Gas Mileage vs Transmission wear

For an automatic transmission vehicle is the increased MPG and gas savings resulting from coasting in neutral down hills worthwhile, or does it cause more problems than it is worth in transmission wear and tear as a result of going back and forth from drive to neutral?

It doesn’t save fuel and it is just a terrible idea from a safety standpoint. You should put the trans in a sub-overdrive gear when going down a hill to keep speed under control and prevent the brakes from overheating.

Whether or not you will save gas is a hotly debated topic here that hasn’t been resolved. However, I have to ask, if you are so concerned about saving gas, why are you driving a Lexus? Are you trying to save money on fuel or are you just trying to save fuel for other reasons? If you were that concerned about saving money on fuel, I would think you would be driving a cheaper more fuel efficient vehicle.

The answer to your question about wear and tear is that your whole drivetrain, from the engine to the wheels, takes a jolt each time you shift in and out of gear. These components, including your transmission, are made to withstand these jolts in normal use, but what you are doing (or considering) is excessive use, and could lead to premature failure. It’s really hard to measure the amount of damage being done since you never really know how much longer your transmission would have lasted if you had treated it right, but I would never do something like this to my car. I don’t have spare money for a new transmission lying around.

Now let me see…Should I attempt to save a few pennies here and there on gasoline, or should I do my best to avoid having to spend $4k on a new transmission in a few years?
I’m having a really hard time deciding!

Yes, it is potentially damaging to your VERY expensive transmission.
And, no, it will not increase your gas mileage.

Seeing how in a modern car there is no increase in MPG in the first place and all you’re doing is putting undue wear on your transmission, the answer is pretty obvious.

Does anyone else wish the “Search” link above was in a flashing red 48-point bold font?

Most modern cars coasting in gear will will use no fuel at all. Just keep it in gear and save even more fuel than putting it in neutral. The car’s computer turns off all fuel to the engine when it senses that the engine is turning over faster than idle.

What happens when something darts out in front of you and you swerve to avoid it, or try to speed up when someone is coming up behind you very fast and won’t go around?

Are those really concerns?

You can swerve in neutral just as easily as you can in gear, unless you are on a motorcycle.

If someone is tailgating me and won’t go around, I just take my foot off the gas, and that encourages them to go around. Speeding up just reinforces the tailgating behavior and adds more danger to the situation if they continue to tailgate.

In principle, I agree with you. You have more control of your car in gear. But I don’t think accelerating is the answer to either of these problems.

I was just trying to make them think a little bit. Yeah those aren’t all that great an allegory, but there’s always gonna be a problem if one can’t get the car to move when they want it to.

This won’t save you any gas (unless you have the lab capabilites of MIT to measure it)it won’t damage your transmission, it wont’ cause your brakes to overheat and it won’t lead to 15 car pileups. Lastly the issue won’t go away.