Important Breakthru In Fuel Efficiency! - Page 2 - Toyota Yaris Forums

10 Francis · 05-22-2013, 10:34 PM

The reason the A/C runs when you turn the defrost on is to dehydrate the air you're blasting at the inside of the windshield. It makes the defroster more effective.
The reason the Prius engineers went to the lengths of putting the thermos bottle in was because the engine doesn't run all the time, and running the PTC (Positive Temperature Coefficient) heater (an electric coil like on a space heater) uses quite a bit of current, and in that car, that reduces the electric-only driving range.

bronsin · 05-23-2013, 06:09 AM

Huh interesting.

Seeing this thread come up reminded me I havnt posted my findings.

Normally the cool engine light goes out on a typical winter morning after about a mile. With the block heater on for about 1 1/2 hours the light goes out after 4 tenths of a mile. Lower temps result in longer CEL outages and higher temps result in shorter one.

I figure on an average night in NJ using the block heater results in a 2 mpg gain. Thats for my situation which involves a short drive of ~6.5 miles. Longer drives the result would probably be less....

05-23-2013, 06:09 AM	#20
bronsin Drives: 2009 Base Hatch 2 Dr Auto Join Date: Dec 2008 Location: nj Posts: 4,790	Huh interesting. Seeing this thread come up reminded me I havnt posted my findings. Normally the cool engine light goes out on a typical winter morning after about a mile. With the block heater on for about 1 1/2 hours the light goes out after 4 tenths of a mile. Lower temps result in longer CEL outages and higher temps result in shorter one. I figure on an average night in NJ using the block heater results in a 2 mpg gain. Thats for my situation which involves a short drive of ~6.5 miles. Longer drives the result would probably be less.... __________________ Synthetic Oil: Its All In Your Head

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05-22-2013, 10:34 PM	#19
10 Francis Drives: 2010 Yaris S HB Join Date: Nov 2011 Location: Texas Posts: 33	The reason the A/C runs when you turn the defrost on is to dehydrate the air you're blasting at the inside of the windshield. It makes the defroster more effective. The reason the Prius engineers went to the lengths of putting the thermos bottle in was because the engine doesn't run all the time, and running the PTC (Positive Temperature Coefficient) heater (an electric coil like on a space heater) uses quite a bit of current, and in that car, that reduces the electric-only driving range.