2010 Prius Gas Tank

Another thought, 6.5+35=41.5 litres, not 45 litres as Toyota's spec. stated. I guess you might be able to squeeze in a few more but you're risking gasoline spillage. Obviously that's another safeguard measure implemented by Toyota. Fault them for not telling us, not for implementing the safeguard.

I remember my old Honda Civic stated gas tank volume of 35 litres max. but everytime I fill-up it could only take 32. That translated to 400km/250miles range on 30 mpg average all city driving. We should be VERY SATISFIED with the Prius range of ~600 miles.

Anyway, I've been thinking of not topping up the gas tank everytime. Just fill 13 litres every time giving me about 300km range good for one whole week of driving. That'll lighten up the car for about 22 x 0.7 kg/L density = 15.4 kg = 34 lbs. I don't know if that's gonna help the mpg but I'm trying to time my gas filling day to fall to every Tuesday late evening. Years of experience tells me that's when the gas prices are lowest.

 

This is a key point that emphasizes something about human nature. Our ability to reason is severely limited by our primitive instincts. Whether something is good or bad is determined more by our expectations than by the actual value of the thing.

For example, you go in to get your car repaired. The service writer estimates $400, but after the repair the bill is only for $325. You feel pretty good about it.

Now look at the other case: You go in for the same repair. The service writer estimates $250 for the repair. Part way through he comes back and tells you that they found something else. Now it's going to be $325. You go back to work and tell your friends how you were screwed by the dealership. Same money, different interpretation.

The same thing happens with the Prius gas tank. Some marketing genius decided to list the gross capacity of the tank. I suppose it looks good on the spec sheet, but what it really does is cause false expectations. They should have listed the minimum usable capacity, and perhaps noted that under some exceptional circumstances you may be able to get more into the tank. The tank wouldn't be any bigger, but we wouldn't have these 40 page threads complaining about the last two gallons.

Tom

 

Of all the cars that I have owned the Prius goes the furthest on one tank of fuel. The fact that the tank is small is a wonderful thing!!

I remember my Ford Windstar, 25 gallon tank, i ordered the van with the extra large tank. Ford in their infinite wisdom seemed to use the same tank sensor in the big tank as the small tank. Thus it's additional 5 gallon capacity was while the gauge showed dead empty. I would often run that van nonstop from Tucson AZ to Riverside CA nonstop. The last 100 miles were with the gauge on empty, not a good feeling.

These days the Prius has a bigger "tank" than I do ifyouknowwhatimean:rockon:

 

In NJ the station attendants fill up for us. I took the Prius to Chicago and I've been finding that when I fill the tank there can be anywhere between 2 to 3 gallons between when the gas nozzle automatically stops pumping and how much more gas the tank will hold if you fill it slowly "visually" until full. That can translate into another 150 miles driving range. No one has mentioned this on this thread. Am I doing something wrong filling it up that it should cut off (stop pumping) so soon, with so much unused tank capacity? Are others assuming when they fill up with about 9 gallons of gas that the other 3 gallons were already in the tank when some of the missing gallons are actually AIR because the tank was not completely filled at the "fill up"?

 

I'm surprised you can top it off with an addtional 2-3 gallons after it clicks off?

From everything I've read on this site, when your gas gauge (the last bar) begins to flash, you have about 2 gallons left in the tank. Coincidentally, the computer says I have 5-10 miles remaining until empty. But the computer read-out has been conservatively by Toyota...and you actually have many more miles to go before fully empty.

So, the last time i filled up when my fuel bar was flashing, I put in 9.25 gallons (I let it click off). If the estimate of 2 gallons remaining is close, that brings me up to 11.25 gallons of gas in the tank. Capacity is 11.9 gallons...so maybe i can top off with another 0,5 gallons, but that's about it.

 

I do 4 or 5 clicks and get just about the extra 1/2 gallon you don't with one click.

It does look like most people who carefully fill their tanks when the last bar starts flashing fill it approximately 2 gallons short of the rated 11.9 gallons. Bob Wilson generously went where no man has gone before by running his Gen3 tank dry three times. IIRC, it took a hair over 11.9 gallons to fill each time he did it.

 

Assuming one can put in (about) an additional 0.5 gallons after the pump clicks off...is the rated capacity of 11.9 gallons when the pump clicks off, or, does it assume "topping off".

Not a big deal...just curious.

I can usually put in an additional 0.5 gallons after the pump clicks off. Yes, that usually takes a few clicks to be able to add ~ 0.5 gallons.

 

They wouldn't rate the tank when the pump clicks off, that can vary by
over a gallon from pump to pump.

A logical way to establish fuel tank capacity would be to fill it as full as possible using a normal nozzle on level ground, the run the car until it quits because of lack of fuel. Then tank capacity is how much it takes to refill the tank.

SAE J398 Feb88 has a procedure for establishing a full tank for fuel system tests that require a full tank. The spec doesn't cover rating fuel tank capacity but it does give you an idea how they think about it. The spec says to fill the tank at high flow until it stops automatically, Wait 10 seconds, the fill at lowest automatic rate until it stops, wait 10 more seconds then fill again at lowest automatic rate.

I go 4 or 5 times on the low flow autofill, each time adds less fuel. If you are checking fuel mileage of gas tank capacity, the difficult thing is getting consist results and the fuller you fill the tank, the more consistent the results.

If Bob W is reading, maybe he will tell us how he filled his dry tank and got about 12.0 gallons in

 

Thanks, very interesting.

