V8 gas mileage with mods......horrible

GX4SEVEND

GX4SEVEND

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So I am currently in Anaheim for my daughter's competition. We drove here in the gx470. Little over 700 miles. Granted it's lofted, all wheel drive, 35's, v8........I get it, I didn't buy it for gas mileage. However, on the drive here, once I got gas in California the first time, I'm getting 165 miles to the tank. On board computer is showing 9mpg. And the math shows about the same. Only thing I did was switch to a full synthetic oil.

Within the last 5k I've done.....tranny flush, new radiator, all new diff fluid and the oil change. It's at 96k now.

Any ideas? I was getting 220 a tank in town before this trip
 
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What is your hand calculations telling you? 9mpg is pretty bad even with a headwind to be honest. I'm running 33" E-Load LT Tires, a SW Bumper, OLW lift, and RCI full steel skids front to back; I'm seeing usually in the low teens for "bad" mileage on the freeway.
 
So as soon as you got into CA your gas mileage became shitty? What kind of gas stations are you going to? Are they Chevron's, Shell or Circle K's and 7-Eleven type places? 9 mpg is terrible man. Cali also has some hilly areas, lots of winding roads around mountains, lots of traffic….all will affect your gm.


Have you checked your calipers?
Air pressure in your tires?
 
That is pretty low. I drive from Portland to San Francisco and back once a month and generally see 18-19 mpg at 65-70 mph on my stock 2006 Limited V8. Are you carrying a heavy load and/or have any thing on your roof such as a luggage carrier?

FWIW, I have tried using 91 octane (premium) gas and it makes no difference in mileage over 87 octane (regular).
 
Range said:
So as soon as you got into CA your gas mileage became shitty? What kind of gas stations are you going to? Are they Chevron's, Shell or Circle K's and 7-Eleven type places? 9 mpg is terrible man. Cali also has some hilly areas, lots of winding roads around mountains, lots of traffic….all will affect your gm.


Have you checked your calipers?
Air pressure in your tires?
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I've used chevron, shell and a Pilot station. All on 91 premium. I also had tires balanced and rotated prior to the trip. Running 38 or 40 psi I can't remember.

Before I left, I filled up at Fred Meyer has station. Had 30 cents off a gallon so why not. Went from southern oregon to Redding before I filled up and was at 170 or so miles and still had a quarter tank. Now in California at 170 miles the light is on. I'm stumped.
 
Well the MPG getting worse in CA vs. Oregon doesn't surprise me. Ran into this myself a couple times when going to Bend.

California like to force E10 on everyone regardless if they want it or not; it doesn't improve mpg unfortunately. The fuel I picked up in Oregon actually got me a bit better mpgs because it didn't have ethanol in it. But 9mpg is still bad.
 
Hopefully it is just the quality of gas here. We have 10% ethanol in oregon too. It's just a dramatic drop in mpg
 
What was your average cruise speed?

On my wussy 2WD V6, my highway mileage will go from about 21-23 mpg at ~55-60 mph, down to about 20-21 mpg at 65-70 mph, and 75-85 mph it's down in the 18-19 mpg range (and yes, not far from me there are lots of highways with posted 75 mph signs, and some with 85 mph signs).

I can imagine a V8 with all that stuff causing probably 50-80% more aero drag would be pretty horrible at high speed.
 
Gas here in SC is $1.77 a gallon. Ethanol free runs about $2.99. 9 miles a gallon is still 18 wheeler or Humvee low.
 
BlackWorksInc said:
Well the MPG getting worse in CA vs. Oregon doesn't surprise me. Ran into this myself a couple times when going to Bend.

California like to force E10 on everyone regardless if they want it or not; it doesn't improve mpg unfortunately. The fuel I picked up in Oregon actually got me a bit better mpgs because it didn't have ethanol in it. But 9mpg is still bad.
Click to expand...

This is the issue. Ethanol has far less power than regular gasoline. It is just a filler.
 
Ethanol won't make that big of a hit to mileage. You're looking at about 3-4% reduction in MPG going from E0 to E10.

It's only about 25-30% when going from E10 to E85.


To the OP, 9 mpg is pretty bad at that speed. I was thinking you'd say you were booking it at 85-90 mph, which would still be bad, but somewhat understandable given your Cd is likely in the 0.5-0.6 range, and you have more frontal area than stock.

My first guess would be front O2 sensors if they haven't been replaced. I suspect mine are aging a bit, as my mpg has gone from a ~22-23 mpg combined now to about 19.5-21 mpg with the same driving. When they get old they tend to get slower to respond, so they won't trip a CEL, but they'll generally cause you a bit of mileage. After that, maybe slight vacuum leaks or something?
 
Winter gas gets lots of butane as well. Cheap filler, and adds some volatility for those super cold days. Not used in summer because it evaporates fast and makes for bad air.

As to gasoline (RBOB) itself, it's all the same except for a pint of the trademarked magic stuff they dump in when the tank truck fills up. Ever notice how rare it is these days to see a branded gasoline tanker ?

Sorta like beer being beechwood aged. They drop a small chunk of wood in the billion gallon tank of beer...

It is true that some pipeline transmix (up to 5%) may get mixed into regular gas (diesel, kero jet fuel) - premium gas is protected from this very minor contamination.
 
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I just wasn't aware of the differences between states and the quality of gas. I've always ran premium and oregon has 92 at every station. Here In California it's 91. Didn't think a 1 point drop was a big deal but mixed with all the other points people have brought up maybe that's enough to drop it 5mpg

I agree about the fuel trucks though. I see the same company delivering to all the stations here in town. I had my economics professor say that exact thing almost 15 years ago.
 
GX4SEVEND said:
I just wasn't aware of the differences between states and the quality of gas. I've always ran premium and oregon has 92 at every station. Here In California it's 91. Didn't think a 1 point drop was a big deal but mixed with all the other points people have brought up maybe that's enough to drop it 5mpg

I agree about the fuel trucks though. I see the same company delivering to all the stations here in town. I had my economics professor say that exact thing almost 15 years ago.
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run 87.
unless it specifically calls for 91, you are just wasting money.

also, running too high octane on an engine that doesn't require it, could theoretically give you worse mileage.
 
Octane, State Blends etc

I would go with the 02s...it is just about the only logical theory...If you had a brake dragging that hard I think you could see/smell it once you stopped the car and got out.

Take a sniff, and see if it smells rich..or just wait for the CEL to trip..either way dont neglect eventually it will clog the converter
 
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