Living Dangerously: The Fuel Light

Here's a thought for folks who want to shoot for a "furthest on a tank of gas" record: Why not run a "reasonable" tank of gas through the car and then do a simple extrapolation to determine how far one would have gone using the full listed capacity of the tank (taken from the manual) assuming the same average MPG? Then no worries about running dry. Assuming running dry is not part of the appeal of these attempts?

 

Fuel gage below half, my gas station brand coming up, I pull in. Five minutes later, with a full tank, I'm on my way. Like pakitt, I use very little of the info screens, mainly the Hybrid Synergy Indicator, Trip A with accumulating fuel economy (just for feedback, know it's bogus), and the odometer, for calculation. The rest of it, the new "ECO score", miles to empty, all that jazz, I don't care for.

 

Well, I will probably care about it at the beginning, first couple of months. Then I will probably don't look at it anymore once I get a feeling for things.
There are a few features of the new screens that seem useful and appealing, as it was with gen3.
In the end now in the Gen3 I have only the HUD set to show me the speed and the 1 mins/5 min fuel consumption to show me what I am doing and for statistics at the end of the trip. (I am writing down all my fuel consumption per commute since 2011).
Everything else I don't really look at it anymore. (Not the there is much more to see in the gen3 )

 

I do to find out:

• What are the actual out of gas indicators in car?
• The as built tank volume versus lying specs?
• From warning to actual out of gas amount remaining?

Because I am still curious and alive.

Bob Wilson

 

I want to have some realistic idea how much fuel range I can actually get out of a car. Specific incidents and enormous gauge uncertainties have been described in older threads. I don't expect understanding from folks who didn't experience the OPEC Oil Embargo in the U.S., don't remember fuel rationing systems where drivers could not legally buy fuel on certain days, or who have never seen roadside signs such as these:

gas150km.jpg by fuzzy1 posted Oct 14, 2012 at 7:01 PM

DSCN1334gas106c.jpg by fuzzy1 posted Mar 22, 2014 at 10:15 AM

gas163mi2.jpg by fuzzy1 posted Mar 13, 2014 at 9:27 PM

Where you live, with essentially no fuel price competition or gouging, you can use that strategy at no cost. With no significant opportunity for commodity price arbitrage, careful fuel price planning gains nothing. Despite our close proximity, the pricing pattern on my side of the border is very different.

Based on some actual experience, I have little confidence that the lower reaches of the tank, beyond what I've previously used, are really truely available for backup or emergency need.

 

Lots of uncertainty and speculation about running out of gas in this thread. With over 75 tanks on my GenIII, which holds 11.5 gallons, I almost always go right to the _0_ point. And it seems to take ~9.6 to 10 gallons to where the handle sensor shuts it off. That means I have more than a gallon left - every single time. Enough margin for me to trust the _0_. Mind you, I won't do that out in the desert, or across stretches of Montana that I don't have first hand knowledge of. But I do trust what the gauge tells me based on the history of the car.

If you fill it when it is somewhere half full, or put x numbers of gallons in it to make it an even $10 or something, you'll never really know to trust the estimate. Embrace the 0 miles left, if you dare. Or make it 50, whatever you are comfortable with. But note how many gallons you are filling with - write it down in a log-book, and I'll bet you will begin to trust the miles left indicator more with every fill up.

 

Trust but verify

 

I understand completely - Odd or Even days, anyone? As far as the "Next Gas - XXX Miles", I'd top it off now and enjoy the scenery...

 

@fuzzy1: You deleted the first sentence of my post. What I actually said was:
"Here's a thought for folks who want to shoot for a "furthest on a tank of gas" record: Why not run a "reasonable" tank of gas through the car and then do a simple extrapolation to determine how far one would have gone using the full listed capacity of the tank (taken from the manual) assuming the same average MPG? Then no worries about running dry. Assuming running dry is not part of the appeal of these attempts?"

This applies only to people seeking a "record" and suggests changing the way the "record" is defined. Instead of actually trying to go as far as possible and risking running dry, why not simply extrapolate to the distance one would have gone assuming one could use the full tank volume spec'd in the manual? Change it to a sort of virtual contest eliminating the hazards.

Perhaps I should have been more explicit. I was referring to this thread (and other similar ones):
800 mile per tank challenge | PriusChat

That's all.

 

Several times I measured my Gen-3 tank at 12.1 gallons total and the gas remaining after 'flash' of 2.1 gallons.

Bob Wilson

 

I'm confused. What does the last part mean?

 

Our 2010 Prius has 2.1 gallons remaining when 'flash' begins. So I reset "B" trip meter and calculate how much I've burned by dividing miles by MPG. I typically don't fill until I'm down to one gallon so I'm usually adding 11-11.5 gallons.

Bob Wilson

 

You guys are nuts. I've never seen the fuel light in my 2004.

For one thing, I generally fill up when I'm at Costco, and I go there more often for food than I would need to just for gas.

