In winter, is it better for fuel effeciency to let the motor heat itself (I mean motor on and without driving) or let the motor heat during the drive ?

 

Reasonable question. The engine runs better when warm so it may be better to let it warm up a bit first before taking it for a ride.

You will get better fuel efficiency while driving if you let it warm up first, but you'll have burned more gas in the five minutes warming up than you'll save.

You can use an electric engine block heater, but it would have to be plugged in for a few hours ahead of time. That would save a tiny amount of gas, which would be good for the environment, but bad on the wallet because engine block heaters aren't cheap.

I certainly don't know the weather in all of France, but my memories of Paris in late January were that it never really got below -5C. Block heaters are more common in the very northern US and Canada where morning temperatures routinely get down to -20C.

 

That confirm my first idea, it's better to ride even your motor is cold ! but accelerate gently !!
I ask because I begin my ride every morning in town traffic... the worst case to reduce fuel consuption... and I only ride 20 km to go to my workplace... So i'm trying to find all the tips to improve my fuel efficiency

 

Hi,

It is pure speculation on my part if this helps with the HCH engine systems. We find the Prius engine has a series of significant warm-up phases:

• catalytic converter warm-up - it takes about 45 seconds for the engine running in a 'heat generation mode' to get the catalytic converters and the oxygen sensor hot enough to work. Once the oxygen sensors get hot enough, the engine mixture control feedback loop begins working and engine efficiency improves.
• coolant warm-up to 70 C - the Prius engine has to reach 70 C before efficient engine operation and hybrid control rules apply. With 0 C outside, it takes about 2-3 km to reach 70 C. During this time, I find shifting into "N" cuts the warm-up fuel burn significantly compared to "D". I prefer to cut through my neighborhood, keeping my speed about 30 km/hr or less, until the coolant reaches 70 C. Then I get on a cross-town route for higher speeds into work, 80 km/hr.
• block heater - in the Prius it adds about 20 C to the engine block in about one hour. Between 30-60 minutes achieves 60-90% of the temperature benefit. After an hour, it takes a lot longer to achieve any higher engine temperatures. After four hours, the engine temperature remains stable about 28 C above ambient air temperature.

Understand these are Prius characteristics and you really need to study the HCH systems and operation. I believe there are after-market scanners that can read out important vehicle metrics. The Honda Civic Hybrid experts would be your best bet on these systems and values.

GOOD LUCK!
Bob Wilson

 

Bob is about right about how the HCH warms up. Ideal from a fuel efficiency perspective is to be able to drive gently at perhaps 60-80 km/h directly from start. Idling is never good for FE (and not for the engine either).

And yes, the hybrid functions come on gradually as engine temp rises, after about 2-3 km. The logic is fuzzy, so it will depend on many other factors. For example, on a hot day I get auto-stop at the first red light, 100 m from the garage. On very cold days, the engine is idling at red lights even 10 km after start. When engine is cold there is regen only at higher speeds. Etc., etc.

 

Hi Rolf and Bob !

I think you're right ! I get auto-stop when the temp indicator has three bars or over, never when it is above. And I can use "EV mode" only when the temp indicator has more than 5 or 6 bars. All depend on the motor's temperature wich depends on the weather....

So in winter, during the 1st km, to reduce my fuel consumption, I let idling "tow" the HCH in "D" mode, because I'm driving in town, so my speed is low (about 30 km/h) but my instantaneous consuption is only about 3,5 l/100 km (about 67 mpg)...

PS : Thanks for speaking in metric system !! LOL

 

Hi,
There may be a block heater that works for the Honda Civic engines but it may be difficult to find. I would first research where the block heater goes into the engine. Then look for a suitable unit to fit in the car.

After I got my block heater, I took several hours to go out and measure how long it took to warm up the engine block. Knowing the power rating and the warm-up curve, I quickly figured out that:

• 30 minutes provides enough to equal about .8 km of low-speed travel, ~30-40 km/hr. This can be significant based upon your route.
• 60 minutes provides enough to equal about 1.5 km of low-speed travel.
• +60 minutes provides very little additional distance improvement.

