I am trying to figure out the best method for driving during the early warmup period of the Prius.

When the car is powered on, the gas engine warms up. At this time, if you watch the MFD you will see the MPG dropping slowly during this period. So obviously gas is being burned at this point.

My question is, is it better to sit through this period and then optimize stealth mode driving at low speeds [if your commute allows for it] or should you begin driving as soon as the Prius is in ready mode?

I think most of you know that driving as soon as the Prius powers on results in very low MPG during the warmup period. I usually see about 10mpg or so during this time.

So is it better to drive during this period, or let it warmup and then begin your commute?

 

In my case, I have a Graham scanner and can monitor the intake air grams/sec. I get the car rolling at about 15 mph and then use "N" to coast down a gentle slope on my street. Thereafter, I'll accelerate to ~20-25 mph and use "N" to coast down to 15 or so while the ICE continues to idle and warm up. Once the ICE airflow at idle drops below 2 g/s., I'll accelerate to 35 mph where it is safe and verify the ICE auto-stops. This means the car is in hybrid mode and I can head for faster streets.

Actually, I head for access roads that allow me to cruise in at 38 mph. This gets me into work reasonably fast and efficiently. However, this morning I had a chance to try my new block and transaxle pan heater.

The initial results suggest it cuts the warm-up period to about 1/3d of normal. There is still some tweaking and testing to do but it definitely helps. When I put my modified thermistor hack back in, I'm anticipating a significant improvement (along with Type WS in the transaxle.)

Bob Wilson

 

Thanks for the reply Bob!

When you are referring to "N" are you referring to actually shifting into N with the gear shift, or the black arrows on the MFD indicating you aren't using gas/battery/recharge?

Also, in regards to the heat block, how did you install this? Was it complicated? My car is outside at work during the winters here in VA, and there will be a few weeks where it won't get out of the uppers 20s and low 30s. I am interested in optimizing my MPG, so if an engine block heater is the way to go, I am interested in how you installed it.

Also, in regards to you driving immediately, unfortunately I am stuck in a situation where as soon as I exit my neighrborhood I am instantly on a 45mph road, so if there are cars coming I have to move relatively quickly. Otherwise I can take my time and let the battery get me up to speed before I hit the first stoplight.

 

I just go unless it is extremely cold out. I figure if the gas engine has to be turning to warm up the system, it may as well be propelling me on my way to the destination.

 

I'm using the ICE airflow in grams/sec to monitor fuel consumption. I've found the absolute, lowest 'idle' fuel burn is in "N". There is no accelerator trick that beats "N" for my NHW11, 2003 Prius.

http://www.techno-fandom.org/~hobbit/cars/heatgames/

The only 'lesson learned' is getting the heater element latch works a lot easier with a pair of pliers. When you get there, you'll understand. It is roughly a 30 minute to an hour job.

The block heater would help reduce that fuel burn.

Bob Wilson

 

Thanks for the link to the engine block heater!

 

I haven't yet experienced winter with Pearl, my 2007 Prius. Currently, after parking overnight (or longer) in the garage, the engine starts just as I back out, and quits after I close the garage door and enter the car (coolant at around 50C). So it runs for 30 sec to a minute. It starts again when I depress the accel. pedal in "D". So how do I wait for it to "warm up" if it doesn't? I still see the 5 min "warmup" hit. Seems so far, I get that after the car is off for about an hour or longer.

I may start using the block heater to see if it helps. It's hard to plug it in when it's 30C out!

 

The engine block heater for a '04-'07 Prius is part number 00113-00213-00889 in the US, CO140-00889 in Canada.

Using a block heater in the summer months for 3 hours before departure will usually give you a engine temp of between 135F-145F. That will drop in the first minute of ICE on as cooler coolant circulates and then pop back up. Within 3-5 minutes your over 155F which should put you in full hybrid operation (stage 4). The first 5 minute consumption screen should nearly double depending on your driving conditions.

Wayne

 

Maybe I'm missing something? I drive immediately (0 on speedometer) at all times of year. Running the engine at 0 mph for the time it takes to warm up to complete seems like a waste of energy to me.

 

The initial ICE warm-up can be pretty brutal if you have a heavy load (aka., climbing a hill out of the driveway) If you can use a block heater to warm the car and then let it sit in the driveway without a load until auto-stop, you can then assault the hills with an efficient engine. The MPG won't be great but as we used to say in the Marines, "It s*cks less!" But this is hopefully, a rare situation for most folks.

Bob Wilson