Drive faster, get better fuel economy?

[mackguy]

Interesting observation I'm wondering if anyone else has noticed.

As we all know the CX-9 isn't exactly an economy vehicle, but I drive a lot so always trying new tricks etc to maximize fuel economy. 2011 AWD Touring... Daily I drive 33 miles to/from work (66 mile round trip), 27 miles of that is 4-lane freeway.

I tried doing all the traditional tips to maximize fuel economy, i.e. pretend there was an egg between my foot and gas pedal, accelerate painfully slow, even use manumatic to try to upshift sooner etc... drove about 60mph on the highway, vs the 70-75mph speed of traffic. Overall average was in the 17mpg range.

Got so frustrated driving like that and still getting poor fuel economy that I gave up and started driving harder... foot to the floor acceleration on the non-highway sections, and keeping up with the faster traffic... now my average is closer to 19-20mpg. It seems like on the highway the torque converter may not even be locked up at 65mph, as there's only about 100rpm difference between 65-75mph.... also at 65 it will downshift to go uphill where it will maintain rpm at higher speeds.

Another interesting note... on a long highway trip I started with Shell 87 octane... computer average was 21+mpg for the first half of the trip... when we stopped for fuel, for fun, I put in Shell V-Power (93 octane), and reset the computer... averaged 24+ for the remainder. Seems that it likes the good stuff...

 

[ceric]

Slow acceleration does not save fuel.
It actually is worse. The correct way is what they call, "brisk acceleration" to the speed you want and maintain it.
This basically means accelerate like other people do, not faster nor slower.

You have an AWD, so do not expect good MPG like the FWD.
On CX9, the drive shaft is always spinning even when the rear wheels get no torque. It is how it was designed to react quickly.
This causes energy loss. I have been getting 16mpg on mixed driving.

Check also tire pressure (> 36psi), and air filter.

 

[mackguy]

Slow acceleration does not save fuel.
It actually is worse. The correct way is what they call, "brisk acceleration" to the speed you want and maintain it.
This basically means accelerate like other people do, not faster nor slower.

You have an AWD, so do not expect good MPG like the FWD.
On CX9, the drive shaft is always spinning even when the rear wheels get no torque. It is how it was designed to react quickly.
This causes energy loss. I have been getting 16mpg on mixed driving.

Check also tire pressure (> 36psi), and air filter.

I keep the tires just under 40psi... probably is ready to have the filter cleaned..

My father in law is trying to convince me that there's no way my driving style saves fuel... he follows the little old lady approach (accelerate as slowly as possible, never drive over 60mph, even on 70mph limit highways). I was just curious if other people noticed that fuel economy improves with normal/spirited driving.

It makes perfect sense in these non DI cars... at anything less than wide open throttle you have pumping losses, so the engine is most efficient at WOT, low RPM.. if you drive along barely cracking the throttle then you're always trying to overcome that pumping loss... of course there's also diminishing returns since more acceleration requires more power which generally means more fuel but anyway, I digress (yes I'm an automotive engineer so digressions are normal)