Is it worth reducing the cars weight by 45 pounds... by...

I keep at least 1/4 tank in my Energi since I typically only need gas for a trip to a neighboring town which that will easily cover. I don't think it makes a meaningful difference in EV range.

 

Wish I had a short enough trip to make this possible. I would just end up sitting in those annoyingly long lines at Costco more than once every 5 weeks (yeah I know I'm spoiled - I hate waiting in gas lines )

I assume that this is a viable enough option for those who charge at least 1x per day with a relatively short drive.

 

Peanuts, I wouldn't even think about it. But then, I'm packing around a lot of extra stuff, including a close to 20 lb jump pack lol.

 

I only filled the gen2 tank up about half way, but that was because I believed the head pressure and pressure from the expanded bladder when fuel could pushed more fuel through the pump.

An old rule of thumb, which may or may not apply to hybrids and EVs, is that reducing a hundred pounds would improve efficiency by 1%. Not filling up all the way could improve efficiency, but I suspect you won't notice it until looking over an entire year. In a PHEV, I'd consider doing it more so that there is room in the tank to add fresh gas if the fuel maintenance warning coming on was a concern.

 

nah.

 

Being a plug-in is a factor tho, can see that.

 

in the pip, they recommended burning through a tank every 6 months. in prime, there seems to be no such recommendation.
and not only that, the pip runs the engine every 124 miles, if it hasn't run. in prime, there seems to be no such exercise.
so, i can only think of 3 possibilities:
1) gasoline is far superior now in longevity than in 2012.
2) primes engine isn't bothered by stale gas.
3) i lost my train of thought.

 

I wonder of water contamination would be an issue if we were to never fill completely up with gas? I’m also concerned with the freshness of gas as well. I could see us going a very long time on one tank of gas, as in months and months. I wonder if regular use of STA-BIL is necessity...

 

Prime manual re fuel:

 

A 45 pound weight reduction would improve mileage by around 0.8%.

 

no bladder since 2009. not sure about moisture.

i would think heeding the o/m instructions posted by @joachimz would be sufficient.

 

Ethanol bonds to water good.

 

Like GM, Toyota was being conservative in regards to fuel condition in their first PHEV's tank. GM went with premium octane requirement, and Toyota more frequent fuel burn offs.
Once they got the real world data in, they saw the precautions needn't be as cautious.

These tanks are sealed tight to reduce emissions, and to keep the fuel fresh. They are a far cry from a tank used to fill your mower. I'd only worry about water in humid environments, then adding rubbing alcohol will be enough to keep off phase separation.

I'd leave the tank partially empty not because of freshness concerns, but so I could delay a mandatory ICE running by adding some fresh gas.

 

Yes, but too much water will cause the alcohol and water mix to separate from the gas, and sink to the bottom of the tank. Not good.

E30 and higher concentrations, and phase separation is no longer a concern.

Edit: I was up against a forced restart clock before. So to add to this, ethanol is hygroscopic, and will suck moisture out of the air. That's the reason I would give thought about water contamination in warm, humid environments and PHEVs. When gas is used, some of that moisture laden air enters the tank. So more water can get into the fuel.

How much this is a concern is going to depend on quickly you use the gas.

Is the Prius tank plastic? This might no longer be an issue, like 3000 mile oil changes, but I've heard that keeping the tank under filled risked rusting of the upper part of the tank.

 

In regard to fuel freshness. Modern fuel has come a long way. I have two very recent examples:

Case 1: My wife's friend moved to an apartment complex that allowed only one car and had assigned parking. She needed a place to keep her PT Cruiser (2nd car) until she purchased her own place. We kept her car at our house. This turned into a 2.5 year storage. It didn't move. I washed it once. She wanted to come pick it up this week, so I checked it out to make sure it was ready. Put a new battery in it. It had an oil change about a month before storage, so I just checked it and topped it off. Checked air pressure in the tires and topped off. Turned the ignition key and the puppy fired right up after about 3 seconds of cranking. Took it for a drive around the neighborhood, no problems, but I also never exceeded 35mph. Stayed in the neighborhood because plates expired in late 2015.

Case 2: My wife's father passed away 2 years ago. We inherited his 1995 Chevy K1500 pickup that has only 100,512 miles. That truck has been sitting on our property for 2 years. It also never moved. We decided it was time to get it back on the road and retire my 280,000 mile 1994 F150. Put air in the tires, installed another new battery. It took three tries before it fired up, but runs smooth as can be. Unfortunately, both front brakes and the driver side rear brake were seized from sitting so long. Powered through them to get the truck to the garage and rebuilt/repaired all the brakes. The truck runs great. Still haven't added any fresh gas to it.

I wouldn't worry too much about the gas getting old.

 

You could always do a test. Pick a route, longer the better. Run it with 1/4 th tank, record your results and then do the exact same route again with a full tank. Your results will be more meaningful if the wind is the same on both runs. Wind will have a bigger effect than the weight.

I can tell you when I did my 805.2 miles on one tank experiment in my 2010, I did over several runs. I also noticed the incremental mileage I got during each intermediate run. I saw no significant difference in MPG from the gas tank getting lighter. What I did see, was impact due to wind.