For another thing, in the winter, I don't like to have less than 250 miles of range and in the summer, not less than 150. I've been stranded before on a highway due to an accident (several times).

One time, I was coming home from skiing and a jack-knifed semi had to be towed up I-70 the wrong way. They had us all doing U-turns on the highway and driving the wrong way to get out of the way, resulting in an extremely long diversion - instead of 50 miles to go, it was 167 miles to go, in the winter, in the mountains, with a ton of traffic on roads that can't handle that much traffic. 4 hours instead of 45 minutes.

90% of the time I fill up with half a tank or more. The other 10% are always above 2 (of 10) bars on the fuel gauge. And I have driven over 550 miles on a tank before.

 

I've never run our of gas with my 2007, 2012, or the 2016, however, I ran out of gas with my 2001 and was able to drive about 2 miles on the electric motor to a filling station. I find it odd that the Prius will not allow you to go over about 20 mph with the EV mode set, but (at least with the 2001) it would go 50 mph on just the battery when it was forced to.

 

I'm in the same mindset. Maybe a Costco thing, lol. The coffee bean and rolled oats bags may be running low, but out in the garage on shelves: the next ones are at the ready, and the case of tomato sauce, and...

 

It is trading off risk for overhead:

• Driving around town, my threshold is 1 gallon remaining because I know where the 24 hour gas stations are located. Actually, I wait for Costco to open and get cheap gas.
  
• Going out of town, I top off before reaching the Interstate, ideally three miles away where gas is still cheap. I also address biological issues.
  
• If it is after sunset in a strange area, I keep it high enough to reach the next town or Interstate truck stop . . . flash is good enough knowing I have about 120 miles left.
• Testing the tank, I put a 1 gal spare can in the car when down to 1 gallon and avoid construction zones or areas with no shoulders.

Bob Wilson

 

That would make sense in a Tesla where the range is poor and the time to refuel is long. In a Prius, the range is long and refilling takes 3 minutes so the overhead is almost nothing. Not worth any risk, IMHO.

 

From experience, I am quite reluctant to trust certain things that I haven't personally tried at least once before for verification. Fuel gauges and claimed fuel capacities are among those things.

The first tankful of my first car ran dry with the fuel gauge still reading above 'E'. A later car's fuel gauge dropped to 1/2 much too rapidly, and had a third of its useful fuel range below 'E'. Without that range, I would have been paying several extra dollars at each (unnecessarily early) refill along the way on one of my regular trips.

I started doing this back when driving that first car with a fuel range less than a Tesla. It ended saving actual $$. Having a Prius is no reason to quit.

The specific incident involved a weekend where most fuel stations closed for a major holiday, in a region and era generally lacking 24/7/365 service, when memories of the 1970's Energy Crises / fuel shortages were still clear. A plan change left me leaving one town without a full tank, so I intended to top off at the next place on the route with fuel, 50 miles away. Though it still had over a half tank, that was not known to be enough for the next stretch in that short-range car.

Due to the holiday, all but one of the usual stations were closed. The one left took advantage of the 'opportunity' by tacking on a mandatory 'pump unlock fee' equivalent to a half a tank. And the clerk made very clear that the other customer and I could not split that fee. We both walked out, and I sweated the 130 miles to the next known all-hours fuel. (Since then, service availability has improved, and the DOT has put up signs marking refueling detour options.)

After that, I started characterizing realistic fuel ranges of my cars, and identifying the best prices along the way. Since mobile internet arrived, fuel preplanning now saves several dollars per tank on average. In one extreme case last year, knowing realistic range on the family ski trip vehicle (not the Prius) saved $1.70 per gallon as we exited California.

This potential savings varies by region. When traveling in Mendel's province, prices are so uniform that the money saved amounts to only a couple Canadian dimes per tank. But within my own U.S. zip code, prices typically vary $0.80/gallon within walking distance.

 

In the Houston area the gasoline prices don't vary by that much. The highest prices are generally near our airports (about 30 cents more per gallon). You know, to gig the people that have to fill up their rental cars before returning them. However, there is one Shell station that is consistently at least 30 cents per gallon higher, and it is located right at the NASA entrance. (Maybe, they consider NASA to be an airport.)

 

I have seen this many times when traveling.

But curiously, at this moment, most of the stations on the approach to SeaTac Airport's car rental return are charging less than the area average. Except for a single station, the only one at a particular I-5 exit, charging 45-60 cents more than those closer to the airport.

Today's spread is 54 cents in my home zip code, 64 cents in the next door zip code that is the primary shopping district. This is a narrower spread than normal over the past few years, likely related to the current low fuel prices and the flat price trend of the past month.

When skiing in British Columbia, I've seen prices exactly the same everywhere in town, top-name and no-name alike, and adjacent towns being only 1 or 2 cents different. Safeway would be 5 cents lower with a store receipt coupon code, but the undiscounted price on the reader board was no different than everywhere else. It was a big deal when the Costco in Kamloops was 5 cents under everyone else. Here, that uniformity would be taken as prima facie evidence of illegal price fixing.