Now this may be unique to my Prius engine but when I am in the engine warm-up phase in the 30-40 km/hr. range, I see a significant reduction in fuel consumption _IF_ I maximize use "N" versus "D" at similar speeds. I first noticed it when I came to a stop while the engine was still warming up:

• stopped at a light in "D", the mileage loss was at a steady rate
• stopped at a light in "N", the mileage loss was about 1/2 that rate

You might try a test of driving directly to a stop light or sign on cold mornings:

1. measure how fast your mileage indicator changes while in "D"
2. shift into "N" and see if the rate of change goes down
3. shift back into "D" and the rate of change goes up,

If so, you are seeing similar behavior to what I see with my Prius. NOTE: you may need to invert if using unit_of_fuel/distance versus the North American distance/unit_of_fuel.

We think Toyota puts a higher premium on engine warm-up and may be putting an additional load on the engine during warm-up while in "D". But when in "N," it can not put an additional load so ordinary, no-load idling occurs. Some of us think no-load idling warms up the car just about as fast and with a lot less fuel burn. But this is in the 10s of seconds over a 300 second interval, not hardly worth it. The extra fuel burned is not proportional to the benefit gained:


This last test was run during a typically, hot Alabama summer. You'll notice the block heater allows the engine to quickly reach a state where it will auto-shutdown. Some of our Japanese friends posted about this and they have adopted the practice of year-round block heater usage. Fortuantely, it is only needed for 30-60 minutes before starting a trip ... about the time you decide to get dressed to go, start the heater.

Now some of us have experimented with 'spoofing' the engine coolant thermistor into giving a warmer indication than the actual value. This is a rather advanced technique but simple to implement. The key to success was:

1. finding coolest, engine runs temperature - the Prius engine needs to be above 30 C and I like to use 40 C before it will run without stumbling. This is well under the 70 C when the hybrid rules are followed.
2. appropriate diode and bias resistor - the bias resistor drops the thermistor resistance giving a false, higher temperature. But we also use a forward bias, silicon diode for the 1.2 V. forward drop. This means as the engine warms up, the real thermistor value takes over so you do not get an early, "Over Temperature" indication.

I did my tests with a pot, diode and switch along with a cabin temperature gauge. When the engine reached a starting value, I would throw the switch that put the diode and bias resistor across the engine coolant thermistor. After a few tests, I figured out what works and then automated the whole thing. One of our Prius techo-fans claims to have done it with a couple of transistors but I was lazy and used a microprocessor and software.

Bob Wilson

 

One thing we do in the colder climates is to block the air flow into the rad..All kinds of methods to do this. This allows the temp to get up to operating temp. much faster. About half the time! Most people use a block heater as well. H

 

It's very interesting Bob !!! It seems you have time to experiment ! you're lucky !

 

I was late coming to hybrid ownership. In 2001, we looked at the Prius but decided to buy a 2001 Echo instead. But in 2005 when our Camry was lost in an accident, I bought a used, 2003 Prius. A lot of pioneering work had been done but there were unexplored areas. I've simply filled in some of these blanks. Actually I've had my hybrid for three years and a lot of curiosity came in part from my first, disappointing tank.

I bought our car used via Ebay in October and flew 1,300 km to drive home. My first tank gave 39 MPG (6 L/100 km.) I briefly thought about turning around and returning the car to the seller. But I knew the USA EPA rating was 45 MPG highway (5.2 L/100 km) and 52 MPG city (4.2 L/100 km.) So I spent the remaining time on this first trip to measure the mileage at different speeds and found I could meet and even exceed the EPA ratings at 105-112 km/hr (65-70 mph.)

I like to have at least two or three 'hybrid' projects at any one time and switch between them as time and resources are available. Most of my petite projects take a couple of months or longer to complete.

If I might suggest some interesting HCH projects (my apologies if the HCH community has already done these):

• battery pack repackage and split fold-down rear seat - if the passenger side rear seat could fold down, the utility of an HCH would go up for handling larger objects. The driver side, rear passenger seat could remain upright with a thicker battery pack behind it.
• mapping battery current flow and engine rpm - would provide some insights about the types of battery loads the HCH experiences. This might provides clues as how to minimize battery stress and extend the life.
• battery temperature and operation - it would be interesting to see if the HCH has operating modes that lead to steep battery temperature increases, something that shortens battery life.
• HCH emergency AC power solutions - using either the 12VDC or main battery to provide emergency house power.
• aging effects of transmission - it would be interesting to understand how the HCH transmission ages and the failure modes.

These are areas I have had an interest in the Prius community and wonder what sort of efforts might have been taken in the HCH community. Just curiosity on my part.

GOOD LUCK!
Bob Wilson

Bob Wilson