I know that in auto trannies, you are not supposed to cruise in neutral, I guess the trans is not getting lubricated and parts are still moving..at least thats what someone told me. But is this ok to do in a manual? Like downhill on a highway or whatever, is it ok to cruise in neutral?

 

It should be fine...an auto has a torque convertor spinning and pumping fluid through the tranny, and clutches, bands, valve body etc that need lubrication but the manual is just synchromesh and helical gears that use 75 or 80w90 gear oil, and doesnt have a pump.

 

I had a '82Colt and '89CorollaSR5, both stick-shift. I cruise in neutral every chance I got and as long as I could. I got 41MPG combined on the Corolla, mostly due to that technique. They both last forever. Now i'm getting 18-19MPG combined on my 5speedAuto '04SE.

 

Not only is it safe to cruise in neutral -- it is smart, because it saves gasoline plus very slightly reduces engine wear.

I cruise in neutral every chance I get. But you should never do this in any vehicle with an auto trannie -- the trannie won't get proper lubrication.

I have one recommendation if you do this with your manual trannie vehicle. There will be times when you are coasting and need to get back in gear (rather than coast to a stop). For these occasions, you should do the following:
- learn the approximate engine speed that will result when you get back in gear,
- while still in neutral and with the clutch engaged (out), take the engine to that speed,
- release the gas, step on the clutch and quickly shift into the appropriate gear,
- engage the clutch in gear and see how close you were to estimating the proper engine speed.

With just a little practice (and thought), I've become quite good at getting the engine speed very close on every shift like this. This is a form of double clutching and it is easier on the clutch, the gears and the engine than not doing this.

 

 

Silvermax, in the short time I’ve been part of the org, I’ve developed a genuine respect for your car wisdom. I write that because I have heard different perspectives on traveling in neutral. According to the experts for my previously owned 2003 VW Passat 1.8 Turbo 5MT, coasting in neutral was not optimal for mileage. As a fuel saving feature, the Passat’s computer sensed when the car decelerated in gear. When that happened, the computer delivered less fuel to the engine that it did during an idle.

The Passat had an instantaneous gas mileage setting on its computer display. When I took my foot off the gas to approached toll booths while in gear, the reading would regularly exceed 199 mpg for those few seconds. When I did the same thing in neutral, the reading would rarely exceed 150 mpg for those few seconds. (Of course I could have continued coasting for much farther, which over a very long distance may have benefited the “idle’s” mileage, but in normal driving that was not an option.) Because of the computer, the Passat got better mileage decelerating in gear than it did coasting in neutral. I’d be curious to know if the Nissan engineers incorporated the same “fuel saving” feature in our computers.

 

Yea when i had my first car a 5 speed max i did learn to always match the gears. Still do all the time its so fun driving a stick i def dont like autos lol thanks so much for the info guys

 

I see taxi drivers contantly doing this in Europe where gas prices as we know are much higher. They take off and just let it roll till next light on Neutral.

We all know they do millions of miles and if the technique wasn't safe, they wouldn't do it.

 

Thanks MDS for this compliment. But in respect to "car wisdom," I usually defer to lightonthehill (except for when he did not know how the "parking brake" on the Max actually worked -- it is a small drum brake around the rear axel with the disc outside of the drum).

I believe the European cab drivers have it correct -- coast whenever it seems to make sense. I know of no decision by Nissan engineers that would make it more economic to stay in gear rather than coast.

There are times driving when (even though you could coast) it makes safety sense to stay in gear. One would be descending a steep, winding hill where you can use engine braking to reduce the wear on your brakes while keeping your speed under better control.

But the real advantage of a manual transmission is driver knowledge and decision making. An auto trannie only gets a few parameters to decide which gear should be used (or pully setting in a CVT). But a driver can see and anticipate things that are coming -- thus making better decisions about the proper gear to use. The only problem is that some drivers have a tendency to go to sleep mentally when driving. For them an auto trannie does make sense.

 

Well, what if I put an automatic on neutral at a stop light? Is this OK?

 

The auto trannie will actaully get slightly better lubrication in neutral when the vehicle is not moving -- because the engine's RPMs will be slightly higher when the trannie is in neutral than when the trannie is stopped but still in gear.

The reason you should not coast in an auto-trannie vehicle is because the transmission is turning with the wheels (50 MPH or so) while the trannie fluid pump is idling with the engine (essentially the same RPM as you would have when the vehicle was stopped). Not good.

 

silvermax - wow you really know your stuff. lol thanks for all of the info!

now, what about if you will be coasting for a shorter period of time, and you hold the clutch in instead of taking the car out of gear. The book says not to hold in the clutch for a long time (I think)..im sure there is a reason for this. Anyone know why? is it safe?

 

SilverMax, you're the man
How do you know so much? You must be a mechanic; I have a mechanic friend of mine that would answer anything so quick!

 

The reason not to hold your clutch in (disengaged) for more than a short period of time is the throw-out bearing in the clutch. I had a 65 Corvette in my youth (25 to 35) and the throw-out bearing in the clutch (4-speed) went bad. And I did not even hold that clutch in at a stop light.

You should always wait for lights (or trains, etc) with the tranny in neutral.

No, I'm not a professional mechanic. I am a Mechanical Engineer who worked for an oil company for 35 years before retiring in 1998. Like lightonthehill, I've been around cars for many years, and just picked up pieces of information. I don't consider myself an expert on cars, but rather an expert on gasoline octane (I did work for an oil company and needed to know that information).

 

Nice...you sound a lot like my tech teacher in high school, had a degree in mechanical engineering technology and manufacturing, we'd always talk about gas mileage and I told him I'd put my automatic pontiac in neutral down big hills and your answer was exactly what he said why not to do it. Really interesting stuff.

