Cruise control automatically downshifting
#1
Pole Position
Thread Starter
Cruise control automatically downshifting
Last night I had my cruise control on (set on 65) and started down a long steep hill. The hill was about three-quarters of a mile long. My IS downshifted from 6th to 4th gear to keep the speed at 65 mph. Every other vehicle I have driven and used the cruise control on has let the car coast up to whatever speed that gravity would allow or until I hit the brake. It’s not that big of a deal to me but I was paying close attention to the fuel mileage and when the car downshifted into 4th the RPMs went up to 4500 and the mileage reading immediately went downward.
Have anyone else experienced this?
Have anyone else experienced this?
#5
Super Moderator
Originally Posted by cmusic
Every other vehicle I have driven and used the cruise control on has let the car coast up to whatever speed that gravity would allow or until I hit the brake.
#6
Originally Posted by Bichon
The IS actually feels like it is downshifting, an odd sensation, but in this case I'll often see my tank mileage increase by a tenth of an MPG.
#7
Lexus Champion
Originally Posted by cmusic
It’s not that big of a deal to me but I was paying close attention to the fuel mileage and when the car downshifted into 4th the RPMs went up to 4500 and the mileage reading immediately went downward.
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#8
Pole Position
Thread Starter
I think the gas milage computations take in to account the amount of fuel going to the engine and engine RPM. At 65 mph the 250 engine is turning 2000 RPMs in 6th gear. Shift down to 4th at the same speed and the RPMs jump to 4500. More RPMs require more fuel regardless of how far down the gas pedal is pushed. I had the instrument panel display set to the average MPG screen when this happened. The display takes a reading at timed intervals and computes the average with the previous readings. It showed I was averaging 33.1 MPG before the downshift and 32.4 MPG at the bottom of the hill. I then drove on mostly flat roads for another 20 miles (at 65 MPH in 6th gear) and the average rose back up to 32.9.
I'm not too concered with it though. Although at one point in my approximately 150 mile drive last night, about 45 miles in, the display showed I was averaging 35.6 MPG!!
I'm not too concered with it though. Although at one point in my approximately 150 mile drive last night, about 45 miles in, the display showed I was averaging 35.6 MPG!!
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