I always understood that fuel tank capacity was determined by the volume of the fuel tank, and did not include the volume of the filler pipe leading to the fuel tank. Topping off is not part of the rated fuel tank capacity, or in this case, 11.9 gallons.

"The rating is determined by taking an average volume based upon the capacities of multiple tanks. Furthermore, the rated capacity may include only the usable portion of the fuel tank or it may include both the usable and unusable portions. The unusable volume is the portion of the fuel tank's liquid capacity that lies at the bottom of the tank out of reach of the fuel pump. The usable volume is the portion that can be delivered through the filler pipe into the tank when the vehicle is level. The vehicle’s fuel tank capacity does not include the volume of the filler pipe or the vapor headspace, which is the portion of the tank compartment at a level above the filler pipe neck.

Topping off​

Sometimes people attempt to deliver additional fuel after the gas pump automatically shuts off, commonly known as “topping off.” When this happens, the additional fuel begins to fill the vapor headspace and the filler pipe, which are not considered part of the tank’s rated capacity. This may result in a receiving more fuel than the rated capacity in the owner’s manual. This may also occur if the lanes that surround the gas pumps are not level and some of the fuel shifts into the vapor headspace, thus delivering more fuel into the tank."

http://www.oregon.gov/ODA/MSD/docs/pdf/fuel_tank_cap.pdf?ga=t​

This brings into question - When people are calculating their MPGs based on the fillup amount, should we always assume that this amount is equal to the actual gas consumed?? It's the actual amount of gas that's consumed that needs to be used in the calculated MPGs...not (necesssarily) the amount you re-filled. People assume that when you re-fill, the amount you re-fill is equal to the amount consumed. But if the process of re-filling is not consistent, then that assumption could be off. ​

 

Unless the fuel system is defective, you aren't going to fill the vapor headspace in the top of the tank on level ground with a normal gas nozzle.

As far as their comment about the fill tube not counting in the tank capacity, in the real world, you have no way to know if you are partially filling the fill tube with gas or not. I would put more in their statement if the cited a reputable source. I will rate the
SAE more reliable than the Oregon DOT on automotive matters. Oregonians have even been deemed incompetent to fill their own gas tanks :bolt:

You are right on about the need for consistency if you are using tank fills to determine gas mileage.

 

Not even going there.

Capacity is almost always determined from volume. Basic physics, and is a fairly straight foward calculation. Therefore, it seems logical to me that the rated capacity given by a manufacturer, would only include the volume of the fuel tank...since most people do not top off, and to include that volume into the capacity would be very misleading. So, I tend to agree with what the Oregon DOT said - that a car's rated fuel capacity does not include the filler tube.

What I don't know is - of the 11.9 gallons in the fuel tank, what fraction of that is not "accessible" (as mentioned in the article) because it is below, or not accessible to the fuel pump.

 

On the way back from Chicago, I estimated I had enough gas to reach the next service plaza 38 miles away. When I got there the station was closed (they were testing it for leaks). By the time I got to the next gas station, my miles before fill-up was reading 0 . It took 9.5 gallons till the pump clicked off. Topping off I put in an additional 2 gallons. (Total 11.5 gallons).

We stopped off in Pittsburgh Tuesday night. Wednesday, on the way home I had one bar remaining and it said 40 miles before empty. It took 8.4 gallons before it clicked. I topped off with an additional 2 gallons.

The topping off that I'm doing takes about 50 to 100 extra spritzes of gasoline, not 5. It just keeps sucking it up like a sponge. If you were to put in too much too fast it would overflow.

Topped off like this I travel from 150 to 200 miles on the 1st bar (of 10 bars) on the fuel gauge.

So you guys are saying I'm putting 14 gallons in a 12 gallon tank by using the "extra spaces" or am I the only one "really" puting in the 11.9 gallons by filling the above way and the rest of you are only partially filling the tank?

 

Asolof, I have experiences similar to yours. I top off every time, usually adding around 2 gallons beyond the first shutoff. The most I have put in was 12.345 gallons. I normally get > 150 miles before I lose the first bar and once got over 200 miles before losing the first bar.

 

Here's the only thing I'm saying, based on the Oregon DOT article I posted, and what makes the most sense to me - The manufactuer specificed fuel capacity is the fuel capacity on level ground, and is only the fuel capacity for the tank itself. It does not include the filler tube.

My own personal experiences have been, after the fuel nozzle clicks off, I can only add (approx) an additional 0.5 gallons. Often significantly less than that. I think when the nozzle clicks off is a function of: (1) The flow rate into the filler tube and (2) how far down the filler tube you place the nozzel.

 

So Michael, when you fill, you partially insert the nozzle and fill at a slow rate (at least when you are nearing the full point) ?

I've had an occasional pump fail to cut off when doing that, spilling gas.

 

I typically insert the nozzle into the filler tube until the rubber around the nozzle covers the opening. I typically fill up slowly.

 

Well I am a little confused. Is the useable fuel capacity 11.9 us Gal or 10 us gal because of the bladder?

My fuel computer showed 10 miles till empty today, and required 9.5 us Gal to fill. My experience would be to treat the tank as a 10 gal capacity.

I would appreciate more insights.

 

2010+ Priuses have no bladder.

http://priuschat.com/forums/other-cars/94001-gas-gauge-says-full-but-thats-not-quite-true-npr.html might be insightful, even though it's a Ford engineer speaking. Might be better just listen to the <4 minute interview.

 

There is typically about 1.8 gallons left in the tank when 0 miles to empty is indicated.