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Newbish car questions...

post #1 of 4
Thread Starter 
I just have two questions relating to cars that have been bugging me for quite a while and have not found the answer to...

What is Overdrive? What does it do... never understood that...

And, if you are driving an automatic car, should you, or is it beneficial to put the car into neutral at stops like manual cars?
post #2 of 4

Re: Newbish car questions...

Quote:
Originally posted by chych
I just have two questions relating to cars that have been bugging me for quite a while and have not found the answer to...

What is Overdrive? What does it do... never understood that...

And, if you are driving an automatic car, should you, or is it beneficial to put the car into neutral at stops like manual cars?
No, there's no need to put automatics into neutral when at a stop light. Automatic transmissions use a viscous fluid between the transmission and engine; they don't make actual physical contact until the car is above 35-45 miles/hour or so. Therefore all that's happening when you're stopped is that the plate is spinning in some fluid, and the brakes are preventing the car from rolling forward. When you let off of the brakes, and press the gas, the engine spins the plate faster in the viscous fluid, and this causes the transmission to turn, moving the wheels to propel the car. At around 45 MPH, the plates lock together completely, which results in slightly better fuel efficiency, since the engine is now directly coupled to the transmission. You wouldn't want to do this at low speed because stopping the car would cause the engine to stall.

Overdrive is a higher gear that the transmission can be put into. So if you had a three speed tranny, and it also had overdrive, it's really a 4 speed. Overdrive was first introduced simply as a fuel-saving measure; you can travel on the highway at a given speed (say, 55 MPH) with the engine turning 2000 RPMs in OD, but in 3rd gear it might be turning 2500 RPM, using more fuel. Overdrive is a "tacked-on" 4th gear, -- a higher gear than 3rd (D) but D is at the same gear ratio that it would have been if the car didn't have overdrive. A true 4 speed transmission is going to have different gear ratios, more evenly spread.
post #3 of 4
Just put it in P (park) when you're at a red light if you don't feel like holding your foot on the brake. You can put it on neutral of you are on flat ground to save a small amount of gas if you do a lot of stop-wait-5mins-and-go (has to do with engine RPMs, higher rpm = use more gas). OverDrive just means it's a higher gear ratio of 1:1 or higher. I don't see why you would want to turn it off, I use 5th gear going 50mph and up (saves a lot of gas).

I personally hate driving automatics.
post #4 of 4
Thread Starter 
I see, thanks for the explanations
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