Fueling problem related to MPG drop?

Had the same problem yesterday...eventually I got 4 gallons in(my tank was 3/5ths' full).

 

Prius runs so cleanly that evaporation of fuel is the largest potential source of hydrocarbon pollution. The fuel bladder reduces fuel evaporation, but this feature does not work correctly if you top off. Topping off also greatly increases the chances of fuel spitting.

Manual per-tank MPG calculations are often inaccurate in Prius because (the bladder, again) you don't know accurately how much fuel is in the tank when you start a fillup; all you know is how much you put in, which is not the same as how much you burned since the last fillup. The MFD MPG calculation in contrast is always very accurate because it uses the amount of gas flowing through the injectors. The only use for manual MPG is to track lifetime MPG, and that is most accurately done using the distance and MPG figures from the MFD.

An MPG decrease in winter is just physics. It takes more fuel to heat cold air, and more fuel to heat up the engine to correct operating temperature. Short trips in cold weather are MPG killers in any car; the Prius display just makes it obvious.

 

nagrath and richard schumacher - Where Are You?

Sure would be helpful if we knew where you are! Sounds like you might be having cold bladder (not yours) problems or altitude issues. Any chance your neighbor is sucking gas out of your tank to piss you off?

PLEASE POST YOUR LOCATION IN YOUR PROFILE

 

I'd rather not say where I am, and there's zero chance that the neighbor is sucking my gas.

It was 12'F here a couple days ago. I suppose the cold makes the fuel bladder stiffer, but, eh, so what. It is what it is and I don't find it a problem, it's just different from other cars.

 

we dont care where you live... but if you want a more informed answer to ANY kind of weather or temperature related issue, you are advisd to post your geographical location or a detailed weather report for the summer when you experienced 50 mpg and for the period you got 35 mpg.

sooo with that, depending on where you are, winter formula gas has 8-14% less gas in a gallon of summer formula gas. therefore, all things being even, your mileage will drop that much no matter what.

the colder weather will keep your car in the less efficient warmup cycle longer. your cars optimum operating temperature is probably around 175-190º...if the ambient temperature is less than that (we HOPE!!!) your car will have to warm up.

your drop percentage is higher than normal only because its not broken in, you are still working on your technique, AND... we all suffered sucky mileage our first year too... sorry... had to add that last part.

BUT

the mileage drop is the same. i averaged 59.7 mpg this summer with 4 tanks over 60 including one at 63.3 mpg. the past 3 tanks, with weather in the low to mid 30's, i am averaging 45-47 mpg. so you see, my drop is about the same as yours.

couple things... have you gotten any kind of gauge for your Prius? i have the SCANVIEW and it has given me some data that emphasizes the temperature thing.

after less than a month, i can easily see that only in extreme circumstances would i need to worry about overheating. i have a PriusChat colleague who lives in the same town as me who has a block heater (reduced that warmup cycle i told you about) and a radiator blanket.

now in most cars, it would be a bad idea to cover the radiator. of course, most cars are much more inefficienct. The Prius wastes so little power, that even small things like defrost and heat, will affect mileage which are things we take for granted in a normal car which is better at heating its surroundings that it is at moving you down the road .

also with SCANVIEW, i have noticed that even on trips of 20 minutes or more, my Prius never makes it to optimum operating temps at street level speeds. (35 mpg or lower) unless im driving aggresively or doing a lot of elevation changes. the reason... i average ICE temperature drops of 5-7º at traffic lights. (the gauge will actually drop as much as 10-15º but that is because the engine shuts down and the water stops circulating... something a regular car does not have the benefit of) i tracked my ICE temps at 30 second intervals on 3 separate trip that i posted in my blog. max temps on 15 minute drives with minimal stops was 167º. the longest trip i did was at 35º and it took 18 minutes to get over 170º (only briefly however because had stop light and temps went back down to the low 160's) and had to speed up to 40 mpg for 3 minutes for it to get that high.

as far as the fillup problems. i recommend that you take that nozzle and shove into the tank as far as it will go. that is the way its designed to be used. also after the shutoff. there is no reason to be looking down the filler hole...its not like you can see anything anyway. i have a description of how a gas pump shutoff works. reading that will illustrate that improper techniques will cause premature shutoffs. its important that no air escapes from around the nozzle while you are filling the tank. that is why a tight seal is necessary.

try this, fill up tank with a nozzle that has a good rubber seal. if the seal is trashed or missing, go to another pump or another station. hold the nozzle as tightly as you can to the tank compressing the seal at least a few inches. fill till it stops. without reducing pressure (no need to strain. i just take a firm hold and lean on it a bit...it is time-consuming and boring i know) go ahead and clunk in more gas to your desired fill level. i can nearly guarantee you that this method will result in no spilliage of gas.

