I do not drive over 45 on my way to work. Would it be better or worse on fuel economy to turn off overdrive?
Leave the overdrive engaged. The transmission will figure out when to shift into this highest gear.
In most cars, any steady speed over ~35 mph will put the transmission into overdrive, where it should be for better gas mileage and reduced engine wear. Don’t try to out-think the engineers who designed your car.
Keep it in overdrive. If it is an automatic it will select the best gear for the driving situation, and if it an manual then select the highest gear that will not lug the engine.
Thanks, that is what I figured. I was checking out the Hypermiling guy on CBS, and that question popped into my head. I am trying to drop my RPM’s, just to see the difference. I only have a 3 mile drive and have no reason to drive like a Jack Rabbit.
It is worse by an amount that you will notice.
Depending on the model car or truck, it can worsen your gas mileage, even if you don’t do over 45. My truck came with the factory towing option, and recommends turning off the overdrive when towing. However, I noticed that the transmission doesn’t just avoid the overdrive gear, but shifts completely different through all gears. With OD on, the shifts are silky smooth. With OD off, it shifts hard like an old-fashioned 3 speed. But, this is better for towing, with higher line pressure and less slipping.