How can you know that? We have two cars with MPG computers and you can see that the mpg meter moves faster (99 max on one, 70 max on the other) to max when I coast downhill in neutral compared to removing my foot from the gas pedal. There is no fuel shutoff while coasting with our cars as far as I can see with the MPG readout.
That said, coasting downhill in neutral might save you enough money in a month to buy a medium size candy bar.
To help my google search does anybody know the name of any manufactures technology that has this cut-off feature? Please be specfic.
I must prove it to my self that ALL fuel is cut-off, I suspect internal engine friction whould cause too much loss in speed but my mind is completly open to read up on this.
Many posters here seem to assume that the coasting would be done on steep declines, in which case I agree would be dangerous. But for grades less than 5%, the issue can be debated.
I tested a hill: a 1.5-mile 4% grade on a highway (65mph speed limit) near my house. Results: I maintained a speed of 60mph in gear, and 70mph in neutral and traveled about 0.4 mile farther.
Conclusions: In gear, no fuel consumption for 1.5 miles and no clutch wear, but was not keeping up with traffic for 1.5 miles and had to run the engine at 2,800 rpm for 0.4 mile. In neutral, continuous fuel consumption at 800 rpm (idle) for 1.9 miles, engage/disengage the clutch twice, kept up with traffic. Assuming linearity, 2,800 rpms at 0.4 mile is equivalent to 1.4 miles at 800 rpms. If engaging/disengaging the clutch twice costs 0.5 mpg in wear (or 3 to 5 cents), then it’s a wash.
Let’s not forget brakes – one of the big advantages of a manual transmission in the first place is being able to compression-coast down long grades. For a 2-mile downhill this as much of an issue, but on a reasonably shallow 14-mile grade in OR I got caught once in front of a minivan (automatic, I’m assuming) who’d ridden his brakes until they started to fade – by the time we got to an emergency turn-off we were going about 75 mph down this twisty mountain highway, which I was handling OK in my nimble Audi, but which I’m amazed this guy pulled off without going off the side of the mountain.
You can downshift with automatics too.
Oregon? You ever coast down off the Siskious, Wolf Creek Pass, Sexton Mountain, or Mt. Ashland in the south end of the state. Interstate 5 runs right through all of them. There’s some fuel saveings to be had there!!
Okay, oldshcool, let’s try it this way:
meanjoe75fan, other than VWs, has anyone ever seen an otherwise healthy clutch with a worn out throwout bearing?
Every engine that has variable timing features a “zero fuel” cam setting. Look at Honda’s 2005 VETC engine as an example:
The i-DSI1 engine’s special combustion characteristics result in leaner burning, while VTEC variable valve control technology employed in the VTEC Cylinder Cut-off System contributes substantially to electrical power regeneration (battery charging) during deceleration. Both these features help boost fuel economy. *
Those late 80’s Rangers with the hydraulic line to the throwout bearing leaked,some other models with low level noise issues.
Ahh, but your fuel use and RPMs are not necessarily proportional. If your engine has variable timing, RPMs and fuel use vary depending on specific settings.
With a VTEC engine, the valves close when you coast, but your RPMs don’t go to zero. How is an engine capable of using fuel while its valves are closed?
Edit: I have uploaded the video I had in mind. It is a hybrid engine that uses three stage variable timing, so I guess this might only apply to three stage VTEC engines, and not two stage VTEC engines.
I don’t think fuel shutoff for fuel injected engines happens at the valves. I think it happens at the fuel injectors.
Happy Camp (Siskisou County) in the 60’s now that was a special time.
oldschool, I don’t think a leaking hydraulic line and a worn out throwout bearing are the same thing, and low level noises don’t necessarily constitute failure.
oldschool, will you please stop changing the subject? I would like a direct answer to my direct question.
Has anyone besides oldschool ever seen an otherwise healthy clutch with a worn out throwout bearing?
If you read my post, gas consumption = 0 while coasting in gear.
One of the major problems with coasting in N is that if you need to suddenly accelerate the car then you have to put it back in gear prior to pushing on the throttle which could be a huge risk. Also, your foot is completely off the throttle either way so why take the risk.
centerfield9, if you look at how this site indents replies, you will see I wasn’t replying to you. I was responding to stephaan, who claims you can save fuel by coasting in neutral.
LOL I don't think Happy Camp has changed since you were there in the 60's. They might have a few computers now..... maybe 1 or 2 ........ nope, just checked, none yet :-)Whitey; Are you talking about a healthy clutch disc or healthy clutch pressure plates?
I’ve replaced several t.o. bearings (for extreme noise, squeeling or grinding) The springs in the pressure plates were below factory specs as far as pressure and needed replaced also. But the clutch discs could have made 25k to 40k more miles (depending on driver) This prompted the district service rep/eng to determine this was caused by a lot of sitting at stop lights and stop signs with the clutch in, causing wear on the t o bearings and pressure plate springs, but the discs looked none the worse for wear. This diagnosis made sense because where we lived/worked was nothing but stop signs, stop lights and stop and go driveing for miles.
Whitey:
I didn’t say you or centerfield9 could save fuel by coasting cuz I am not familiar with what you’re driveing. I said I can save fuel by coasting. I don’t have one of those fancy smancy fuel shut off engines. I have an '88 Chevy p u (carbuerated) I think the original question from centerfield applied to all vehicles, or at least whatever we are driveing. I never heard of the “fuel shut off f. i. engines” untill reading about them here.
woops, I just reread my first post and I did use the word you. I guess I thought all of you were driveing an old p.o.s. like me. Just disregard my posts re: coasting, unless you are driveing a carbuerated vehicle that doesn’t have any sort of “magical computerized fuel shut off system”
You are approaching about 2 miles of downhill but not too steep or curvy going 60 mph, no lights or stop signs at the bottom, in fact the road starts to ascend again. In neutral, you would max out at about 70-75 mph. Do you keep the manual transmission in gear or coast in neutral?
In this particular situation, I would coast in neutral. If this particular road had led to a full stop on the bottom, like a stop sign, then I would have left it in gear for DFCO.
The difference between getting around 300 mpg and getting infinite mpg downhill changes your average gas mileage very little. It’s the climbs that really burn the gas and the momentum you lose from engine braking really makes the next climb burn gas.
For example. Someone who gets infinite gas mileage on the downhills and gets 20 mpg on the climbs is averaging 40 mpg.
Someone who only gets 300 mpg downhill but because he entered the climb with more speed, gets 25 mpg on the climb is averaging about 46 mpg.
In all this discussion of what’s better for gas mileage etc., I hope safety and obeying speed limits doesn’t take a back seat. There are some wear and tear and increased gas consumption issues we just have to accept to be law abiding and keep our families safe; yours and mine. Good debate, but it’s only that. Every local has it’s own considerations and I don’t live in an unpopulated, speed limit non compliant area.