By on January 8, 2010

No relation... (courtesy:HP Eyeonblades blog)

TTAC Commentator writes:

So, today I passed a guy putting gas in his Prius on the side of the road. I assume he ran out of gas. Irony?

My question: can a Prius run on just battery power when the gas tank is empty? And if this guy ran it out of gas AND drained the battery, was he FUBAR? I assume it has to have a good battery to run, gas in the tank or not.

Sajeev Replies:

The short answer is yes: according to this Prius owner it can go a couple of miles on battery power alone. But the Prius isn’t supposed to run like an EV: running a Hybrid on empty is murder on a battery pack. Most, if not all, batteries do not play nice after running below their voltage range. In the case of a Prius (according to Google) that is 273.6 volts coming from 228 batteries with 1.2 volts each.

The question is, at what voltage does a gas-less Prius resign: completely taking a dump, telling its owner to go pound sand? Conversely, will a Prius save itself to live to fight another day?

Because if it will not, the battery pack is Tonya Harding’d and on a short and painful road to the recycling center. See the “Over Discharging” section of Wikipedia’s Nickel-metal hydride battery page to see how/why this happens.

Don’t you just love it when answering a question opens a whole new can of worms?

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26 Comments on “Piston Slap: Long Term Ramifications of Prius Abuse?...”

  • avatar
    Dave Skinner

    It’s a non-issue. While the control system may not allow battery power to propel the car any longer, the engineers make sure to shut down propulsion long before high voltage battery damage occurs.

    The system is far more sophisticated than the contacts in your ignition switch which allow syou to crank a no-start engine until you damage the 12 volt battery (or cook the starter…).

    I can’t speak to Toyota’s hybrid system, but Honda includes a 12 volt back up starter in their models, which will start the IC engine if:

    1) The high voltage battery charge cannot start the engine

    2) Ambient temperatures preclude the use of the high voltage battery.

    Belts and suspenders.

    • 0 avatar

      > 1) The high voltage battery charge cannot start the engine
      Prius has a conventional, albeit small, “12V” auxiliary battery used for starting. It’s in the trunk, so it requires special venting.
      I believe that US versions of the Prius will not run electric-only, but European ones will, allowing them to be used in (urban) zones which restrict ICE vehicles.
      Such zones are uncommon in the US, so deleting the option might favor the longevity of the high-voltage battery. Makes for fewer “hidden cost” stories in the media.

  • avatar
    Paul Niedermeyer

    I can’t imagine that the Prius’ battery isn’t just as safely protected from excessive discharge regardless of whether the gas engine is running or not. To keep the pack healthy for so long, the Prius only uses 20% of its capacity, from about 80% SOC to down to 60%. There would have to be some failure in its protective circuits or meddling to go below that.

    • 0 avatar

      True, Paul, true… BUT…
      I cannot imagine that Toyota would ever mess up something as simple as the steal used in a pickup truck frame that could lead to a massive recall.  Honest.
      Wink, Wink, Nudge, Nudge.
      And see… I managed that without even touching the “sudden acceleration” issue…

  • avatar

    Edmunds intentionally ran their 2004 Prius out of fuel to see what would happen:

    “Once the gas finally ran out, the engine shut down like it normally would, but a myriad of warning messages and lights filled the instrument cluster. I had just pulled into a quiet neighborhood with no traffic, so I continued to drive very carefully under battery power alone. This lasted all of a half mile, probably because I had just been sitting in heavy traffic with the A/C blasting (the A/C is powered by the hybrid battery). I coasted into an empty driveway as the car completely shut down and added my gallon of emergency fuel.

    “The Prius fired right back up just as if nothing had ever happened. The hybrid battery gauge was lower than we’d ever seen it, but the car drove away without fuss. The engine revved higher for a few minutes, working to recharge the battery, but otherwise all was fine.”

    No long-term effects on the battery were noted, but they only kept it a few more months.

    • 0 avatar

      Half a mile of battery power is better than nothing.   It gives you some choice of where to pull over, and might even get you to a gas station if you’re lucky.   And despite Toyota’s many documented product goofs lately, I’ve got to assume that the car shuts down before battery damage can occur.
      That said, if I ever pass an out-of-gas Prius in my gas-chugging CUV I will surely give the driver a thorough taunting.

  • avatar

    It’s my understanding fuel pumps shouldn’t run dry.  If that’s the case, the expensive repair he has coming up isn’t the battery, it’s the fuel pump.  The control system won’t discharge the battery so far as to damage it.

  • avatar

    TTAC has a decent amount of traffic right?  Can’t Bertle just call the Toyota press office and have them ask one of the Prius software engineers?   I’m sure there is a couple of lines of code that deal with how the hybrid system should react to a no-fuel situation.

