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Block and transaxle heaters: 53.4 MPG @ 32F (0C)

  #1  
Old 12-17-2007, 11:15 AM
bwilson4web's Avatar
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Location: Huntsville, AL
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Wink Block and transaxle heaters: 53.4 MPG @ 32F (0C)

Hi,

We had a strong cold front come through yesterday and over night, the temperatures dropped to 25F (-4C). So at midnight, I plugged in my block and pan heaters so this morning, the ICE started at 34C, MG1 at 31C and MG2 at 28C.

I followed my standard warm-up cycle, speed <= 25 mph until coolant reached 70C and then trigger an ICE auto-stop as soon as possible. Thereafter, normal commuting speeds up to 55 mph and holding 25-30 mph on the last mile to work. When I parked, the MFD showed 53.4 MPG, pretty much what I get in the spring, summer and fall.

Bob Wilson
 
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Old 12-17-2007, 02:29 PM
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Default Re: Block and transaxle heaters: 53.4 MPG @ 32F (0C)

I can ( but don't ) check the MG1 temp, and MG2 temp. Is that something important to your car?

With ~3 hours of plug time in a ~25'F garage, my engine water temp said 89'F and my cylinder head temp. said 111'F. My plug-in warmer includes a high voltage battery heater, and my HV battery was 59'F this A.M.

I have 1 mile of residential, followed by 8 miles of highway ( 55 MPH ) followed by half a mile of work driveway ( usually EV ).

It was 15'F outside, and I had 34.1 MPG in my FEH after 9.9 miles.
That would have been high 20's without the plug-in heaters.
-John
 
  #3  
Old 12-17-2007, 02:39 PM
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Default Re: Block and transaxle heaters: 53.4 MPG @ 32F (0C)

Originally Posted by gpsman1 View Post
I can ( but don't ) check the MG1 temp, and MG2 temp. Is that something important to your car?
There is a UT Battelle report about the effects of temperature on transaxle energy loss that showed a significant effect at lower temperatures. In fact, one of the enhancements of the NHW20 model over the NHW11 was an improved "low friction" transaxle oil. So warming it up moves the oil into a lower friction range and minimizes how much heat has to be added to overcome the thermal mass.

This winter, I plan to do more studies and quantify the effect of transaxle preheating. The problem is all of the transaxle heating comes from mechanical working of the oil and MG1/MG2 resistance losses. I'm out to minimize the mechanical working loss.

Originally Posted by gpsman1 View Post
With ~3 hours of plug time in a ~25'F garage, my engine water temp said 89'F and my cylinder head temp. said 111'F. My plug-in warmer includes a high voltage battery heater, and my HV battery was 59'F this A.M.
I haven't considered heating the battery yet but that too should have a beneficial effect.

Originally Posted by gpsman1 View Post
I have 1 mile of residential, followed by 8 miles of highway ( 55 miles per hour ) followed by half a mile of work driveway ( usually EV ).

It was 15'F outside, and I had 34.1 MPG in my FEH after 9.9 miles.
That would have been high 20's without the plug-in heaters.
Your route sounds similar to mine and the numbers are pretty close. My 34C was 93F at the coolant sensor on the cylinder head. As soon as the ICE starts, there is about a 3-4C drop but the engine heat soon brings that back up with less than a minute.

Bob Wilson
 
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