Why do I average the same distance after every pump? Does the MPG display really matter?

Can someone either explain how it hurts the evap or link the thread that explains it? I have searched and all I keep finding is references that there is a thread. I topped off on my Saturn for over 200,000 miles before getting this car and never had a problem. As a car guy I'm confused as to how this could harm it, but then I don't that much about they hybrid system yet. Any help would be wonderful.

 

I'm a second-click filler myself, it's usually a very miniscule amount.

 

But, this does nothing to improve your mileage. And very little to improve calculation accuracy, especially beyond a single tankful. It does increase the possibility of spillage or fouling something, tick off the folks waiting on the pump, and um...: that's about it, LOL.

 

If you did the same method every time, your accuracy would actually be better because you don't have to know if the pump is mis-calibrated or not. As for the spillage, yeah, that is always a concern, you just have to pay attention. It's still a 9 gallon tank and every car around me is going to be waiting longer than me even when I'm filling to the brim. My Saturn was 12.2 gallons and even when filling it to the brim I'd get out of there quicker than every other car at the pumps. Still curious if someone can send me the link as I tried again and couldn't find it. I don't mind being wrong, really just curious. I'm starting to wonder if one person said this and everyone believed him, now that it's been that way for 10 years it's law. I can understand the point to not do this on the gen 2's with the bladder, but I've personally never had a problem. But as I mentioned before, I don't know that much about the Prius drive-train yet, so please help me out here.

 

UH, please reread my original "if no one is waiting behind me". It most certainly improves 'manual calculation' as every pump I go to has a different 'shut-off' sensitivity i.e. full at one pump, is no where near at another, is somewhere in between, is etc...... Not sure about the on board calculator.
That said, you do have to be aware of premature egasculation.

 

I found an ap for my Iphone that I am now using to calculate. It is called MPG for Free. Quick and simple to calculate. Stick 2 numbers in and done.
Would never hold anyone up at the pump. That gets under my skin. When local, I fill up in the evenings, as there are fewer folks needing fuel. If on a trip, and the line is long, I get what I can, as fast as I can, and hit the interstate.
Good discussion.
Dan

 

Well, my wife filled up during the week, and had her first encounter with a pump that asked in advance how much $'s she was likely to be needed. Just a new hassle, the options are maybe 30/50/100. Something like that. Anyway, the trick is to just say the maximum. I didn't know, neither did she. So anyway:

She took a stab, said $30. Then of course, the pump shut off when it $30. And she was stuck with a half-filled tank, and drove off.

When I entered that into my spreadsheet, it tells me we got insanely good mileage on that tank. I put a comment beside that value that it was a partial fillup.

Next tank, the calc is will insanely bad mileage. It all averages out.

I see on Fuelly, you have the option to tick an entry as being a "partial fillup". I did that, and it doesn't add that entry to my chart. I assume nstead it waits on the next entry, lumps them together.

 

Interesting. The station I use just puts a $100 hold on your card. Which seems like a lot for many people...

 

Another family member has a Pilot. $100 often isn't enough.

Yeah, the various reg's foisted on you at gas stations can wear thin. Like on Oahu for example, if you have an out-of-country (or even out of state?) card you can't pump gas, without leaving your card with the attendant. No such restriction on Maui though.

 

All I can say is that I've grown up with a lifetime of official advice that says don't do it, for all sorts of reasons. All Australian governments (state and federal) and the state motoring organisations say not to do it, to avoid fuel spillage from overflow valves while driving or going around corners and many also talk about increased emissions (example).

Generally Gen III Priuschat threads (like this one) suggest the reasons not to do it on a Gen III Prius are the same ones as for other cars generally.

The car's owners manual also says it quite bluntly. In the 2012 model manual it's on Page 108 and quite simply says:

Fortunately given our fuel "price cycles" down here this is rarely something I ever think about (I buy fuel when it is cheapest - if it will take more than $5 worth on the day I predict to be cheapest of the cycle, then I will stop in and fill the tank (to the first click) so I can last through to the next cycle minimum)... but for those of you who do top-up or indeed those who strive to drive the car until it almost-but-not-quite runs out of fuel, what is the perceived advantage of doing so? I've never really understood it.

 

I appreciate the reply. I missed this on my first pass-through of the owners manual, looking back my Saturn had that as well. Guess I got lucky? I do like having pertinent information to the vehicle, but I don't listen to the old adages anymore. Change your oil every 3k, give the car 5 minutes of start up time every time no matter the weather, check and adjust your valves every other oil change... some of these things die out with technology.

 

It will minisculely decrease MPG, since that gallon increases car weight.

 

Roughly 6 pounds per gallon... I sure wish that the C would have had a 12 gallon tank like my Saturn did, although I can still go farther which is nice.

 

There are a couple reasons I 'top off';

1. There is typically a .10 difference between PA and NY gas prices in my area. I live and buy my gas in PA, but do most of my driving in NY. I want to be able to get back to PA without filling north of the border. Sometimes the difference is even greater, as a couple local stations have gas sales on designated days.

2. I drive about 1,100 miles per week (often over 200 miles, and sometimes 300 on any given day).

 

Hi everyone! New poster here. I just got my Prius C two weeks ago and I love it.

I wanted to chime in here because I somehow have driven almost a thousand miles on it already (that's what I get for going to a dealership and hour and a half away I guess). I have done way too much highway driving on it already, but I'm definitely not getting the low mileage the OP is talking about.

I have filled up twice so far, the first time was 8.44 gallons after 412 miles, the second time was 8.43 gallons after 396 miles. That comes to 48.82 mpg and 46.98 mpg. Granted that's not all highway driving, but I'd say at least 2/3 was.

I'm definitely using gas with ethanol so the OP's issues can't be because of that. I did inflate my tires to 42/40, I'm not sure what the OPs are at. I know mine came from the dealership at 25(!).

 

Welcome to PriusChat

With the pressures you found on your regular tires, it would be worthwhile to check the pressure of your spare. The usual pressure for the spare is 60 psi, it's embossed on the tire iteself. You'll probably need to drag it out to get at the valve. Maybe let them know what you find.

 

This mini-article over at Car Talk explains pretty succinctly why overfilling your fuel tank is unwise. In short, you can ruin the fuel vapor reclamation system.

 

Thank you for posting actual evidence... I was starting to think it was just old-timey fud brought about from the gas crisis so that you wouldn't put as much in the tank.

 

My pleasure!