Stuff you can do to improve your winter mileage

If you have an aftermarket device, like ScanGauge, watch for 145°F.

When the coolant temperature drops below that, the engine will start back up. Until then, you can take advantage of the Max Hot setting with the blower on a low speed.

It's nice knowing exactly how much heat is still available when sitting there waiting for the stoplight to change.

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The EBH isn't very powerful at 400W.

Did anyone add a ~250W oil-pan pad heater to pre-warm the engine even more?

such as this one:

http://www.warehouseautoparts.com/Specials/Kat/Kats_24250_oil-pan_heater.htm

The warehouseautoparts site indicates that the 100W heater should be used for oilpans with a capacity of 2-5 quarts. (the Prius takes 3.5 to 3.9 quarts). The 250W heater is recommended for oilpans in the 8-20 qt range.

Norm

Good point, I didn't verify that.

This is one of those half-thought-out ideas so bear with me.

Has anyone considered mounting an electric ceramic heater between the grille and the radiator, connected to the same timer as the EBH? With grille-blocking, it should provide some general pre-warming to the coolant in the radiator as well as the engine compartment.

We've had a cold snap here in PA (morning temps around 26 degrees F) and I was disturbed to find my scangauge reading a low 85 degrees (normally closer to 120 degrees until now) when the ICE first powered up.

Any thoughts one way or the other?

Although I don't make a lot of 30+ minute trips, I've noticed that when I do, there seems to be a slight boost in efficiency beyond the 30 minute mark. Without any empirical evidence, I've attributed that to the entire HSD reaching thermal equilibrium, as opposed to only certain components achieving a minimum level of efficiency. (This would be during mild to cool ambient temperatures.) So the theory is that warming the other components of the system would help simulate that 30 minute mark. ??? It may be well worth the energy cost.

Interesting. Any idea how much benefit you might expect? How would you power your heater?

You have indirectly pointed out something I have misunderstood. It is very noticeable that in the winter months, the battery charges into the green much faster. I've been assuming that to indicate the same charge capacity as in warmer months. I see now that I was wrong. Obviously the battery holds less total charge when cold, just like most other batteries.

Hello from Japan,
This is the first introduction on PriusChat forum which Japanese Prius drivers used since 2006.

Do you think we could improve our winter mileage to keep the engine coolant temperature higher than normal?
Do you think it is better to keep the engine room temperature higher than normal?
Have you ever felt the Prius engine is easy to be cooled down because of the engine-off coasting?

If you answered yes on one of these questions, you'll be a good candidate for the following modification.

The standard coolant thermostat opens at 82C(180F) and we see the nominal 88C(190F) coolant temperature after complete warming up.
There is a higher temperature thermostat which opens at 88C(190F) on the market and the nominal coolant temperature can be seen 6C(10F) higher than normal.
CAR-FLAP Thermostat WV56TA-88? - Yahoo! shopping
(Please note this internet shop is for Japanese customer only.)

edit: note that the gasket also needs to be replaced at same time.

Please refer to the attached chart for the coolant temperature graph.
The sky blue line is for the normal thermostat at 17C(63F) ambient temperature and the other lines are 88C thermostat used.

We see a few percent mileage improvement, but no ill effects can be seen even in hot summer for these two years.
Please install it at your own risk.

Enjoy your winter driving.
Ken@Japan

Thank you for this interesting idea and the supporting graph Ken!

For English speakers: I can't read Japanese, but I know a few characters. I believe the various lines on the graph are labeled something like:

Dark blue: Outside air temperature 4-6 centigrade, cloudy weather with snow
Green: Outside air temperature 10-13 centigrade, clear sky
Purple: Outside air temperature 6-7 centigrade, rain
Turquise: Outside air temperature 17 centigrade, clear sky, standard "samo"

"Samo" is written phonetically in way used for foreign words; I'm guessing there's no Japanese word for "thermostat", and this is more-or-less the sound of the English word (or the first two syllables, anyway).

The x-axis is labeled something like "time interval axis". I don't think the units have been specified. Y-axis is labeled water temperature.

The idea is interesting.

Supply might be an issue.

Your translation is perfect!
Yes, "samo" means "thermostat".

The x-axis unit is "0.1 second", and the graph is based on his 50 minues commuting.
The graph tells us he needs 1,200 seconds(20 minutes) to reach the complete warming-up temperature.
Please note that he used the EBH and he never truned on the A/C or heater.
He reported he won't see above 80C(176F) for his entire commuting if he turned on the heater(A/C).

Ken@Japan

Hope sigmaauto.com or japanparts.com will help you to supply the thermostat and the gasket.

Ken@Japan

Once again, what is the point? If you are installing electric block preheaters, if you pay 50 cents to heat the block up with electricity from your home, or if you do not have a preheater and have to pay 50 cents of gasoline to heat up the engine the same way--what is the rational for the extra personal effort and installation cost? You are not making ANY engineering sense here!

Ironically, you are not making any engineering sense.

The engine's temperature will depend on the quantity of energy used to heat it (wether it's Joules, kWh, etc). The ratio between cost and energy is quite different between electricity and fuel.

This chart will give you an idea of various forms of fuel and energy density
Image:Energy Density.PNG - Wikipedia, the free encyclopedia
Gasoline technically contains around 34.2 MJ/L. Over here one liter costs 0.80CAD (0.64 USD). If around 25-35% is converted into mechanical energy, most of the rest is heat, but a lot of the heat is exhausted. I lack the data to calculate how much of the heat ends up heating the engine block... if you figure that part out, you can start making thermodynamics engineering sense.

Dollars are irrelevant in the thermodynamics equations, they are solely used in economic analysis. I have books full of thermodynamic equations, and none of them have an equation with dollars in it.

34.2 MJ is about equal to 9.5 kWh by the way. I recall seeing that most EV cars get about 3-5 miles per kWh.

Now on top of the thermodynamic and economic analysis, there is (as mentioned in the preceding posts) an overall objective to minize fossil fuel consumption.

There is also the comfort factor. In cold winters, an electrically pre-heated engine block will start heating the passenger cabin earlier than an engine that wasn't pre-heated.

A warmer engine will also enable the more fuel-efficient hybrid modes of the Prius, where the engine shuts down when idling or coasting for example.

FYI,
The 88C thermostat is now on eBay.
eBay Motors: Prius 2001-2009, 88C thermostat and gasket (item 120369254945 end time Feb-05-09 06:26:14 PST)

Ken@Japan

Warm engines wear less so last longer.
A great way to improve you winter mileage and your quality of life is to move to a warmer climate.

On the other hand, car batteries that get too cold, won't start. At 27 below (before wind chill) where I grew up in Illinois, the only cars moving that winter morning were those with garages. It was a very cold walk to work.

Why stress out all those batteries!!!:fear:I plan to buy a battery warmer and mud flaps for the Pruis we just bought yesterday. I don't want my batteries to have a long, stress free future.

the Artist