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Discussion Starter · #1 ·
I drive 12 miles to work. Same route home again.
Workbound journey, typically about 1-2 deg C air temp at 0700 in the morning.
Homebound, about 12-14 deg C at about 1730.

Economy to work: 36-38 mpg
Economy to home 46-50 mpg

This is on days that I'm not driving anywhere during the day, so car sits idle from arrival at work to home time. Same route, same driving style, no significant difference in elevation at each end (neither way is uphill relative to the other), so why the difference?
Both starts are withg a "cold" engine - long enough to cool completely to ambient temp.

Only thing I can see is the air temp.
Does this mean I can look forward to far better economy in summer? And if so why?
 

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In a word- yes. I've also noticed over several years that my Jaguar (2.5 litre V6 4WD automatic thirsty sod) gives me 2-3 mpg (average) better fuel economy in warmer weather. I can't quote the science but internal combustion engines are definitely more fuel-efficient at higher temperatures.
 

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Diesel engines are most economical when the engine is upto running temp. Cold air temp means the engine takes longer to warm up therefore the engine is most economical for a shorter time when cold.
 

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terrain can make a difference too - I used to live in the (low) hills outside of Brussels - going in to work in brussels (downhill) I could beat the return journey by 5 MPG in the winter and 10 MPG in the summer



Edited by: smoothound54
 

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Now, if only you could have found a downhill route home from Brussels you would have saved even more...
 
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