Saving gas by putting your car on neutral while coasting downhill

Here’s an interesting thing that I learned this past weekend – Apparently, its possible to save gas by putting your car on neutral (the guy who told me this was driving an automatic transmission car by the way…) while going down hill. Likewise, he also told me that you can preserve your engine by putting the gear on neutral while you are at the lights or an intersection where you have to wait for a long time (read more about that in this post). Now, since cars are technology (oh common, you know they are!) I think it’s alright for me to delve into things like manual/auto transmissions on this blog without upsetting my “subscribers”. Oh and by the way, be sure to read my thoughts on ‘cruise control’ and whether it saves gas or not.

Ok, back to my story – I was going in this car (a VW Passat, w/V6, automatic transmission) with my friend and I noticed that he would shift into neutral every time we were on a steep hill and just coast all the way down. His reason for doing so was that he claimed that it saved a lot of gas. I wasn’t really aware of whether or not this would really save some gas, so I just agreed. But sure enough, when I came home, I did some research and figured that it might actually be a BAD idea to shift into neutral with an automatic transmission (although apparently its ok to do so with a manual transmission).

The first article that caught my eye was an article on examiner.com, which talked about why using neutral while going downhill was actually bad for your car, more so than good. It claimed that it didn’t really save any gas, and instead was dangerous, and could actually harm the engine. Other websites I checked also mentioned the same thing, and some people even claimed that constant shifting back and forth while the car was in motion could actually harm the transmission.

Here’s my take on the story: I think that most people are right when they say putting your car while coasting on neutral might be a gas saver – but most likely only for a manual transmission. Not for an automatic transmission. My reason for thinking this is that if you’re using a automatic transmission:

1. When you are going downhill on a auto-transmission car – the engine doesn’t really do anything anyway because you probably wont be giving the engine any gas by pressing on the gas pedal. So there is no chance of you using up any gas in the process. Yes, engine braking is certainly a factor, but I don’t think that if you disengage the engine from the transmission it will help the car go any further (because in my opinion the force the engine puts on the transmission while going down should be minimal).

2. When you put your engine into neutral it’s still going to use gas. I not an expert or anything, but in my opinion, even if you simply keep the engine on idle while coasting down hill on neutral, it would be the same as keeping the engine idle while waiting at the lights, right? So, according to that hypothesis, the engine will still be sipping some gas while you’re going downhill, because the engine will still be ON. Now, if you’d turn off the engine on the other hand, that’d probably save some gas. But apparently doing so is illegal in the some states in the US (I’m Canadian, but I think according to my driving manual its still illegal to coast or turn off engines while driving I don’t remember… but then if I turn off the engines I won’t be able to break – which is bad… especially when the roads are covered with white stuff known as snow).

3. Shifting gears every time you go downhill is surely going to exert some stress (of course, I’m taking about a really little tiny tiny effect here) on the transmission and the ‘shifting apparatus’ (sorry, I don’t know the exact names of the parts to be precise) and might require more frequent servicing. So, shifting every time you go downhill might cause the transmission to wear down more quickly, although the car will still go on running properly for the most part.

 

If you are using a manual transmission on the other hand – you might be able to save some gas by shifting into neutral because of the lesser drive train drag on the transmission. So I guess, when you go downhill you’ll be going downhill at a higher pace, and you’ll need less acceleration to get up to speed after the downgrade in the road. But, that’s a bit too extreme – even for me. And I’m pretty sure that the gas savings (when you count the pennies I mean) are pretty negligible.

Anybody else have any other thoughts on the topic?

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