2009 Prius Base - $19k - Page 19 - Fuel Economy, Hypermiling, EcoModding News and Forum

Matt Herring · 07-06-2009, 06:58 AM

Pulled my grill block on Sunday...temps were above 80 and I didn't want to push it. With the grill block removed I have to get my EBH installed to counter the deleted mod. After EBH is installed I'll remove upper grill block. Hey, maybe this will change the weather karma and give us some better temps and NO RAIN!

Filled up this morning and pushed the gas tank alot further than I wanted to. Drove over 500 miles on this one but was down to 1 Pip and fully expected to see it flashing before I got to the gas station. I wanted to fill up at my regular gas station so I put another 30 miles on the tank with 1 Pip left...when I got to the gas station they were still closed so I had to go another 5 miles on 1 Pip...sweating heavily I made it to the next station.

Daox · 07-06-2009, 07:14 AM

I think you're okay until the 1 pip starts flashing. Then its time to get gas NOW. At least thats what I read on priuschat.

Matt Herring · 07-06-2009, 07:23 AM

I drove about 35 miles on the last Pip so I knew I was close...no flashing Pip but at that point it's danger mode. Many have driven on the flashing Pip and hurried to get gas but it's a couple hundred dollar mistake if you run out of gas. The fuel system has to be reset and it's costly.

When I got to my regular gas station this morning and it was closed I dropped it down under 41 mph and just used the battery as much as I could until I got to the gas station about 5 miles down the road. Luckily, this was at 6am and there was little traffic so I crawled to the station just to be safe. Had the Pip started to flash I might have used the battery even more.

PA Prius · 07-06-2009, 07:59 AM

Quote:

Originally Posted by Matt Herring

... I had to go another 5 miles on 1 Pip...sweating heavily I made it to the next station.

We fill around ten miles after the start of the blinking pip and are still only able to get 7.x gallons in. Three-plus years, 73,000 miles and we haven't ran out of gas yet.

PA Prius

Matt Herring · 07-06-2009, 08:20 AM

I filled a little over 9 gallons this morning...but would rather not risk waiting for the blinking Pip to do it...there's really no reason to wait that long. Even if you're getting 7 or 9 gallons in the tank it's not realistic to think you have 2-4 gallons still in the tank when the last Pip is flashing. There's a good chance there is well less than a gallon in there and 10-15 miles down the road it could be completely empty (or sooner).

When I had my 4runner I tried to stretch the tank as far as I could going for a 500 gallon tank but the consequences of running out of gas were far less damaging in the 4 runner vs. the Prius. Drain it dry in the Prius and it's alot of money and time to get it repaired.

I usually fill up with 2 Pips left and that's it.

MetroMPG · 07-06-2009, 08:57 AM

Matt - why is running out of fuel damaging to a Prius?

I'd read that diesels may require a trip to the shop if they were run dry, but not gasoline vehicles.

Matt Herring · 07-06-2009, 09:05 AM

The problem with running out of gas in the Prius is a complete system failure. When you run out of gas the ICE is completely out of play and then the car switches to battery power. If you are close to the station you can try to make it on battery alone but it will discharge at a breakneck rate...recommended to shut down all power draining sources including lights, air, radio, etc. If you run the battery completely down you are risking serious damage to the Prius...aka...completely out of gas and dead battery. Now you are in the "flat bed tow to the shop for recharge" zone. Also, the Prius battery has to be "jumped" in a very specific way...highly recommend you do not do it yourself unless you completely understand how to do it (never let a tow donkey with no Prius experience do it on the road).

There are plenty of people that have run it dry more than once...but the risk of damage in the Prius is much higher than a regular ICE vehicle.

MetroMPG · 07-06-2009, 09:16 AM

OK, but nothing inherently damaging about running dry. Only if the driver continues blithely pushing onward under battery power alone.

It's surprising the standard programming in place that normally protects the NIMH battery by managing its state of charge "window" doesn't continue to protect it in a case where there's no gasoline.

So there's nothing to prevent it being fully drained if you keep driving with no fuel on board? (Doesn't it operate with something like a 40 or 60% lower limit on SOC in normal operation?)

Matt Herring · 07-06-2009, 09:28 AM

A driver can run the gas and battery dry and the Prius system will do nothing to prevent it. When the tank has gas in it the battery is protected by the system with ICE-driven battery charging. Near 3 bars the ICE will begin sapping power to recharge the battery and below 3 bars the ICE is running to do this.

At/near/under 3 bars when this is occurring you will notice a heavy toll being taken on the horsepower of the car as the ICE splits its output between charging the battery and power to the wheels. If you're going uphill when this is occurring you will often get a revving of the engine (as high as 2500) when normally it is running at 2000-2100. This is the paradox with driving in EV mode as you cannot do it too much because eventually it will take ICE to recharge it (wasting fuel in the process).

On a side note...

Initially, I thought driving as much as possible in EV was the way to go. Why not...the less gas and more battery I use the better right? Wrong. Some EV driving is good but you have to make sure you know where you are going to recapture that energy to keep ICE running efficiently. If you have plenty of downhills with ICE or braking to recharge and not tax the battery that's fine. But, running EV all the time will eventually cost you FE.

This is particularly present with the EV switch. I recommend only using it at the end of a commute when the Prius start up cycle will recharge the battery for you the next time you start the car. Running EV and draining the battery in the middle of a commute will cost you FE if you run the battery too low and force ICE to recharge it for you. No doubt, the EV switch will help FE but only if used correctly. Daox should provide some good info. on this when he has some time to get the highest efficiency out of his.

MetroMPG · 07-06-2009, 09:48 AM

Ironic isn't it, that generally the most fuel efficient way to drive a hybrid is to minimize use of the electric motor for both propulsion and regen.

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That's REALLY interesting that Toyota didn't include failsafe protection for the NIMH pack in the event of running out of gas.

Maybe they did it for legal reasons:

Imagine if a Prius ran out of fuel and then got creamed by a truck because the software shut it down when the driver was still trying to press on. Flattened like a pancake even though there was still "plenty" of energy remaining in the battery to drive the car! In some litigious locales, I'm sure there are lawyers who would love to get their claws into a case like that.