Whitey ,I don’t see the fuel cut-off feature that you mentioned in your post before you edited it. I watched it several times. I also don’t see a mention of valves being closed when you coast,can you provide a time in the video where this is mentioned (by minute)?
They fuel saving features mentioned in the video are primairly efforts to reduce pumping losses, not something that goes hand in hand with coasting with valves closed.
I moved aroud a little bit up there and also lived along the Forks of the Salmon,didn’t see a TV for 2 years,starvation was an issue in the winter.
If you’re going down a long hill, you’re going to have to use the brakes to control your speed, where if you stayed in gear the engine would be doing a lot of that work. Besides wearing out the brakes faster (the wear and tear from engine braking is negligible), you risk overheating your brakes.
If your brakes overheat, they stop working, meaning you won’t be able to stop if you need to.
That is why it is posted illegal to coast down hills in some places. (Between Bullhead and Kingman, AZ, for example.)
If it’s quiet enough, they could tell by the sounds your car is making.
Everytime this subject is brought up, there is this cadre of people who think we are talking about going down Pike’s Peak in neutral.
It only takes about a 1% grade to keep a car going 35-40 mph without power. This is what we are talking about here.
There is a mile long stretch on my way home where the grade is just steep enough to keep my car going 40 mph, this road has a 45 mph speed limit. If I was to leave my car in gear, the engine braking would quickly have me having to give it some gas to get my speed back up to 40 mph. In order to go a steady 40 mph in gear, I would have to give the engine just enough throttle to make the engine match the transmission input shaft rpm so that the engine doesn’t brake the car and it would be burning maybe 3X the fuel of an idling engine.
Once again WE ARE NOT TALKING ABOUT COASTING DOWN PIKE’S PEAK.
stephaan, I suppose I am talking about the primary cause for the repair. I am curious to know what percentage of all clutch failures you repaired were caused by failed throwout bearings and had clutch discs that could have made 25k to 40k more miles. Could you give me an estimate of that percentage?
oldschool, I may have uploaded the wrong video. Let me see if I can find the one I intended to publish.
Yeah, you should totally just save up all momentum you could possibly get from going downhill, even if that means you’re doing 120 by the time you get to the bottom of it.
Nobody in this thread ever advocated letting a car run away to unsafe speeds. You are building a strawman to attack.
Good to point out the use of a strawman. You destroyed Sonof’s post.
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.
I’m not going to bust out my sliderule, but consider that you can rotate an engine with your bare hands, and then consider how much kinetic energy a car that weighs a ton hurtling down a hill at 55 MPH has. It’s a lot-- probably many, many thousands of times what’s required to to overcome the internal friction of the car’s engine.
Judging by the posters’ observations about the MPG gauge, I’m not so sure that this fuel shutoff feature is as prevelant as I thought, but it certainly works, and considering it wouldn’t cost anything for carmakers to implement, I don’t see why they wouldn’t.
No need to bust out the slide rule just name the F.I system that does this,my text reads "On many MFI and SFI systems the computer decreases injector pulse width while the engine is decelerating to provide improved fuel economy and emissions levels. On some of these systems,the computer stops operating the injectors while the engine is decelerating IN A CERTAIN RPM RANGE. It does not say a total fuel cutoff as long as you are off the gas and coasting,the devil is in the details.
I changed the video. This is the one I had in mind.
“Everytime this subject is brought up, there is this cadre of people who think we are talking about going down Pike’s Peak in neutral.”
Please read all of the comment. As one of the cadre of fear mongers, OP’s original included “In neutral, you would max out at about 70-75 mph.” Sounds like speeding to me. My point, is, you really don’t affect what you may consider cost effective savings until speed limits in all or most examples are broached, unless you’re willing to start at speeds 10 to 15 mph less then the speed limit to begin with to avoid excessive braking.
How many of you proponents are willing to start at significantly less than the speed to make the practice “worth while” and legal. Now the terms “unsafe speed” is used instead of speed limit to give testers the freedom to determine for themselves the safety of those around them.
Sorry, the last thing any other driver wants is every other car going down hills in neutral just to maximize their perceived MPG goals.
It’s just a debate, not a realistic exercise for all and NO ONE expects or wants drivers at large, including the inexperienced to indulge in it. Driver Ed, the police, owner’s manuals and the engineers that make the cars and design the roads don’t recommend the practice yet down shifting and engine braking is. They all know that such practices result in exceeding speed limits at some point.
Now if we’re talking about a 1% grade that barely maintains speed, that’s a debate you can make…I don’t see that with other posts.
I would presume that means in the RPM range larger than idle (or larger than some hundred RPM’s over idle). What other RPM range could it possibly mean?
First off, we don’t know if 70-75 is, in fact, in excess of the posted speed limit…lots of states out west have 70+ speed limits, even on rural secondary roads. The issue if excessive speed is dangeorus is separate from if coasting is.
