"Empty" fuel warning: results of an experiment

[ericst]

Because of the uncertainty that seems to ensue whenever any of us gets a flashing "E" bar on our fuel gauges (how much gas do I have left at this point? how much further can I drive?), I decided to conduct a little experiment.

I decided to note the odometer reading at the exact time the "E" bar started flashing on my vehicle, and then to drive the Prius until it ran out of fuel, following the odometer reading & MPG gauge along the way. And because of the well-known dangers of driving the vehicle without fuel, I made sure that I was ready for when the inevitable would occur--with a 2-gallon gasoline container in the back.

RESULTS:

From the time the flashing "E" bar and the "Add Fuel" message first appeared on my Prius, I was able to drive exactly 102 miles, with a computer-displayed tank MPG rating of 37. After the 102 miles, the inevitable happened, with the large red triangular exclamation point and all kinds of other amber warning indicators on the dash indicating that I was out of fuel. I could indeed continue to drive the vehicle at this point, but only at slow speed, using the battery. Because I was prepared with my gasoline container in the back, I only ran the vehicle for approximately 30 seconds in this out-of-fuel condition (basically the time it took me to safely navigate to the side of the street and park & shut down). Interesting to note that during the out-of-fuel time period, battery level was going down quickly--lost about 2 bars (from 60% to 40%) in less than a minute.

Environmental conditions: Chicago city driving, a lot of shorter trips, relatively cold weather with temps generally in the 40s (some down into the 30s, some up in the 50s). This, by the way, accounted for my fairly "low" 37 MPG (which is still more than double what my previous Chevy Prizm was getting in the same conditions). Vehicle has ~ 1K miles on it; tires have been kept at 38/36 front/rear psi. Actual MPG on my car has generally been 2-3 below computer-displayed values.

And for those of you who are wondering about the ever-popular "tank capacity" question, I was able to fill up with 11.4 gallons (including what I poured in from the gas can) after running out of fuel, using the semi-aggressive fill-up methods detailed elsewhere on this site.

INTERPRETATION & SUGGESTIONS:

1. When "E" flashing bar appears, tank is approximately 1/4 full (has about 2.8 - 2.9 gallons left in it; consider 2.5 gallons to be on the safe side). This seems to compare favorably with what john1701a and others have written on this site.

2. How to plan your tank fill-ups: May I suggest the following?
- When "E" flashing bar appears, immediately reset the Trip B odometer (so that you don't have to remember how far you've driven since that point).
- Follow the Trip B odometer, in conjunction with your computer-displayed tank MPG rating.
- Miles driven on Trip B & suggestions:
Zero: Ok, whatever...
1.0X tank MPG: Need fuel soon...
1.5X tank MPG: Time to have a specific refueling plan!
2.0X tank MPG: You SERIOUSLY need to work on getting fuel!
2.5X tank MPG: IMPENDING DOOM...
2.8X tank MPG: dead Prius
In the future, based on my "experiment" above, I'm probably going to plan on refueling at 1.5X tank MPG after flashing "E" warning to be on the safe side. Others have suggested 50 miles past flashing "E", which is near this range. Never again will I plan on running out of fuel--the dangers are obvious.

3. It might have been nice if Toyota had designed its fuel indicator to read flashing "E" at 1/8 tank instead of 1/4 tank, but now that we know, I guess it doesn't matter as much. Perhaps they'll develop some kind of "fix" in the future.

4. There may be variations between vehicles, relative to remaining fuel capacity at flashing "E". Your vehicle may behave differently, so be conservative! (At least one other post on this site has reported running out of gas at 1.3X MPG miles past flashing "E"... I can't reconcile that with my experience.)

5. This post is NOT intended to speak to the question of overall tank capacity, the "bladder" problem, fill-up issues, and related fuel gauge issues. I'll leave that for others to dissect.

6. This post is NOT intended to encourage others to run out of fuel, either intentionally or otherwise. As others have correctly stated, this is a dangerous practice and can seriously damage your vehicle. I was worried doing this even for 30 seconds with a can of gas ready in the back!

I'd welcome others' comments, feedback, criticism & correction on this. Hopefully, it will be helpful to everyone.

[Danny]

Eric, what an extremely helpful experiment!

If you don't mind, would you mind copying and pasting your experiement into the Knowledge Base so that we can be sure to have it for future reference?

Perhaps others with the same cojones you had can replicate the experiment in other climates and conditions to see what their outcome is, as well.

[paulisme]

Wow, very informative! Thanks for sharing

[ericst]

Originally posted by AdminCoop
Eric, what an extremely helpful experiment!

If you don't mind, would you mind copying and pasting your experiement into the Knowledge Base so that we can be sure to have it for future reference?

Perhaps others with the same cojones you had can replicate the experiment in other climates and conditions to see what their outcome is, as well.

Done!

[earthlovergrrl]

Eric....thanks soooo much...I had no idea you could go that far after the flashing bar comes on, that's great! I've been filling up within 10-20 miles after it comes on, doh!


Les

[ericst]

Originally posted by earthlovergrrl
Eric....thanks soooo much...I had no idea you could go that far after the flashing bar comes on, that's great!  I've been filling up within 10-20 miles after it comes on, doh!    


Les

Ok, but still be careful. Like I said in the post, I'm still concerned that there may be variability between vehicles (and between different environmental conditions) with regard to this. Until you feel comfortable with your own vehicle's performance, if you decide to go even beyond 1X MPG past "E", you'd be well-advised to have a refueling plan. Push to 2+X MPG past "E" at your own risk...

The wisdom of this (or perhaps lack thereof) will be borne out only if others are able to corroborate/validate my experience. If people start running out of fuel at 1.5X MPG past "E," I'm going to feel really foolish! ops:

[cybele]

I'm curious, Eric, how your fillups were before (or even after) this experiment.

When you fill up, how much are you able to get into the tank?

I've never been able to put more than 7.4 gallons into my tank (usually 6 with a range of 250-275 miles).

We're all guessing that the bladder is more pliable in some cars and some people are able to get more gas in their tank and therefore have greater range. Of course besides your test to true empty, there is no way to test this easily.

My difficulty is believing that there is any more than whatever I put in the tank plus those 2-3 gallons in the reserve.

[ericst]

Originally posted by cybele
I'm curious, Eric, how your fillups were before (or even after) this experiment.

When you fill up, how much are you able to get into the tank?

I've never been able to put more than 7.4 gallons into my tank (usually 6 with a range of 250-275 miles).  

We're all guessing that the bladder is more pliable in some cars and some people are able to get more gas in their tank and therefore have greater range. Of course besides your test to true empty, there is no way to test this easily.  

My difficulty is believing that there is any more than whatever I put in the tank plus those 2-3 gallons in the reserve.

Oh dear, the bladder.

The tank fill-up is problematic. After click-off, I then have to carefully baby the pump. In this way, I usually can get in as much as 3 additional gallons. It's slow, so plan a few extra minutes at the gas station...

[jsorger]

Wow! Thanks! Even though I feel that driving a car dry isn't as bad when new (before the 'gunk' accumulates) I didn't have the guts to try it.
Thanks for the excellent data!

[eak354]

ukeright: blahdder! :mrgreen: