Filling up with the good stuff
 

As I was topping of my tank with high test gas today I realized I'm getting screwed. If the guy before me used the low grade then everything left in the hose is low grade and I'm leaving high grade for the next guy. Anyone have any idea how much gas is "in the hose"? If I'm only putting a couple of gallons in I'm really screwing myself.

Many years ago in engineering school I had a fuels and lubes class with a lab. We used a knock engine to determine RON (Research Octane Number) of various hydrocarbons including gasoline straight from the pump and various gasoline brands and octane ratings blended together. The result was generally the RON in any brand was understated at the pump, and blending various grades and brands occasionally resulted in an octane higher than the highest grade in the blend. The professor (a retired API wonk) speculated that different types of octane boosters in each brand were present in slight excess to guarantee the stated octane rating, so mixing the brands allowed the excess booster to raise the octane on the other brands by using a different chemistry to boost octane. No idea if it's true, but I've never had a problem mixing brands and grades due to this experience.

The gas in the hose is irrelevant if you just plan and prepare your gas budget for a full tank, this also saves you time as you fuel less often. I suppose just a gallon or two might affect the octane rating but I doubt it, depending on hose length there is probably no more than a quart of gas in the hose. I wont get into the acceptable water content found in gasoline, knowing that might make you blow a gasket... JK I honestly think you are being concerned over nothing. The key is do you run additives? Things like Chevron with Techron helps counteract the effects of Ethanol. Several other vendors use additives, Chevron is just one example.

Simple solution: go to a gas station that has a different hose for each octane grade of gas. We have one like that where I live that sells only ethanol-free gas. Best of both worlds ;)!

Get your gas, including the gas in the hose that the other guy paid for. Then shut off the hose but keep the nozzle in your tank and wiggle it around and get the last bit of your gas too. Free gas! The next guy can suck it!

* I actually have no idea if that works or not ;)

I just give it a good chug from the hose and spit out like a fine Bordeaux. 89 has a tart finish but good body. 87 is like a cheap pino grigio from the Olive Garden. It's hell on the chompers but I'm not about to start pouring money down the drain!

I hate nothing more then stations that have an ethanol free pump, but it only runs 87. Leaving higher grade fuels full of ethanol.

That's what we have here where I get my 94 octane. :cheers:

Really?? If it's due to financial constraints that you're only putting a couple of gallons in, you're definitely driving the wrong car! :eek:

According to various sources (google is your friend), it's less than 1/3 gallon in almost all cases. This is regulated state by state, so check with your state's Dept of Weights and Measures. They are the people who inspect and certify gas station equipment to make sure the consumer is getting what they pay for.

If you are filling up your tank, it has around a 17 gallons of capacity. 1/3 gallon of the wrong octane rating is going to be so diluted into the right stuff as to be a complete non-issue. It would make up less than 5% of your full tank of gas.

Even if you are only putting in 3 gallons (and why the hell does anyone do that?) remember its still going to be diluted into the same approximately 17 gallons as well. Assuming that what you had in the tank already was the right stuff.

If you are cruising around on "E" then buying 3 gallons, then back to E, then 3 gallons, and on and on, then yes, you are going to have a higher percentage of "bad gas". But if this is what you're doing, you don't need a Boxster, you need a Honda Civic.

really, the only people who should even care about this are motorcycle riders who have a motorcycle that needs 93. My bike does, and I have a 3.8 gallon tank, so that 1/3 gallon is a bigger deal to me. But honestly, I've never had a fuel related issue with the bike, so I'm not worried about it at all.

^ I never run with more than half a tank. I've convinced myself that less weight over the life of the car is easier on the consumables. And now you tell me I'm losing a dollar!!!

Putting a couple gallons into the car over and over is silly - but there is something to be said about keeping the tank on the lower end (well, not full anyways). Gas can add a lot of weight to the car. I know people who swear by only keeping the tank half full and they see a 'big' improvement in their MPGs. They also feel the car performs better (it's lighter). Plus they say it keeps the gas fresher, especially in a car that sits for extended periods.

Not sure how accurate it is, but the belief is out there.

WTF ????

half a tank to save weight for better MPG? You must be joking!!!
Gas weight just over 6lbs per gallon so 8 gallons is approx 48 lbs

I know for racing, they watch every pound, buy that is to squeeze out every ounce of performance and sometimes has to do with rules as well.

As far as effecting MPG, sure, it will have some effect, but probably measures in 10ths at best. If you are so worried about weight, did you take out your spare and toolkit? Running lightweight wheels? No extra crap in the car?

Big improvement in MPG, no way!!
Big improvement in performance? get driving instruction, its unlikely you drive anywhere near the top of the performance envelope in your Boxster. 50 lbs ain't gonna make a difference

Having just dug in there, at 1/2 tank on the needle the top of the fuel pump is just beginning to be exposed from under gas.

No rear cats or spare.

The boxster is the only car I've driven that feels completely different on empty and full. You feel the weight in the steering really easily.

Oh my... the mere thought of this discussion has me feeling the 986 forum just crossed over into BMWCCA / Bimmerfest territory...

Sad sad day :(

Many years ago I had a book called Drive It Forever (based off an earlier book called More Miles Per Gallon). Both were written in the mid-70s during the gas crisis when there was some cause to fret over the smallest details. Of course pumps were very different, but I believe the book mentioned that the fuel trapped in the hose was a little over a cup.
Either way I've lost very little sleep over it. ;)

Near me there is a Mobil that had a pump that would run on after you stopped it. Not full force, more of a steady dribble. Enough so that if I didn't top off and went inside for a coffee and left the nozzle in the tank it would continue slowly filling my tank for free. I learned this the hard way after stopping the pump short of full so I could check my oil and washer fluid one day...

That would be your opinion. Frankly, lots of members are commenting, and I think the topic of full tank vs. part tank is a bit interesting, albeit totally unscientific.

Some people think it makes a difference, others think it's just silly. Facts and figures vs. how something feels - can lead to some fun debates!

I usually keep my car full simply because I can't be bothered making the extra trips to the pumps, but I am intrigued by Jake's comment that he can feel the difference. Now I want to get out and burn some gas off to see if I can too.

:dance:

Butt Dyno
Perception becomes reality