Hybrid Car – More Fun with Less Gas

Cold weather and the Prius skeptic

register ::  Login Password  :: Lost Password?
Posted by bwilson4web on September 21, 2011, 1:48 pm
Prius cold weather performance has been the straw most often grasped
by hybrid skeptics. The 1.5L Prius take pains to minimize emissions
and engine warm-up and this burns more gas, often inefficiently.
Worse, at high power settings, the 1.5L engine uses fuel enrichment to
avoid burning out the catalytic converter. It didn't take long for
petroleum addicts, petrodicts, to decide this would be their 'hook'
for Prius critical articles.

The first I remember was a Car and Driver article that decided the
middle of winter was the perfect time to do a highway, comparison
drive between a Prius and Jetta diesel. A more blatant effort was the
"Green Human" Portland-to-Portland, 8,000 mile, cross-country USA
drive between a 1.5L Prius and Jetta diesel. But in the end, there was
only a 0.5 MPG difference between the larger, roomier Prius and the
compact Jetta. Even now, hybrid skeptics trot out the 10 F blizzard on
the highway as their metric for Prius performance as if that is the
only metric that counts.

Now the 1.8L Prius introduced two technologies that directly address
cold-weather and high-power performance:
This image shows the collant pipe from the exhaust heat exchanger. So
instead of de-tuning the engine to accelerate engine warm-up, the
waste heat downstream of the catalytic converter is captured and sent
to the engine block. A by-product is during winter operation, this
formerly waste heat preserves both the engine block heat and provides
excellent cabin heat.

The second technology is:
This image shows the 5th tube on the exhaust manifold that routes
exhaust gas to a cooler before it feeds into the intake manifold.
Cooled, exhaust gas recirculation means at high power settings, this
inert gas cools the exhaust to protect the catalytic converter. The
engine does not have to run an over-rich mixture. Effectively, these
two technologies have eliminated the 10F blizzard from the petrodicts
criticism . . . except for those still thinking the 1.5L Prius is the
only benchmark. But there is one area that the 1.8L Prius needs to
further improve high-speed and cold weather performance.

One of the earliest owner mods is to block the radiator air inlet.
This reduces cooling drag, improves warm-up, and reduces vehicle drag.
The Chevy Cruz Eco uses variable vanes and in Japan, Prius owners can
buy an after-market, variable air inlet kit. With the return of Fall
weather, I've put my duct tape wrapped, pool noodle back in my 1.5L,
2003 Prius to preserve summer mileage. By careful measurements last
winter, there was a 5% improvement in mileage using a whole, air-inlet
block in my wife's 1.8L Prius.

About three years ago, we had a record setting, cold air system come
to Dixie when I needed to drive to South Carolina to buy a failed
traction battery. The high pressure center was over Atlanta, midway in
my trip. I left at 4:00 AM, 15F and by the time I reached Atlanta, it
had not reached freezing. It wasn't until 2:00 PM when the temperature
finally reached 37-38F. I picked up the traction battery and by the
time I returned home at midnight, it was back to 18F.

I kept my speed constant 65 mph on the highway and measured the
mileage over different temperature ranges only to find later that the
mileage followed the air density as a function of temperature. The
highest milege was 49-50 MPG at 37-38F and 65 mph. Other segments were
down as low as 34-35 MPG solely due to the higher air density of cold

The 1.8L Prius could be improved with variable, cooling air inlet
vanes. But compared to the 1.5L Prius, it is substantially improved
with exhaust warmed coolant and cooled exhaust gas recirculation. We
see this in the average mileage owners report for the 1.8L Prius over
the earlier 1.5L Prius. Petrodicts are left with crying over the 1.5L
Prius in a 10F blizzard.

Bob Wilson

Posted by News on September 21, 2011, 2:09 pm
On 9/21/2011 9:48 AM, bwilson4web wrote:

Does thin skin run in the family?

Posted by Elmo P. Shagnasty on September 21, 2011, 2:43 pm
 In article

you know, because actual facts--like my observed fuel economy this past
winter--are immaterial to people like you.

Posted by Elmo P. Shagnasty on September 21, 2011, 2:47 pm
 In article

Which leads to some questions, such as:

* why didn't Toyota engineer this as a standard feature?

* can/will Toyota use this "owner mod" as a reason to void any warranty

Posted by bwilson4web on September 21, 2011, 4:07 pm
 Well, my posting seems to have woken some folks up:

Facts and data often drive hybrid skeptics into ad hominen postings.
So collecting the more recent 'skeptic' laments in one thread is an
effective technique.

As my first posting shows and other studies not yet cited, I do study
Prius cold weather performance. For example, my earliest transaxle oil

I use metrics to obtain facts and data as there is a big difference
between "anedotal" reports and an engineering analysis with hard data.
The former often come across as whining whereas a reasoned,
disciplined study can provide insights to mitigate a problem. When
someone is in darkest ignorance, I'm not one to complain, much, but
rather prefer to "light a candle" and learn something useful.

I have no idea but that that is not unique to Toyota. There is a huge,
after-market for just about every vehicle that has ever been made
ranging from turbo-chargers to anything that can be bought and
installed on or in a car. The generic version of this boring question

"Why didn't [any manufacturer] engineer this as a standard feature?"

They didn't so owners and enthusiasts fill in the answer and are
thankful for the business opportunity.


I was concerned about this so when I bought my 2003 Prius with 49,000
miles, I held off on any changes that might impact the 60,000 and
100,000 mile warranties. But adding a 1 kW inverter did not touch
these other systems and was my first modification. Once my car passed
those later milestones, I was free to make any modification I wanted.
So last November, I upgraded my traction battery to NHW20 style

A warranty has value and I would recommend anyone wishing to make or
test a modification to be very cautious until the warranty period is
over. For example, my wife's 2010 Prius bought in May 2009 has the
3/36000 warranty until June 2012 or about nine months to go. Once her
car passes that threshold, I'll put in the 1.5 kW inverter and may
upgrade her 12V battery. Other modification will wait until the drive
train warranty, 6/60000 and traction battery/inverter warranty,
10/100000 have passed.

Bob Wilson

This Thread
Bookmark this thread:
  • Subject
  • Author
  • Date
please rate this thread