre-detonation is brought into the question.

 

I always thought that higher octane, since it is more resistant to pre-detonation, would actually provide less gas mileage, but according to wikipedia, pre-detonation has nothing to do with regular combustion, thus octane has NO effect on gas mileage.

 

Theoretically this is a true statement. Practically speaking it is false, given differences in combustion chamber dimensions (size, shape, flame front propagation properties, etc) amongst different engines, and given electronic control over timing and fuel delivery again amongst different engines. YMMV </crappy cliche>

 

The only way to know for sure is testing.

 

 

Cheers

[Orangetang]

I'm no expert but I'd except if an engine is retarding its timing to prevent knocks and pings, there will a drop in performance AND economy. I don't have the pathfinder today but I think the correction is about 5.4% for me. I generally use the same pump to fuel up, but I've noticed that other pumps give different results. Not sure if its pump calibration or the slope of the pad I'm parked on... Probably a mix of both or more.

[mws]

I'm no expert but I'd except if an engine is retarding its timing to prevent knocks and pings, there will a drop in performance AND economy.

 

That is correct.

[mws]

Octane rating has no direct impact on the deflagration (burn) of the air/fuel mixture in the combustion chamber. Other properties of gasoline and engine design account for the manner at which deflagration takes place. In other words, the flame speed of a normally ignited mixture is not directly connected to octane rating. Deflagration is the type of combustion that constitues the normal burn. Detonation is a different type of combustion and this is to be avoided in spark ignited gasoline engines. Octane rating is a measure of detonation resistance, not deflagration characteristics.

 

http://en.wikipedia.org/wiki/Octane_rating

 

I recommend replacing the word "direct" with "significant". Higher octane fuels do burn a bit slower - but the difference is not nearly as significant as the other factors mentioned.

 

So technically, all things being equal, a LOWER octane fuel will produce a tiny bit more power than the higher octane - UNLESS detonation occurs and the ECU retards the timing. At which point everything changes. Dramatically.

 

Bottom line, on modern FI cars with ECU controlled timing and detonation sensors, the experiment bajapathy is performing is a good real world way to determine the optimal grade to use under constant conditions without having some kind of electronic reader/display of ECU outputs.

 

Of course, what is optimal on the highway during winter will be much lower than what you need climbing steep grades at low rpm in the middle of summer....

[Orangetang]

Of course, what is optimal on the highway during winter will be much lower than what you need climbing steep grades at low rpm in the middle of summer....

 

If I rememeber during winter, I'll try to do a comparison. We get about an 80C change in temp between summer and winter here..

[bajapathy]

Bottom line, on modern FI cars with ECU controlled timing and detonation sensors, the experiment bajapathy is performing is a good real world way to determine the optimal grade to use under constant conditions without having some kind of electronic reader/display of ECU outputs.

 

What he said.

 

test test test thats me

 

Of course, what is optimal on the highway during winter will be much lower than what you need climbing steep grades at low rpm in the middle of summer....

 

I figured if it ran ok on 87, the lowest and least expensive grade I could buy, in the heat of summer, and the diff in economy (if any) wasnt significant given the $.20-$.30 per gallon delta, I figured what the fork.

 

And sharing is caring. Except for STDs :tonguefinger:

 

Ciao,

BajaPathy