 

Nagrath,
That's not normal behavior. Talk to your dealer. Some Prii are a little finicky about fueling but not like that. Sometimes I have a little trouble getting the last gallon in, but not the first.

 

hmmm umm. remember i said if the seal is damaged or missing go to another station

remember... i advise you try this. its up to you. you know what results you are getting by the method you are using now... i think you need to try my suggestion at least twice before you tell me what doesnt work.

and the comment about location was directed at the post stating that they didnt want their location posted

AND

on the winter formula thing. in my state, ethanol is a year round thang. that does not contribute to the lower gas mileage figures. summer formula gasoline freezes at 40 something degrees. components that lower the freezing point are added in winter time and they DO NOT burn, but take up space hence the lower mileage figures.

 

well its only a suggestion. if those types of pumps are not available, you will have to try something else. a tight seal is beneficial to the filling process

 

Whoa! Winter gas differs from summer gas in having a greater fraction of volatile organic compounds (VOCs), often butane (according to Wikipedia). Those DO BURN. Here's an article that describes the difference between summer and winter gas blends: http://www.slate.com/id/2098672.

Summer gas does not freeze anywhere near 40 degrees F! Did you mean -40 (which is the same in F or C degrees)? Or 40 Kelvin? Since it's a blend, it doesn't have a specific freezing point but does get more viscous with lower temperature.

The more volatile components that are removed from summer gas have more energy per mass than less volatile components, but less energy per volume because they are less dense. So a winter blend does have a little less energy per volume at a given temperature, but since it's sold and used at colder temperatures it may actually have more energy per volume (since it's density is greater at lower temperature).

 

Ditto that. Nagrath (for my next stupid question) have you tried filling at something less than the maximum flow rate setting on the nozzle? Do you have the same problem at multiple gas stations (not merely at different pumps at the same station)?

 

well i can only give my thoughts on the situation. in my blog entitled gas pump shutoffs there is an excellent description of how gas pumps work.

there is basically a y shaped tube when a valve that allows gas to flow. attached to it is a check valve that prevents backflow and is at the end of a tube that creates the small hole in the end of the nozzle. in that small tube is a diaphram that controls the check valve. when it senses pressure it closes the check valve and the pump shuts off.

its my theory that the bladder causes pressure variations from gas sloshing back and forth in partially full state. this creates a rush of back pressure that will flow out only if allowed too or if the seal is not tight and allows air to escape out. normally the Bernoulil principle creates a vacuum of air that sucks back to the check valve and leaves it open. so it acts as a bleeder valve... not enough bleed off to suck out liquid, but enough that no large amount of pressure builds up...

besides, i tried the fill halfway...let the tank settle and continue and that was a disaster. soon as i stopped, couldnt get started again. i fill to the first stop then usally add to the nearest buck. from my SCANVIEW, my tanks either are 95 or 97% full (only have had two fillups since getting ti...) and when i fill, i make sure that the pump is in as far as it will go. the pump is on an island that is half a step up. so i stand on the island, get a good grip on the pump handle, and lean back with all my weight onto the car when i fill. i have only once spilled gas and that was the 2nd fillup on my car when i was doing what you did... barely putting the pump in...what can i say? just doesnt work for me. and besides, the reason for those gaskets is to reduce air polution when refilling. unburned gasoline is waay more toxic

 

Sometimes getting a fill started is a problem. Starting slow then gradually increasing flow helps.

If you do top off, be sure to fill no more than .2 gallons at a time, then pull out the nozzle between times. I call this burping the baby. If you don't burp your baby, it will spit up.

 

This is one of the things that worries me, whenever everyone is talking about how many clicks to pump at, i keep scratching my head. I live in Upstate NY. or Really upstate for you nagrath. The pumps have no seals, no clicks. We're lucky if we get a rubber flap at the handle. We have no auto fill. I guess i could fuel slowly with a light squeeze, but that will get old quick. I guess i'll have to test after i get the car.