Fillup Question

Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection
Topping Off the Tank? You Might Want to Think Twice

 

What's the point? Why do you have to be different? Just fill up until the pump clicks then go back when your tank is empty or is at a point you feel like refilling.

 

I think if a person wants to know the exact MPG this would be the method.

 

curiosity killed the cat.

 

and ignorance is bliss... until it isn't.

 

For the particular tank, that's possible. However, over, say, five or more tanks (even assuming different click-off levels for different pumps, which may not be a legitimate assumption), if you're planning on continuously monitoring actual mpg, you're basically going to get the same level of accuracy in your calculated mpg anyway just letting it click off.

 

yes you can do it, should you? no.. you will eventually cause evap. system problems.

 

Has this been confirmed or is it an urban legend? I see no posts anywhere on Priuschat about people having to replace their evap system.

 

This only works if you use the exact same pump nozzle... whereas filling till you see fluid works everytime. I'm not advocating one way or the other, just saying it's more accurate.

 

Yes, you can do it. But you're going to lose some spilling out and by evaporation. It's wasteful and bad for the environment. You shouldn't do it.

One guy claims he fills up 2 more gallons by topping off on another thread. That means he saves one less trip to get gas every five tanks. See if you can make that argument. How much more gas are you getting in there?

 

How sloppy are you at filling your tank that you spill all over the place? ... that's besides the point. I don't think there is any way he is getting 2 gallons.

 

I'm the only that drips gas after a fill-up? Am I the only one that drops meatballs or ice cream on my shirt? Grrrr...
Two gallons is what the guy claims. It's unlikely but if that's true, he has a good argument for topping off.

 

I made it up to scare you. In fact you should top off you can drive further..

If you ever seen a fuel evaporator system, you would quickly understand why...

I'm sure it's on PC somewhere or just search.. even if it's not in PC doesen't make it ok. A quick search, I already found this. Titled just for you..
Debunking Fuel Myths

Debunking Fuel Myths - Cars.com

 

You're right... media never regurgitates things. I know the manual says it, I get that. I am not doing it, which is why I say that I don't advocate it or advocate against it. I'm just wondering if this is speculation. I did this on my 2001 Saturn for over 12 years and never... I repeat... never had an issue with over 200k miles, but guess what. The owners manual in the Saturn said the same thing.

I did do a search on Priuschat... I would imagine that if someone had to change their evap system, this would come to light really quickly... but thanks for jumping down my throat for asking a question.

 

If you want to achieve an accurate reading on your mpg by filling up to the top and then driving until nearly empty and again filling up to the top of the tank will give you a 100% accurate reading.

This is how Wayne Gerdes of Cleanmpg.com conducts his reviews of several vehicle he has driven for his mpg results. As far as I know the vehicles that he has filled to the brim have had no ill effects.

I know for a fact on the 2010 Prius when you fill up on the slow speed after the first auto click off you can still pump
in another 2 gallons of gas until you near the brim of the tank. I have only done this a few times and our Prius has have no ill effects, no warning lights or poor engine performance or the smell of gasoline in the passenger, driver area.

Also in the 2010 Prius owners manual there is no warning mentioned about filling up the gas tank to the brim that I could find in reading the manual.

 

It's in the "C" manual. I have read it. Seems crazy that you can add 2 gallons of gas, that's a lot of wasted space.

 

Fuel Evap. system designs are all different. Just because you didn't have an issue doesn't mean it's ok. Read up on it if you doubt it.. if you don't care, so be it. Newer systems are monitored. older ones are not.

You can also see it this way, do you think that car makers go through all this trouble to design a fuel evaporator system to scare you? lol.. also, what's the gain here? oh right.. 2 gallons of gas.

 

More on the urban myth! written just to perpetuate it..

OBD-II Trouble Code: P0440 Evaporative Emission Control System Malfunction

 

No, it works regardless of pump nozzle over the course of a number of tanks because with, with a tank of finite space, you decrease the amount of error with each successive tank.

Think about it this way- you go 400 miles and then put in 8 gallons of fuel. If you fill up to the rim (as you did last time), you can be pretty sure of the accuracy on that particular tank. However, if you just let it click off (as you did last time), no, you don't know exactly whether the gas you put in was just replacing the gas you burned going the 400 miles, or you put in more, or less- for that tank.

However, if you let it click off over 5 tanks, on the fifth tank you've just finished replacing five tanks' worth of burned gas with that last click. There will, again, be some error for the particular 5th tank, but now all of the errors have been correcting for each other over the past four tanks. For example, your last fillup led to an early click-off so that you didn't put in as much gas as you had burned going the distance you recorded. However, because not as much gas got in, you had to get gas just a little bit sooner, and you couldn't go as far.

In other words, over the course of five tanks (or ten tanks, or 15), the 1 or 2 or 6 fluid oz. error not of how much gas you put in, which is quite accurate (and what you're using to calculate mpg), but of how much room is left in the tank (and thus how much you burned to go the distance recorded), becomes smaller and smaller with each successive tank vs. the 8 gals, now 16 gals, now 48 gals, etc. Over time, you end up with the same accuracy.