  • avatar

    on a conventional ICE, I don’t think running out of gas necessarily ruins the gas pump. I seem to recall my mother running out of gas, back in the late ’50s or early ’60s when cars weren’t what they are now, and I don’t recall ever having to fix the fuel pump on the ’57 Chevy. And, ***I*** recently ran out of gas for the only time in my life (right next to the gas pumps at a Shell station, which was ***closed*** so I had to call AAA and wait 40 minutes) and nearly a month (and probably about 1,000 miles) later, no problems.

    • 0 avatar

      My understanding, which may be flawed, is that the fuel itself helps cool the pump in the newer designs and letting the pump run dry might allow it to overheat.  I think Volvo was an early adopter of a pump-in-the-tank design and I was warned not to let the tank go dry.

      Of course, “Don’t run out of gas” is good advice in so many ways.

    • 0 avatar

      Your mother’s carbureted ’57 Chevy had a mechanical fuel pump, which is basically a rubber-diaphragmed bellows connected to a rod. These are located in the engine compartment and “pull” the gas from the rear-mounted tank.

      Modern, fuel-injected vehicles (and a handful of older ones with carbureters) have electric fuel pumps that “push” the fuel from the tank. The electric pump gets warm and may rely on the liquid fuel to cool it. Running out of fuel – particularly if done repeatedly – is problematic in two ways, as it may cause the pump motor to overheat and could allow collected junk in the bottom of the tank to foul the fuel system (both scenarios depend on design, condition of the fuel system and other factors such as ambient temperature).

      That being said, I ran the tank dry on my 2000 Ford Ranger when it was relatively new (I’ll admit I’m a dufus…it was used occasionally and lacked a “low fuel” light that all of my other vehicles had since the mid-’80s) and it’s still running on its original fuel pump with over 100k miles.

  • avatar

    The point is, the picture shows a Prius owner that ran out of GAS.
    That’s all the irony I needed.

  • avatar

    Running out of gas with an electric, in-tank pump can damage the pump.  I’ve heard it relies on the fuel for lubrication and cooling, so if it’s pumping air it’s running hot and dry and that reduces it’s life.

    The F-150 with twin tanks supposedly has lots of fuel pump problems if the owner routinely runs the tanks empty before switching.

    • 0 avatar

      I’ve heard that too, but I’ve seen so many cars with empty tanks and their pumps lasted longer than the owner’s interest in the car.  I guess you gotta run it dry several times before something bad happens.

  • avatar

    Let’s go to Toyota’s website and see what they say:

    Can Prius run on electricity when it runs out of gas?
    No. Though Prius can operate in electric-only mode when gasoline is in the tank, it is not designed to run without gasoline. Doing so could cause severe damage to the hybrid system, so drivers should be sure to keep gas in the tank at all times.

  • avatar

    With the the Two-Mode system that GM uses, I believe that “all reverse operation is driven by the electric motors.”
    So does that mean I could go in reverse with no gas in the tank? How far could I go?  What if I had gas in my hybrid SUV but just drove for miles in reverse?  Could that kill my electric motor? Can I take advantage of regenerative braking and drive forever in reverse without ever using gas?

  • avatar

    I call this a staged photo.

    • 0 avatar

      It could be staged, but it is easy to run out of gas if you are coming from a relatively thirsty car with a relatively small tank to a Prius.   Yeah, I ran out of gas the first month I had my Prius, I was used to having to get gas every week in spite of my short commute, and when you can go 600 miles on a tank, it’s easy to forget.    It went for about 1/4 mile on the battery.   That was five years ago, no damage to the system that I can tell anyway.

  • avatar

    A couple of weeks ago I saw someone putting gas in a Prius at the side of a road in Salt Lake City, so this guy wasn’t the first.

  • avatar

    Forget the Prius. Which make is that nice looking white truck in the background?

  • avatar

    While  I’m sure that running a fuel pump without gas to lubricate and cool it is bad for it, how long would the pump actually be running in such a condition? On any injected system, it seems to me that the pump would prime for 5 seconds or so when you turn the key to run, and then run for the few seconds that you’re cranking the engine. At any other time, the ECU should sense that the engine isn’t turning and therefore not energize the pump. How much could a little pump overheat by occasionally running dry a few seconds at a time? When you start a cold engine, you’re basically turning it over unlubricated for the couple of seconds until oil pressure builds, too, and that’s a completely normal operating condition.

  • avatar

    I can understand this, as I have several Jeeps that get 14 to 17 mpg vs. my daily driver a Civic that gets 34 mpg and sometimes I just push it with Civic thinking it can go a little longer (I like to hit 400 miles per tank). With the Jeeps, I’m just use to filling them up. (lol)

  • avatar

    i know voltages don’t compare, but after my experience with R/C cars, discharging batteries NiMh batteries helps extending their lifespan.
    in any case, my 7.2V 3000mah packs were used always to almost complete discharge, that was the rule to keep them for longer anyway…unless the people that told me so were wrong in the first place yaykes….

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