Prius vs Winter on short trips - did short experiment

For trips of less than 5 miles, it is more difficult to get the Prius efficiently running because of the hi-cost of a cold start warmup. An Engine Block Heater(EBH) or heated garage can lessen the hi cost to a cold start warmup however this may not be an option for you. Other things you can do are...

1) avoid using heater/cabin climate controls and the defroster if possible. Manually scrape off the ice/frost on the windows before driving. Chemically treat the interior of the window with defogging window treatment can limit interior condensation too.

2) during a cold start warmup-battery recharging stage - get the car moving but avoid pushing the gas engine harder than 30mph/1.10 gallons-per-hour (stay to the left of the mid-line marker on the *HSI* ECO bar) while the engine is warming up and recharging the HV battery. Why? Staying at the mid line marker of the HSI Eco bar will set the ICE at about the 1.5kwh power output level which is the Prius's most fuel efficient power setting. The warmup stage may take from three to six minutes.


3) Once the the engine fully warms up and recharges the battery, the engine will turn itself off when the car has stopped or when the driver glides by briefly lets go of the accelerator and then lightly pressing the accelerator back on (so that the HSI display is on the far left side of the ECO bar). The Prius gets its best fuel efficiency when the driver maximizes the distance that the Prius travels during these *gliding* sessions.

The Prius gets its best MPG when driven over 60 minutes per trip, on dry very smooth slightly hilly straight roads, tire pressure set to max, no stop signs/traffic lights, when the outside temperature is about 65F to 75F degrees, on sunny clear weather, running at speeds between 25 mph to 35 mph when wind resistance is minumal. Under those conditions, the Prius can get from 60 mpg to 80 mpg.

In high speed traffic on hilly terrain/roads, speeding up before climbing uphill and allowing the Prius to lose that speed while you climb to the top of the hill will help improve your MPGs.

If an when the driving temperature drops below 55 F, grill blocking could be used improve the Prius's fuel efficiency.

In congested stop-n-go traffic jams where the Prius is limited to under 25 mph when the traffic jam is likely to last longer than 10 minutes, avoid using the electric motors/battery power, that is avoid slowly pressing the accelerator slowly so that only the electric motors are used. Why? Because this ends up draining the high voltage (HV) battery if done over 10 minutes. When the HV battery power drops below 40% the ICE will agressively recharge the battery and you'll end up losing 5mpg right off the bat. Instead, press the accelerator so that the Prius gasoline motor is activated - this means the HSI indicator is slightly pass the mid point of the ECO bar. As you hear the gasoline engine start, press the the accelerator long enough to get up to a top speed (say between 10 to 20 mph) and then let go of the accelerator so the gasoline engine stop and the Prius is *gliding* with little or no electric motor assistance but not using its regenerative brakes. For this to happen, the HSI display will be on the far left side of the ECO bar but not in the recharging bar. The goal is to give the Prius an initial push strong enough to glide the rest of the distance the Prius needs to travel before it needs to stop. The slower the final speed is when the Prius has to brake and do a full stop the higher the fuel efficiency for this *go* cycle in this particular *stop-n-go* session. This technique is even more important when the Prius is stuck in an extended *stop-n-go* traffic jam in very cold temperatures because it also keeps the engine coolant warm. With the engine off in below freezing temperatures, the coolant temperature can drop one or three degrees per minute even with engine blocking. If the engine coolant temperature drops too far down then the Prius will turn on the gasoline engine just to warm up the coolant (to keep the catalytic converter warm to prevent high emission levels ). If the Prius is standing still stuck in a traffic jam when the Prius decides it must warm up the coolant/catalytic converter then the MPG penalty can be 15 mpg or higher. This happen to my Prius in the winter of 2010 when I got stuck in a snow storm traffic jam for over 45 minutes ( I achieved 22 mpg on that particular trip going home for my 16 mile commute which the day before got 55 mpg).

hope this helps

Walter Lee
2010 Toyota Prius III, Blue Ribbon/Dark Grey, Oem floormat
(aka "HyperDrive 1" on www.Cleanmpg.com's mileage log)
Yokohama Avid S33D (50psi/48psi)
100% grill blocking
ScangaugeII( FWT, SoC, GPH, RPM)
odeometer +18500 miles, overall +60 mpg