Car cold: Driving tips for short distances especially when its cold outside

Even though the mileage doesn't show it, remember that any 'traditional' vehicle will be running choked (full rich) during this period and using much more fuel than you.

 

^ And the Prius doesn't??

 

Pretty much.

I translate this data into two other rules of thumb, that mostly apply to city driving:

1. Try to not run the ICE above idle for the first 3-4 minutes
2. Run the ICE at around 1500 rpm continuously from 3-4 minutes until ICE temp will allow glide

ICE = the petrol engine

Two rationales are behind the rules:

1. High RPM on a cold engine are *really* inefficient
2. The sooner the car can glide the better

These two objectives are at odds some of the time as the rules demonstrate, so I pick the overall best fuel economy performance for the different stages of the drive.

 

Amazing how fast the ICE heats up, even without a block heater (although I agree that a block heater is a fancy advantage if you have it.) My Honda Fit ICE warms up some 70F the first mile of driving out of the neighborhood.

One more advantage of cars with small, light engines.

 

I agree that the following which has already been identified in previous posting - that
these strategies will help a Prius' MPG in the winter for trips under 3 mph:

1) minimize the use of the heater ( dress warmly) -
2) minimize the use of the defroster ( by scraping off the ice from the windshield, treating the windshield with a anti fog chemical)
3) use a engine block heater to warm up your car ( 15 minutes t o 45 minutes using a 400w Toyota EBH).
4) grill blocking helps the Prius retain heat... some like the hobbit have tried adding insulation inside the engine compartment too.
5) keep your tire pressure up (or over inflate your tire by 7 psi) will help a Prius coast/glide regardless of the driving temperature. Portable tire air compressors that use 12vdc will more than likely blow the Prius's power adapter fuse. The rubber tubing using in hand operated tire pumps will likely crack and break in temperatures below freezing.
6) drive at a low speed (under 25 mph) while the car is warming up (for the first 5 minutes after a cold start)
7) glide/coast as soon as you can ( in Neutral if it is legal).
8) do short trips in close succession

9) When the outside temperature falls below freezing and there is a risk that my Prius might get stuck in a traffic jam I set my throttle to PWR mode to use the ICE more - to keep the ICE warm..
10) if the Prius is going to sit still for longer than 15 minutes in a traffic jam in driving temperatures below freezing - you can save gas by turning the Prius off for 15 minutes or longer and restarting the Prius when you start moving again or when you have to reheat the cabin to avoid freezing to death.

 

Honestly, I think I would just walk

 

Walter, are you using the block heater? That time is really short. In my experience, 1 hour is the minimum, and you'll know you've "undercooked" it. Two hours is better.

 

Wednesday morning, I started the car, turned the heater low, and started a stop watch. The initial coolant temperature was 3C so I knew it would take 10 minutes. Back in the house, I made a double espresso; got dressed for work, and; was in the car when at 9:25.53, the engine auto-stopped. The windshield frost was melted in the center and the wipers easily took care of it.

	Initial temp C	temp F	delay to 40C	delay to 55C	fuel (0.3 gal/hr)	fuel ($4/gal)
1	29.0	84.2	01:00.0	07:00.0	0.035	$0.14
2	23.4	74.0	01:30.0	07:30.0	0.038	$0.15
3	17.7	63.9	02:00.0	08:00.0	0.040	$0.16
4	12.1	53.7	02:30.0	08:30.0	0.043	$0.17
5	6.4	43.5	03:00.0	09:00.0	0.045	$0.18
6	0.8	33.4	03:30.0	09:30.0	0.048	$0.19
7	-4.9	23.2	04:00.0	10:00.0	0.050	$0.20
8	-10.6	13.0	04:30.0	10:30.0	0.053	$0.21
9	-16.2	2.8	05:00.0	11:00.0	0.055	$0.22
10	-21.9	-7.3	05:30.0	11:30.0	0.058	$0.23
11	-27.5	-17.5	06:00.0	12:00.0	0.060	$0.24

Within the set of data we have, 50 C hot and 6 C cold, an engine-OFF, cooling rate measures 1.8 C/min. However, heat loss is not a linear function of the temperature difference so the rate should increase with the temperature difference.

We see about an 8-10 C decrease until the engine auto-starts to reach the hot, engine-OFF temperature. If it is cold enough (not in Huntsville AL,) there should be a lower temperature where the engine generated heat should equal the heat loss. But this is an experiment for our Yankee and Snowbird members.

Bob Wilson

 

Living in N. Alabama, it will have to wait for another cold spell. It is 50+ F at 11AM, sunny and no wind.

Bob Wilson