"Letting your gas tank get below 1/3 full will cost you MPG"-Myth?

[dchurchwell]

I've read that letting the gas tank get below 1/3 full can cause you to lose MPG when you go around turns. Supposedly your gas will not go to the engine if it is being slung to the side? I do not know much about cars, am relatively new to hypermiling, and deliver pizzas (lots of hard 90 degree turns at highest possible speed). Thoughts?

[SKurj]

electric fuel pumps..

[dchurchwell]

are you saying this is a myth? like i stated, i don't now much about cars, and certainly not what an electric fuel pump does

[Altitude]

Never heard that one before. But the premise is all wrong. If gas is getting slung up to the side and is not making it to the pump, then you're actually using no gas, which is good for MPG. Worst that could happen is that you get an air bubble in the fuel lines which might make the car hiccup.

Of course if you are driving in circles at high speed and the fuel is permanently slung to the side of the tank, that's a different story altogether.

[STC]

Hmmm? Never heard that? I always thought letting your tank go well under 1/8 all the time 'could' cause your fuel pump to go early? The fuel pump is inside the gas tank...

Cheers! :smile:

[SKurj]

Hmmm? Never heard that? I always thought letting your tank go well under 1/8 all the time 'could' cause your fuel pump to go early? The fuel pump is inside the gas tank...

Cheers! :smile:

Yes now that one i have heard, let the tank run real low and the pump is no longer submerged therefor getting hot... but i dunno if the yaris has an in tank pump or not..

[sickpuppy1]

And also, with the temp changes this time of year, you are much more prone to getting condensation in the tank. The more air (with moisture trapped in it) in the tank is subject to cold-hot changes make it more prone to picking up moisture in the tank.

[thebarber]

ive only heard that letting your tank run lower than 1/4 tank consistently over the life of the car will cause premature fuel pump wear.....im going to play it on the safe side, personally.

[dobbiedoo]

The tank has baffles built in, so there is never a chance of gas not being around the pump. As mentioned before the pump can overheat with a really low level of gas, shortening it life.

[malibuguy]

our cars have pulse fired fuel pumps...i'm not worried about it

hell, most of my "fun corners" are when i'm doing some EOC (engine off coasting)

[R2D2]

Malibuguy,

Can you describe a pulse fired FP for me? I haven't heard the the term before and I'm unfamiliar.

What are the advantages?

Thanks in advance,

R2

[malibuguy]

for at least toyotas small cars (in terms of the years i'm referring to)

'97 & later Tercel, Echo, Yaris feature returnless fuel systems to reduce the heat thats introduced into the fuel being pumped up to the rail (soaking up heat there from the engine bay) then back to the tank. Going to returnless reduces evaporative emissions which is also aids in mileage. The fuel pumps are pulse fired to maintain rail pressure, since they can't be run all the time.

does that make sense? let me know...i'm kinda of crappy at explaining things

[R2D2]

Nope, makes perfect sense, thank you! I never thought about the returnless aspect of the fuel system needing a different type pump. I see what you're saying.

These seem to be reliable units-at least I haven't heard of any problems?

My last vehicle my Dad aand I got really good at dropping the tank, if you know what I mean!

Thank you,

R2

[malibuguy]

my tercel chassis has about 210-215k on it, still original fuel pump...but i did have to replace the tank cuz it rotted out from being a NE car

all cars by now are returnless

[JumpmanYaris]

This was on Mythbusters and it was busted.
If you don't know what I am talking about (proven wrong)

[daf62757]

Wouldn't the tank with less volume actually be lighter and get better mileage from less weight?

[rick996]

Wouldn't the tank with less volume actually be lighter and get better mileage from less weight?

Yes

[Idahotom]

I wait as long as possible to fillup. Partly because hauling less dead weight around is always a good thing, and partly because when I calculate my mileage after the fillup I want the biggest numbers possible for the most accurate determination of how I did that tank.

Just because the fuel pump is normally submerged, does not mean running low levels of fuel are harmfull, I gotta think they take guys like me into account when they design the things! I don't worry about my fuel pump in other words.