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I've noticed that I get much better mpg right after I fill up. I've noticed as much as a 15 to 20 mpg increase over 2 week old fuel for a very similar set of driving conditions. Has anyone else noticed this?
 

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Oh please, like 2 week old fuel is old. More likely your driving conditions change or your eyesight. Fuel at the pumps is older (before they get a new shipment), than you will most likely see in your Insight.
 

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scutterbob said:
I've noticed that I get much better mpg right after I fill up. I've noticed as much as a 15 to 20 mpg increase over 2 week old fuel for a very similar set of driving conditions. Has anyone else noticed this?
You are on to something here Bob. I've seen the effect and it has been noted in other Insight forums over the last few years.

Age of the fuel is a bit of a stretch, but its temperature seems possible. There is both a summer cooling and winter heating effect.
Or maybe neither.

A control to the hypothesis would be to "pull-in" to the station with say 1/2 tank. Stop for the near equivalent time a normal fill-up would take, reset one MPG counter and continue the normal route home. You probably should repeat the routine several times and try to normalize weather and temperature The data would then show if there's a difference in this scenairo vs. really adding fuel.

How about proving or disproving your observations for the group?

HTH! :)
 

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I noticed a 15% increase in fuel efficiency compared to my normal daily drive home after filling up with "warmer" fuel.
Knowing that the engine is more efficient when it's warm the temperature of the fuel should make a diffirence in winter.
 

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I had the same exact experience.

I have not had the same experience when I fill up with half a tank or more - it's only when I'm almost out and I fill up with fresh fuel that I get vastly superior mileage. I really think it has to do with 2 main things: the engine is warmed up (it's about ~15 minutes to the fill station from work on the way home) and the new fuel is held underground at much higher temperatures than my current fuel in my tank.
 

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I have considered this for over 2 years. There is a psychological effect: right after filling the tank, we often have a tendency to try harder; to watch the mpg graph more, and save fuel. You see in our subconscience, we want to get this new "tank of gas" off to a good start, and we drive more carefully. Billy...
 

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Billy said:
I have considered this for over 2 years. There is a psychological effect:

<snip>

Yup, there's gotta be a psychological factor.

That's where the data can't "lie". But there *is* something going on. On more than one ocassion I've seen the lean burn window open w i d e with the mid summer cooling effect. I even "tested" what I thought I was seeing by pressing harder on the gas pedal to feel this "expanded" lean burn window. It was there! Else my psychological factor expanded to the delusional state <VBG>.

So Scutterbob, can call you Bob? Are you game?
 

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Resist said:
Well I think I can say you've got the "new" record for the most concise reply, ONE word. <VBG>

And I now have to try and interpret this reply to mean the data has been collected and confirmed as "psychological"?

And since (following this same train of logic) it follows that I am delusional, what's the Bingo prize? <VBG> (the data would be nice or a link to the thread)
 

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Discussion Starter #10
I don't think the psychological effect is happening, because I really tried to kill my mileage when I filled up to test this observation, and I was really babying it on my way to the station. I want to get a ODBII that I can hook to a computer and record data for a while (any recommendations?). And some form of portable weather station cause it also seems I get a rather wide range of mileage based on weather changes. Btw, yeah Bob is fine. I'm not sure if there's much temperature difference between whats in my tank and whats in the stations tanks. I live in central FL, our ground water temp is between 69 and 72, and our air temps currently average around 65. But I have also now begun to wonder if its a deep mostly pure tank, vs the crud in the bottom kinda thing.
 

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From what I have noticed, I think the fuel temperature is the key.


I purchased the software (downloadable) and cable from
http://www.obd-2.com for $122 including shipping.
I ordered it Saturday and recieved it Monday. Tech support is great. I emailed them witha question about GPS yesterday and received a reply yesterday. I am going to order a laptop GPS module that will be linked to the the OBD software. It already has a GPS button.
 

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I think in my case the "psychological factor" kicks in at the end of a tank.

I use Trip A to track the miles and MPG for each tank. I reset it with each fill-up and then go back to the LMPG/Odometer display.

Each leg of my commute is ~35 miles and I can only fill-up at the beginning or the end. As I near the end of a tank, I'll switch to Trip A to note the miles when (or if) the Low Fuel Indicator lamp comes on. This is so I can record it in my Excel spreadsheet with all the other data (we ALL do that, right? :lol: ).