I used the coasting approach to good effect on a recent Pittsbrugh/State College round trip. Using tolerable variances of speed limit +/- 5mph (okay, +/- 10 on the few occasions I had a road to myself), I was able to pull 46 round-trip MPG from a Ford Contour, where I used to average low 30’s making the trip at PSL+5 the whole way. Granted, I made a few aero mods, but coasting absolutely made a difference.
Remember, one can have power in the same amount of time one could downshift the Toyota Matrix in question, so the only emergency situations where power-off would get you is if immediate acceleration is needed, but only very mild, top-gear acceleration. This seems to be a fairly rare situation: seems that when “get the hell outta Dodge” is the evasive maneuver, rapid acceleration is required.
I tended to avoid such scenarios by using a modicum of situational awareness and not coasting in crowds (or even altering speed such that I wasn’t in a crowd at the top of a hill). I honestly don’t know if the incremental risk associated with coasting was fully offset by slowing down a bit, and I don’t know that anyone else does, either.
I DO know that drivers who maximize MPG tend to operate safer vehicles than those who simply don’t care, as high-milage driving requires one to make sure a buch of systems are in good working condition (tire pressure, alignment, brakes, etc). Far too many other motorists are simply happy if they can force the car to go down the road.
As you note applicable to only a limited range of vehicles, good reasearch. I would like to find more on earlier (and potentialy used by the more vehicles) fuel cut-off systems durning a coast period.
I bet there are many F.I. vehicles in use that just go to a idle fuel setting when coasting. Like all the early CIS,TBI,and many multiport, central port and sequencial systems. When the advancements in coasting fuel cut-off came about and with which systems on what models I have no idea.I hesitate to say all or even a majority of cars in use today have this system.
I DO know that drivers who maximize MPG tend to operate safer vehicles than those who simply don’t care, as high-milage driving requires one to make sure a buch of systems are in good working condition (tire pressure, alignment, brakes, etc). Far too many other motorists are simply happy if they can force the car to go down the road.
+1, High MPG drivers are also a LOT more likely to be looking way ahead than the average driver is.
I was able to pull 46 round-trip MPG from a Ford Contour, where I used to average low 30’s
You da man!! I get 43-45 mpg out of a 5-speed Toyota Yaris routinely, although now that I can’t buy ethanol free gas anymore, 44 seems to have become the new 45mpg.
I don’t do it because I am usually thinking of what I am going to do at they end of the trip,so if you can keep it front and center that you are in neutral,no don’t even do it then.
Whitey, Why don’t you just ask me a HARD question? I couldn’t possibly give you an ACCURATE percentage because I don’t know how many clutch discs, pressure plates and t.o. bearings I’ve done. The total number for all these is north of a hundred, maybe as many as 150, plus another 20 or 25 for family/friends/ and my own rigs.
As far as primary causes and root causes this is what I’ve learned.
Clutch discs don’t fail due to failed T.O. bearings as far as I know. I can’t think of any way they could.
Clutch pressure plates do fail due to T.O. bearings though. I have seen many that the mateing surfaces were blue from excessive heat, grooves ground in the t.o. bearing as well as the the surface where it mates on the pressure plate, whether it be the 3 finger type or the diaphram type.
Many customer complaints that regarded t.o bearings was “fix that noise” that they hear comeing out of the transmission area.
The primary cause for most of the clutch “discs” that I’ve replaced has been either weak pressure plate springs not clamping the clutch disc tight enough & allowing it to slip, & crank shaft oil seal leaks, & trans mainshaft oil seal leaks soaking the disc and allowing slipage, although the pressure plates generally weren’t hurt when the slipping was caused by oil leaks.
The primary causes of pressure plate replacements has been either weak springs allowing the disc to slip, damage from throw out bearing mateing surface, and because of some “extreme” customers that must get every frickin mile out of their clutch before they spend any money I have had to replace because the friction surface had grooves ground in it from the rivets in the clutch disc. This results in resurfaceing the flywheel due to rivet damage also. I remember a few that were so bad we had to push the rigs into the shop they were slipping so bad.
I don’t know if this next part addresses your question or not but when you pull a trans. for one specific problem such as clutch slipping, noise, etc, after you see what part has failed or causing the customer complaint, you look to see what the root problem is or was, such as:
Slipping clutch: Friction disc failed… because crankshaft oil seal leaked oil on it. (must replace seal also)
Slipping clutch: Friction disc failed… because pressure plate springs weak, (replace both)
In addition if just a single component fails and is also the root problem, you still check for other worn out items, or a seal that might just be starting to leak, and might not be a problem now, but could be leaking profusely in 6 months where it could ruin your repair, or any other component that could fail in that time. The alternative to not doing this is a possible component failure in that area whether it’s connected to your repair or not, and if it fails the customer thinks it’s your fault. Hope this clears it up.