Sta-Bil and fuel economy

[NeroM]

All summer my partner has been getting slightly over 130 mpg from her PCX150, primarily commuting on rural roads - including dirt/gravel. Her normal speed is around 40 mph.
Depending upon fill up location put in either non-ethanol gas or a high detergent premium Egas.
The PCX does seem to have a preference for non-ethanol, this fuel is approx 10-15% heavier than Egas.
Last week filled up, Egas premium and added an ounce of Sta-Bil treatment, as depending upon the weather- she may not consume this fuel before winter storage.
Suddenly, a drop in mpg to around 117-120 mpg.
Trying to figure out the reason for this drop ?
Road surfaces are the same.
Weather, especially in the morning is getting cooler, sometimes in the upper 40s. Perhaps a little more aerodynamic drag? Also, considering a "bad" batch of gas- what ever that might mean. Perhaps they put regular in the premium tank. We got around 120 mpg on a tank of regular Egas.
The only real difference is the stabilizer addition.
Has anyone experienced a drop in fuel efficiency from adding Sta-Bil ?
Thoughts ?
Thanks !

[Mel46]

I would not expect a drop in fuel economy. However, the objective of adding a fuel stabilizer is to keep the fuel from separating. At the same time, if there is any water in the fuel the stabilizer will encapsulate it so that the water will be expelled/used instead of settling in the tank. This may be what you are seeing.

[GeorgeSK]

I definitely see a drop in fuel economy when it gets cold. I'm not sure that the Sta-bil has a detrimental effect (a half ounce doses the '13 PCX tank - hard to believe it could have THAT significant an effect), but one never knows. You can see on my fuelly history that I get my best mileage in the dead of summer, and that tank that goes through the winter is comparatively abysmal.

Mantis Milage.jpg (113.12 KiB) Viewed 1010 times

I no longer commute to work or ride the PCX on a regular basis, so fillups are much fewer and farther between than before. That too is probably not good for my mileage. I now put Sta-bil in every tank -- there is no knowing how long it will be there. As an aside, I can only get 10% ethanol gasoline in my state unless I go to an airport. Ethanol gas has less energy content than "pure" gas, so it figures that mileage will be down when you use it.

[Inoplanetyanin]

The drop you report is pretty meaningless as your real range compared to the long term averages is too high of a ratio.

In other words, your results are not statistically significant... Stabil has nothing to do with fuel economy in the setting you described, neither would a difference in gas be detectable. Wind on the other hand, can determine whether you will be seeing 150 mpg or 60 mpg within a single trip, so would the fluctuating level of gas used depending on when the pump auto shuts off.


If you feel I am missing the point, then describe precisely and in details as to which methods you used to determine the mpg you mention in the first post, and don't forget to mention the mileage over which the measurements are taken and calculated.

[vito]

I use Stabil once a year for both my scooter and my motorcycle. Have done so for decades, and every Spring the bikes start up instantly and run fine, other than a lot of exhaust smoke until the Stabil is burned up (I guess). And maybe its me, but getting the kind of mpg the PCX gets (for me it seems to be about 95 to 100) a small percentage drop, if it occurs, is of no consequence at all. I compare the PCX mpg to my Honda Goldwing that gets 38 on a good day and I just smile at this great little scooter.

[jburner]

I definitely see a drop in fuel economy when it gets cold. I'm not sure that the Sta-bil has a detrimental effect (a half ounce doses the '13 PCX tank - hard to believe it could have THAT significant an effect), but one never knows. You can see on my fuelly history that I get my best mileage in the dead of summer, and that tank that goes through the winter is comparatively abysmal.

Mantis Milage.jpg

I no longer commute to work or ride the PCX on a regular basis, so fillups are much fewer and farther between than before. That too is probably not good for my mileage. I now put Sta-bil in every tank -- there is no knowing how long it will be there. As an aside, I can only get 10% ethanol gasoline in my state unless I go to an airport. Ethanol gas has less energy content than "pure" gas, so it figures that mileage will be down when you use it.

I wonder how much of this can be attributed to winter blend fuel. I do know that along with cold weather (at least in my state), winter blend fuel give me a noticeable difference in fuel economy.

Taken from this website... https://www.goldeagle.com/tips-tools/wh ... mer-fuels/

"The other reason for the higher cost of summer-blend gasoline is that refineries have to briefly shut down to transition from winter to summer blends. This typically occurs starting in April, allowing gas stations to start selling the summer blend by May or June. They can then switch back in September."

This fits almost exactly with the readings on your Fuelly mileage report.