My Jeep Liberty shifts into 4th gear at 42mph, although the manual states it should shift at 30mph. Around town driving in 3rd gear wastes gas. The dealer claims there is nothing wrong with this. I thought the computer controls the shift points & can adjust shifting. Anyone know details of shift points?
30 mph seems awfully low for 4th gear. I suggest you allow the automatic transmission to do its thing, and not try to “out-think” it. There are multiple computers, and they may adapt to your driving style (depending upon their sophistication). I don’t think I’d want my vehicle to shift into 4th gear at 30 mph.
The actual speed is dependent on several factors, not just speed. I also think 30 is rather low. I suspect that if you could force it into forth, you would loose power and maybe even mileage.
If this is a car under warranty, try test driving another one like it. If it is different ask the dealer to explain if not, accept that it is normal.
42 mph is fine for O/D engagement. You do not want the trans to shift into O/D at 30 mph. The dealer is right.
The point of a transmission is to enable the engine to stay within its most efficient power band for most driving needs. You would probably notice a significant reduction in power in 4th at 30mph because the engine would be operating at an rpm much below its most efficient range. This translates into using more fuel to keep the Jeep going. So you would probably not see any chance in mileage (it might even get worse). You would also see a constant need for the transmission to downshift everytime you needed even moderate acceleration which ultimately would shorten its life. I think what has really happened is that the manual was printed with an error, not that the transmission is shifting wrong.