As a result, I end up watching the MPG display and trying harder to keep it from falling (if I'm on the uphill leg) or keep it high (downhill!). I know someone is going to say "Why not just do this for the whole tank?". My reply, "Who do think I am, 'Insane Wayne'!" (sorry xcel, 8) )

Anyone else have the "end-of-tank" factor?
 

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scutterbob said:
<snip>

Btw, yeah Bob is fine. I'm not sure if there's much temperature difference between whats in my tank and whats in the stations tanks. I live in central FL, our ground water temp is between 69 and 72, and our air temps currently average around 65. But I have also now begun to wonder if its a deep mostly pure tank, vs the crud in the bottom kinda thing.
Ok, Thanks Bob! :)

Your air and ground temps seem to kill the temperature theory. AFAIK the "fresh" fuel theory is even farther fetched. Gravity simply isn't a strong enough force to separate the lighter fractions of a hydrocarbon liquid mixture. And I'd bet your stations tanks are filled much more frequently then you might think. Plus the pumps intake is somewhere near the bottom of the tank, else you'd never be able to empty it.

As you can see its easier to disprove a seemingly plausible theory than prove it.

A scan tool that can also access freeze frame data is more desirable than a simple code puller. If you've already got a Palm or Pocket PC then software and cables are available. I use Auterra for the Palm, http://www.auterraweb.com/ there are lower cost plain code pullers available that won't access the generic OBDII data stream so google for your choice.

Weather station "data" sounds like a bit of overkill. With a scan tool you can access the IAT (Intake Air Temperature) sensor on cold start to determine your "local" temperature. And its the only one that matters as far as the Insights computer is concerned. <g>

HTH! :)
 

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Looks like this thread lost the definitive(?) reply from xcel. Evaporative emissions purging allowing additional fuel in therefore reducing the "metered" amount of fuel and making the lean burn window HUGE. Well, in a lean burn window sort of way. <g>

And for the record xcel's observations limited this "super" lean burn window to around 3 miles.

Makes sense anyway. I _knew_ I had felt and tested this on more than one occasion. It is much more than psychological. There is one specific moderate hill on the last lap home. I can _never_ maintain lean burn up this slope except with this rare after fill-up behavior. The station is about 5 miles from the house with the hill about mid way.

So without some bother to repeatedly bypass the evap purge hose on fill-up and observe if this eliminates the effective MPG boost we'll never know for sure. My experience has been somewhat "random" in that the amount of increase is not always the same nor directly related to weather. Which is consistent with a variable amount of fuel vapors recovered by the evap system. A "scientific" study will need to be done over months with the evap system both normal and temporarily bypassed (for a short time after fill-up ONLY).


HTH! :)
 

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Anyone out there with a real burning desire to know this, and some real dough, could buy a fuel totalizer like what's used in aircraft, and once that's installed, it'd be easy to track the fuel usage.
Let us know what you find out. - Berk
 
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Hi All:

___I don’t know where the first one went but here is a repost of my observations:

___After a regular fill with fuel filling parts of your Insight’s Vapor recovery system, this excess fuel is sent back to be consumed and it will not be recorded by the FCD as fuel coming from the Fuel Pump. This is the main reason some might see 100 + mpg’s heading out of the gas station for a few miles or higher then normal FE after a fill. Whenever I fill a long tank, I have experienced this effect for anywhere from ½ - 2 miles before she settles out. A regular long tank for me is > 11.1 from fumes or the rarity when I can fill her with up to 14.1 + gallons. Again, usually from fumes.

___Hopefully this helps explain some of what the membership is seeing in their own Insight’s.

___SeanW, in my best James Cagney impersonation: “You dirty rat …” :D

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:ejhzc1mp][email protected][/email:ejhzc1mp]
 

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fuel

After a regular fill with fuel filling parts of your Insight’s Vapor recovery system, this excess fuel is sent back to be consumed and it will not be recorded by the FCD as fuel coming from the Fuel Pump. This is the main reason some might see 100 + mpg’s heading out of the gas station for a few miles or higher then normal FE after a fill.
This is what I always assumed any fuel increase was. But I haven't really noticed it more than on one occassion.

Of course, I've only filled the car five times since purchasing it in late August.

I do think Mouse likes Supra from Chevron best. :wink:
 

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I wonder if it has anything to do with the weight of the car? Ten gallons of gas is around 60 pounds. This would be bad for short trips with lots of starts and stops, but migh be good on the highway.

Easy enough to test by adding 60 pounds of ballast.
 
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