 

Throw out bearing...what are the signs of that going bad? I know about 75% of the time my clutch squeaks when i press it in, sometimes when i let out. sometimes it wont squeak at all. That wouldnt have anything to do with that bearing, right?

 

My only experience with a bad throw-out bearing was in my 65 Corvette. When I stepped on that clutch after it went bad, there was heavier then normal resistance, and then while the pedal was going down, there was a pop of the bearing not functioning properly.

I suspect there are a number of ways that a throw-out bearing can fail. Hope others here have the knowledge to suggest if your problem could be that bearing.

 

silvermax thanks again for the info. ok so i guess its not the bearing, which is a good thing. but now i learned another thing! not to hold the clutch in unnessecarily! (<< i spelled that way wrong lol)
because sometimes i did that

 

I was thinking of another stupid question, because of our great gas prices, would this save gas?

I know you must have the answer...

 

To my knowledge,

Both auto and manual tranny fuel injected cars cut off fuel altogether when you coast and in gear.

For manual transmission, when in gear with the clutch engaged and coasting, no fuel at all is delivered to the engine. If you press the clutch in or put it in neutral, the car must idle and therefore needs fuel. During coasting and in gear however, the momentum of the car keeps the engine turning, and therefore no fuel needed.

For an auto car, as long as the torque converter stays locked up when coasting, no fuel is delivered (usually above 40-45mph or so). Once the torque converter unlocks, the engine idles and uses fuel.

So if you want to save the maximum amount of fuel on a manual transmission car, coast in gear for as long as you can... till the engine is at idle rpm, and then press the clutch in.

Joe.

 

If you have a manual trannie, it will coast much further and easier in neutral than it will, even in top (6th) gear. In gear you get engine braking and the vehicle will slow down much faster than it will when coasting in neutral. So I will continue to coast in neutral.

I also think that when the engine is turning while coasting in gear there is still some fuel sent to the engine -- it may well be less than the fuel sent to an idling engine. But it is still getting some fuel when coasting in gear.

 

What would be the purpose of delivering fuel to the engine during coasting in gear? I don't see why it's necessary, other than to burn more fuel for the gas companies. I've had an air fuel ratio meter on past cars and they never registered any fuel delivery during coasting in gear... but who knows, the engineers I guess.

It's true, the car will coast much further in neutral than in gear. I guess you have to decide depending on the situation. If you are coasting down a big hill that overpowers the engine drag, perhaps that's a good time to leave it in gear. Or if you know that you'll make it to the next red light coasting in gear, leave it in gear. If not, put it in neutral. Leaving it in gear can extend brake life too depending on the situation. The more you drive and get used to your car, eventually you just know what's the best thing to do in different situations, that's the beauty of driving manual...

There's other more important issues about coasting in neutral that outweigh the potential fuel savings. Coasting in neutral on a turn or on wet pavement can create less traction than coasting in gear. Sliding your car off the road will cost far more than any gas you save! Or you could be coasting in neutral, and the red light in front of you turns green, and you need to put it in correct gear and continue cruising. If you're not matching rpm's to your speed & gear choice, you add wear to the clutch. If you'd have just left it in gear, you may just be able to press the gas and cruise on...

Obviously with hundreds of different scenario's, I guess there really isn't a best way to do it...

Joe.

 

...How would the engine run if the fuel was cut off? Think about it.

 

The momentum of the car forces the wheels to turn, which forces the engine to turn, that's how.

Joe.

 

Uh oh...i do that all the time in my auto. guess I will stop now.

 

So you are saying the fuel is completely cut off? How is it possible your power steering works....

 

I truly doubt that the fuel is cut completely off -- otherwise the engine would be turning but not "running." Because there is no fuel in the cylinders, the spark would not be firing -- not likely. Try that by driving and then turning off the ignition (not a good idea) and then turning it back on again when you want to accelerate.

But if the engine is turning (but not running), the belts are all turning, including the belt that powers the power steering pump.

 

Yea but it isn't practical to say that the engine is off, and in neutral nothing is moving anyway. Good point.

 

Yea if there was no fuel being delvered to the engine I think it would be slowing down significantly...I rememer trying to push start a newer bimmer and after about 10MPH let the clutch out and because of the immobilizer or something, no fuel was being delivered and it just bogged down quickly and stopped again. no combustion but the engine was turning.I think thats kinda what would hapen in the no fuel situation. Just my .02. I think what silvermax said is right, there is a minimal amount of fuel being delivered to the engine on coasting..but yes the point is, cruising in gear will slightly slow you down, or prevent you from going too much faster, as coasting in neutral will not. But as far as getting back into gear, I dont always get a *perfect* rev match, but close to is better than engaging the clutch without revving at all. Anyway, when I coast a few times in neutral, than it doesnt make me feel so bad when i wanna gun it a few miles ahead.

 

The engine is still getting fuel if the car is on.... do this coasting experiment on a colder day and you will see that exhaust is stilling coming out of the tailpipes, indicating that the engine is still running and getting fuel. I know the new hybrids have a fuel cut off feature when idling and all power is then supplied by the electrical system but the Max does not have that feature.

 

I've had years of practice and still don't always get it *perfect* either. Like you say, close is better than no rev at all -- bringing the engine and parts of the trannie from idle speed (750 RPM) up to speed driven by the front wheels. I find that I don't do a trannie rev after coasting unless the final engine speed will be above about 1,100 RPM or higher. So on the low end, I'm willing to be off about 350 to 400 RPM or so. Guess that is my tolerance at all speeds -- and I'm usually closer than that.