I have a curious situation that I thought the data gurus here might have an answer. Over the past several weeks here in the Salt Lake area, our high temps have been in the mid to upper 90s (with a couple triple digit days thrown in). I am wondering if high temps like these impact the operational efficiency of the EM battery.

The reason I ask, is that I appear to lose my "charge" very rapidly recently. I will go from 6-7 blue bars on the battery indicator to purple bars within a mile or so of initiating a trip. This has never occured before. This even occurs when I am exceedingly careful to maximize the amount of time the vehicle reports a yellow arrow coming from the EM to the battery (the ideal flow pattern I understand).

I also notice that when I first leave my garage in the morning (after overnight temps between 60-70) the ICE kicks on immediately even if there are 5 or more blue bars showing on the battery. I understood the immediate ICE start during the cooler fall, winter and spring months, but certainly didn't expect it during the summer months. The ICE kicks on without any use of the gas pedal (so it can't be my lead foot <grin>).

In addition, after driving the vehicle for over 30 - 45 minutes and stopping for say 5 - 10 minutes (gas station, store, etc), when I restart the vehicle, over 90% of the time, the ICE initiates again even with 5 or more blue bars on the battery indicator. As a result, I am immediately kicked out of EV only mode and as a result, my FE is negatively impacted.

For reference, I have a 2006 Prius II.

Do I have a potential issue with the MG2 battery or is this considered normal behavior for this vehicle? I don't want to take it in to the dealer unless there is a potentially serious issue developing.

Thanks for your feedback.

UTpiper

The Prius' primary goal is to produce minimal emissions. To do this it must keep the cat and engine warm. My observations so far indicate my car (Pearl) thinks 60C and above is warm (coolant temp). So whenever you start cold, the car will warm up the engine and cat by not shutting the ICE off until it starts to warm up.

When you stop somewhere, do something for a few minutes, then get back in and restart the vehicle, it will again run the ICE for a minute or two, probably to warm up the cat (I can only monitor the ICE temp., not the cat temp, and the ICE was still fairly warm), but it will shut down much quicker than if it was cold.

As far as battery operation in extreme temps (90F and above), the system will try to protect the battery. It uses cabin air to cool the battery, so use your A/C to give it cool air. NiMH batteries have a negative temperature vs voltage response, so a hotter battery will have a lower voltage. Combine this with the higher voltage at higher charge, throw in the possibility of incomplete compensation, and you can see how the SOC meter could be confused. It's probable the system is more careful with the battery when it's hot. Not charging it as much and not using it as much. This is because using or charging it will result in more heat.

Pearl is a
2007 Driftwood Pearl Prius
Package "B" (everything but leather, nav, and rear camera)

Hi,

This may help with some insights about coolant temperatures and ICE operation:

http://hiwaay.net/~bzwilson/prius/pri_temp.html

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Thanks for the explanation. This makes sense and since my garage doesn't exceed 30C (even on the hottest nights) the engine is going to have to run in order to get up to the 60C - 70C minimum when I get going in the morning.

UTpiper