EV mode Vs. Running out of gas

When in EV mode, the ICE will turn on when the traction battery needs to be charged.

If you run out of gas and continue to drive merrily along, the traction battery may be drained below 40% SOC which is the minimum charge allowed by the battery ECU.

 

I imagine the battery could handle a half mile...

 

Some people report having done just this and hosing their battery pack requiring a relatively expensive "reconditioning" at the dealership. I've done it once (didn't make it to the gas station though, it was too far away) with no ill effects. <shrug> The best advice, of course, is to just tank up as soon as you possibly can after the last pip starts flashing. I was one of those who used to push it, but that finally caught up with me. Don't get complacent just because you get great mileage. Fill up when the car tells you to.

 

As the other posters have said, the difference is with options. Without fuel the Prius cannot start the ICE when it needs it. That's the short answer.

The longer answer is it depends on several factors, such as battery temperature, SOC, power demands, and distance. A short distance will not cause any harm, but the question becomes one of defining short with all of the complicating factors. Even without the ICE, the Prius will do its best to keep you from hurting the battery. It takes some determination to run the SOC down to an unsafe level, but why risk it.

I haven't run my Prius out of gas (yet), but if and when I do, I'm sure it will come down to a judgment call: If the gas station is across the street, by all means I'll drive over. If it's a bad neighborhood, I may push it a bit farther. If I'm on the highway, I'll drive to the shoulder and stop.

Tom

 

As I stated in another thread (in another universe), if your battery pack is relatively new it is unlikely you could cause any damage to the pack, no matter how hard you try.

If the ICE has fuel the lowest you can discharge the pack is to about 35% charge, even in "EV" mode. If the ICE has no fuel, you can get the pack down to about 30% charge, perhaps a bit lower, before the car's systems "shut you down". BTW, this "shut down" is an important warning owners should not ignore! DO NOT try to restart the electric mode after it shuts you down. You have gone as far as you should. Walk the rest of the way for gas!

The danger is if one or a few cells in the pack have a lower capacity than the others (or are simply running at a lower charge level). They will fully discharge first, perhaps before the system realizes the pack is getting low, so it doesn't shut you down yet. If you then continue on electric power you will "reverse charge" those cells, and that -can- destroy them. As a new pack is probably very well matched, cell to cell, it's unlikely you could damage it. Once the pack gets older, the cell capacities can drift for many reasons (electrolyte leakage, pack loss of "equalization" etc), and it is then that some cells may be in danger if you push it.

So don't let the car run out of gas! Very simple solution!

 

The difference is that with the EV button the car is still actively managing the battery's state of charge; when you're out of gas it is not. Driving on battery only when out of gas can reduce the total battery life by some fraction, but it might be the lesser evil in some situations. Best never to run out of gas in the first place.

 

Well I ran out today. I have been driving west from Eastern Shore of Virginia with my oldest son and my new prius. We hit New Mexico on route 40. Cruising at 80..... I looked at the bars there were two. A couple minutes later there was one and a beep. I falsely assumed I would get 6 more miles down the road. At about 2 miles the engine shut down. I drifted and ev'ed within a mile of a gas station. Fortunately there was a place full of old studabakers on the south side of 40. I crossed the hi-way with my teenage son, climbed my fat nice person through some barbed wire and walked in to the studabaker junk yard. Danny owned the place and gave me a jug with a gallon in it. Having read all the doom and gloom letters about running out I was apprehensive at best. I put the fuel in. Hit the power button and let it sit for a couple of minutes to charge the fuel system. It started on it's own. I climbed in hit the power button again, put it in drive and put 10.9 gal in. Plus the gallon from danny = 11.9. 435 miles on that tank. All the warning lights went out and there was no problem. I immediately went to walmart and bought a 1 gal jug. I have never run out of fuel in any car I owned. I expected a bit of a buffer when the beep and the bar started flashing... Not much of one. Lesson learned. The good news is we filled Danny's jug, then stopped and sat in his shop. We had a great parle! He sent us to stay with some friends of his that own a funky old Rt 66 motel called the Blue Swallow. It was a great stop in Tucumcari New Mexico

 

All's well that ends well. (And fer gosh sakes don't carry a filled gas can around in the trunk.)

 

That's right: set that fuel can on the floor on the passenger side. It makes a good place to rest your cigarette.

Tom

 

Further more..... Yesterday I had my friend and his wife in the car. We drove east from Santa Barbara towards the wine country. I sat in the back seat and let his wife drive the car. I looked over her shoulder and saw 2 bars on the fuel gauge. I asked how far till the next opportunity to fuel and was told 20+/- miles. Suddenly it went to one bar. I was tense to say the least after running out in New Mexico. I was furious with myself for not topping off. Just did not think about it from the back seat. In any case it quickly went to 1 bar and I started sweating bullets. We got to a fuel station and the car only took 8.7 gallons..... Wait a minute I thought. Last time it went bone dry within minutes. This gauge has me spooked at this point. I did a little reading in this forum, and who ever coined the phrase "guess gauge" hit it right on the money. My friend was surprised that there was no countdown/miles left on the trip computer like his subaru has. Got me thinking.. Yeah.. why not!

 

Thanks for the belly laugh Tom you sh!t stirrer.

Leave the extra fuel can at home and fill up at 2 bars.

Battery damage comes if you restart after the car stops on batteries and keep going. You may do some minor harm driving until your prius stops.
The reason you can restart is it allows you to move in am emergency like it stops on a railway line or something.

I just think it's best never to run out.

 

It would be worse than useless because it would give the driver a false sense of certainty. The amount of fuel still *available* in the tank is too hard to know, and the fuel economy you are going to get in the immediate future is obviously impossible to predict.

But what about people who don't smoke?