Sometimes bad MPG from same gas station

This one ARCO gas station I frequent usually gets me good mileage. I fill up there every 6 days. Occasionally I’ll get noticeably bad MPG on a fill up. The next fill up I’ll get good MPG. There must be a connection there somehow. I doubt it’s a bad batch from the refinery. It must have something to do with the station’s storage tank levels, or…? The difference in my MPG is somewhat astonishing.

 

It's not the gas

 

Thank you oh great Swami!

 

Here's a contact form for the Department of Weights and Measures to file a complaint against your ritual gas station: https://www.nist.gov/about-nist/contact-us

 

To rule out gas being the issue, do a few fill ups at a different station.

But probably not the fuel.

 

Was it hotter out for that 6 days and you ran the a/c more?
Many variables.

 

Just how much difference ? It might be a major difference to you but minor to me.

Is this a company owned station supported by ARCO?

If it is private owned all the Arco Company stations get delivery first. The owner might be buying Gas on the open market. The only issue with storage tanks is water which tends to settle to the bottom.

i trust your measuring via a scan gauge the collects all the data and is pretty accurate .

When you get a poor mileage load of fuel ask the station if the just got a drop . Sometimes this can cause problems stirring the tank up. I never buy gas if the tanker is dropping a load .

All the pumps should be temperature controlled but at times need calibrated again.

looking to how this plays out.

 

I’m sorta doubting my base cab 2003 manual Tacoma is having a monthly PMS or something. I’m not totally ruling out that my 123K engine with no real problem is having an episode. My driving habits are about identical weakly. All the usual maintenance, fuel system cleaners, etc. It’s just…weird how my MPG is pretty OK on two or three fill ups at the same company ARCO and then on the 3rd one my MPG nosedives 25%. One, maybe two fill-ups later the better MPG returns. I’ve ruled out our newly imposed “summer blend” here. The cycle about it got me curious

 

Actually it’s happened again. I got crap MPG the fillup before this recent one. Now it’s much improved this fillup. Due to my recent financial downturn, I’ve been running my tank to almost totally empty before each fillup. Could my 20 year old gas tank have contaminates at the bottom being stirred up? I hear it’s not a good practice to do so. I didn’t wait until empty this time.
Another question if I may. If higher costing gas has detergents and such, why does cheaper discount gas always gets me less MPG (I most always buy detergent gas, even with my current anomaly)?

 

I agree with the peanut gallery; I highly doubt its the gas. MPGs have so many variables that its near impossible to isolate all of them in an outdoor setting.

My MPGs vary from tank to tank dramatically. Last week's tank was at a highly upsetting 16.0 average, with some individual drives dropping as low as 11. This week I'm running in the 20's. No change in weather, weight, habits, route, or speed. ...Or so I thought.

Thinking real hard, the real difference between last week and this one was traffic. Last week had some wrecks on the freeway, it was a lot more stop/go with hard accelerations from 20-60 and back to 20. This week has had a mix of light traffic and heavy traffic, but whichever it was, it was constant - therefore no hard or frequent accelerating. Hence, the difference.


Its going to be something you haven't thought of, and it's going to be a change in driving pattern that you aren't noticing. Theres nothing wrong with the truck, other than its a truck and imperceptible differences translate to huge losses of fuel. There isn't anything wrong with the gas either.

 

Do you have a scan tool? Does the check engine light illuminate in the bulb check part of the starting sequence?

If you have a scan tool I would look initially to see if the engine stays in closed loop after it warms up.

My second thought is do you overfill your fuel tank? After the nozzle clicks off do you add more fuel?

 

Biggest gas robber is the brake pedal.

 

2 weeks in and we still haven't determined what "good" and "bad" mpgs means.. As others have stated, its likely not the fault of this gas station, and there are easy ways to rule this out. Go to another gas station. If you're seeing 25% increase/decrease in mpg between different gas stations, they wouldn't all be in business.

 

What negative effect does doing that have?

 

I wouldn’t have posted if it wasn’t a significant amount, OKAY!

 

There is a charcoal canister that absorbs fuel vapors, if you overfill the tank the charcoal can be saturated in raw fuel, eventually it will be pulled into the motor during the purge cycle… how much will this effect MPG, unkown, it is unregulated. Will the O2 sensors compensate, maybe, depends on if the PCM is in open or closed loop. This is system, everything depends on everything else doing its job from the gas cap to the tail pipe.

 

If it were relating to just your truck, it wouldn't be their gas. Thats kinda the point. And "a significant amount" is completely subjective. Tell us real numbers and you'll get real help. Til then, we're gonna tell you its all in your head.

You got two options:
-its the gas station; switch stations
-its your truck/your driving/other factors; quit blaming the gas station

 

Okay, a drop of 45-50 miles per fillup. There are your freaking numbers, now, take it away with real help.

 

Try another gas station

 

No one addressed my bad habit of being near completely empty before fillups. Regardless, I’ll not be doing that anymore. I’m thinking my 20 year old gas tank being frequently filled when near empty might be stirring up stuff from the bottom. No? Possibly? Or…would my fuel filter be catching that?