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Mileage is better when I have A/C on - huh?

J

JimKIII

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Truck has almost 10K miles now. I drive mostly freeway both flat and mountainous over Snoqualmie Pass and Blewett Pass in Wash state. Eastern Washington is mostly flat. I'm always using Chevron gas. We're now getting some pretty good heat in the mid-80s and 90s so I'm using A/C now.

I was shocked to find that I get better mileage when the A/C is on than off. Average with A/C off is ~ 14.5mpg. With A/C on and going over both passes the other day the truck averaged 16.5mpg. I couldn't believe it, so I shut the A/C off for about 40-50 miles a couple times and the mileage went back down to ~14.5; crank up the A/C and back up to ~16+. I'm cruising at a fairly steady speed between 70-75mph in both scenarios.

This unofficial experiment sure puts a wrench in my old thinking that driving with A/C really hurts MPG stats. That was true with every other rig I've owned, but not this one it seems.
 
Do you have the windows down with the AC off?
If so, its aerodynamics. With the windows down you have more drag as the air is flowing into the truck and pushing back on it.
 
Crusty old shellback said:
Do you have the windows down with the AC off?
If so, its aerodynamics. With the windows down you have more drag as the air is flowing into the truck and pushing back on it.
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Windows were up at freeway speeds. This experiment was done going back and forth across Washington state - 4hrs each way.
 
mcarey said:
Winter vs summer fuel?
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I assume all fuel was summer fuel since this was done Monday and Tuesday of this week. I filled up at a Chevron in the morning, filled up at another Chevron 250 miles away, then another one the next morning and so on until I got back home. I'll be doing another trip to eastern Washington soon and will check the whole thing out again.
 
JimKIII said:
I assume all fuel was summer fuel since this was done Monday and Tuesday of this week. I filled up at a Chevron in the morning, filled up at another Chevron 250 miles away, then another one the next morning and so on until I got back home. I'll be doing another trip to eastern Washington soon and will check the whole thing out again.
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Ah, it most definitely was. I didn't realize you were talking about back to back days.
 
You don’t mention whether you were using cruise control in post #1. Is it possible that psychologically you were more comfortable with the AC on and therefore drove in a more relaxed fashion?

Did you measure the mileage by evic, hand, or both?
 
TinGoatTravelers said:
You don’t mention whether you were using cruise control in post #1. Is it possible that psychologically you were more comfortable with the AC on and therefore drove in a more relaxed fashion?

Did you measure the mileage by evic, hand, or both?
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Never use cruise control and measured mileage by what the digital dash reads 'Ave MPG'. The A/C doesn't really cool the cab down much so there's not that much delta in ambient comfort. I don't know the digital sample rate of the dashboard fields, but the 'Avg mpg' field changed within a couple of miles of me switching A/C on and off. Switch the A/C on to max and within a couple miles the 'Avg mpg' went from 14.x to 16.x mpg. Turn of A/C and within a couple of miles the 'Avg mpg' drops back down to 14.x mpg.

BTW, what is 'evic'?
 
JimKIII said:
Never use cruise control and measured mileage by what the digital dash reads 'Ave MPG'. The A/C doesn't really cool the cab down much so there's not that much delta in ambient comfort. I don't know the digital sample rate of the dashboard fields, but the 'Avg mpg' field changed within a couple of miles of me switching A/C on and off. Switch the A/C on to max and within a couple miles the 'Avg mpg' went from 14.x to 16.x mpg. Turn of A/C and within a couple of miles the 'Avg mpg' drops back down to 14.x mpg.

BTW, what is 'evic'?
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EVIC = Electronic Vehicle Information Center. Based on your description of its behavior, I’d bet calculating old school would show no material difference. I’m not an engineer, but the way those numbers are changing on the evic sounds like voodoo magic…
 
Man you’d probably get 19.2 with the muzzy hack....
 
TinGoatTravelers said:
EVIC = Electronic Vehicle Information Center. Based on your description of its behavior, I’d bet calculating old school would show no material difference. I’m not an engineer, but the way those numbers are changing on the evic sounds like voodoo magic…
Click to expand...
You're probably right.
 
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