Car Loses MPG as it Idles when in Traffic... Any Suggestions?

When the ICE (Internal Combustion Engine) is not running, your Prius is drawing power from the HV battery. You see great mileage at this point because the mileage calculator does not account for battery use. Essentially you are borrowing energy that must eventually be paid back with interest. It's like living high on the hog with your credit cards, but eventually you have to pay the piper.

In your case paying the piper happens when the ICE kicks on to recharge the battery. If you are driving at speed you don't notice it since the ICE is used a lot to provide power. In stop and go it becomes obvious since it seems weird to hear the ICE working hard even though you aren't going anywhere. All it is doing is replacing charge in the battery, and generating heat to keep itself warm. Using cabin heat also requires the ICE to run more to make heat.

Tom

 

If you set the MFD to show the HSI display, you can see the HV battery level. If you are sitting in traffic and this gets down to 2 bars, the ICE fires up to put charge back in the battery. Would be worth confirming that this is the case with you. Chances are that after 15 mins in start stop traffic with heating or AC on, you are going to be pretty close. The longest I have managed is 25 minutes. On the plus side, think what the fuel consumption would be like in a normal car.

Or it could be you have rested your right foot on the gas pedal? I did that once and the ICE fired up !

 

You can delay it by not using A/C or defrosters, but if you're in solid traffic it's pretty much unavoidable, IME.

 

It's just normal. Mostly happens in warm up mode and/or when the heating is required or if the battery runs down too low. I often find this if I am stuck in heavy traffic for too long. That's why my fuelly figure is so low compared to other Prius owners, but it is more than 40% higher than I got out of an European eco diesel!

It does break my heart when I've run up a great mpg figure and then find that it is slowly destroyed by the car idling in traffic. What you just got to remember is that you will still be using much less fuel than if you were in a 'normal' car.

 

I drive mostly in London and this happens all the time, sitting in slow traffic for more than 4 minutes kills the battery and the engine comes on at full revs for a minute. I've found its possible to stop the ICE by putting it into EV mode while stationary, but if the battery is down to 2 bars this doesn't always work.

 

You know those times when your Prius is idling, wasting gas while stuck in traffic? All of the other cars are also wasting gas idling while stuck in traffic, but they don't shut off when the battery is charged up again. :madgrin:

 

As always 'qbee42' has the right answer.
That also happens to me when the battery is weak (2 lines).

 

If you are parked in traffic or just creeping along sooner or later the ICE will have to kick in to get back to operating temp or charge the traction battery. Then it runs for a very brief period, shuts off, and repeats which is very annoying. Reducing the electrical drain will help delay the situation. Happens to me in the Lincoln Tunnel traffic.

 

Suddenly, it occurs to me that, I have never been stuck in traffic in my Prius. I feel better for having read this.

 

So far, it doesn't seem like anybody has posted a particular way to avoid this - just the reason why it's doing this.

My personal recommendation would be to try accelerating more sharply in such situations, at least occasionally; at least a little bit past halfway on the HSI. That will cause the engine to come on to move the car forward rather than draining the battery so much, and extra engine power can be used to charge the battery at the same time. This might be more efficient than having the engine come on when you're at a full stop.

Of course, the usual caveats apply - only do this if it's safe. And I'm sure somebody will chime in with a different opinion as well...

 

The control system on the Prius does a pretty good job coping with stop and go traffic. The loss of efficiency from running on battery power is offset by the low efficiency of an ICE at low power levels. This is an example of "pick your poison", and the system does alright with it.

My advice is to not worry about it, but simply understand that sitting in traffic is not good for mileage.

Tom

 

Probably many of us have seen in the HSdisplay, the arrows draining battery many times...
In traffic jam/stops, if the brake pedal is not "fully" depressed, my MY10 shows that energy flows is not stopping. Often (traffic crawling) I prefer to come to a stop with a "more" vigorous way, interrupting crawl. As far as I remember, crawl mode drains 600W continuously.