Transmission wear from P&G (pulse and glide)?

[Gasoline Fumes]

Originally Posted by EcoCivic

Thanks. I don't think the hills I encounter on my daily commute are really long enough to be worth shutting the engine off for (1/2 to 3/4 mile of coasting at a time at the most), so the only EOC I normally do is shutting the engine off once I pull into my driveway and coasting into my garage.

If you track your MPG and get consistent numbers, you can easily try EOC and see how much difference it makes. 1/2 to 3/4 mile at a time sounds worth it to me. If you can estimate the total potential coasting distance with the engine off, add that distance to your miles and recalculate a tank to see the difference.

[EcoCivic]

Originally Posted by Gasoline Fumes

If you track your MPG and get consistent numbers, you can easily try EOC and see how much difference it makes. 1/2 to 3/4 mile at a time sounds worth it to me. If you can estimate the total potential coasting distance with the engine off, add that distance to your miles and recalculate a tank to see the difference.

Good point, I'd have to do some experimentation to know for sure. One calculation I did do though assuming 5 minutes per day coasting at 0.2 GPH (typical idle fuel consumption according to my Scangauge) I could save 0.016 gallons on a 25 mile trip if I shut the engine off when coasting assuming no losses from having to restart the engine.

If I'm averaging 50 MPG (close to my best), I burn 0.5 gallons of fuel. If I saved 0.016 gallon of fuel with EOC, I would have used 0.484 gallons instead and would theoretically average 51.6 MPG assuming no losses from restarting the engine. Although 1.6 MPG is a decent gain, I would assume that real world gains would be slightly less than that due to the slight losses from having to restart the engine.

But when the increase in either starter wear from using it to restart or clutch/synchronizer/drivetrain wear from constant bump starting is considered as well as probably somewhat more wear on the engine and potential safety concerns, to me that offsets the theoretically possible 2-3% savings.

[MeteorGray]

Yeah, coasting with the engine off has no appeal to me.

For the cost of a few extra pennies in fuel, the toll it would take on safety and in wear-and-tear on my car and my nerves make it a poor tradeoff, for me.

Not so for others.

Having choices is wonderful.

[SDMCF]

Originally Posted by EcoCivic

the only EOC I normally do is shutting the engine off once I pull into my driveway and coasting into my garage.

That raises another issue so let's head off on a tangent. If you drive forward into a garage (or driveway in my case) then you will have to turn the car around at the start of your next trip (when the car is cold) before you can head out again. Would it use less fuel and cause less wear on the car to turn it round when you arrive home (and reverse into the garage) so that this manouver is done when the car is at full operating temperature?

My approach to my home is down hill so I sometimes turn the engine off 100m before turning into my driveway and then roll into my parking spot. It is of course difficult to turn the car around with the engine off so I rarely do that (it involves a handbrake turn in my driveway). This means I always have to turn the car around when I leave and the car is likely to be cold. Swings and roundabouts.

[Isaac Zachary]

Originally Posted by MeteorGray

Yeah, coasting with the engine off has no appeal to me.

For the cost of a few extra pennies in fuel, the toll it would take on safety and in wear-and-tear on my car and my nerves make it a poor tradeoff, for me.

Not so for others.

Having choices is wonderful.

For me it depends on the circumstances.

Slow street? Slight grade? Small car? Nobody around? Then why not?

Long 8% grade mountain pass? Class B commercial vehicle fully loaded? Highway full of traffic?

Originally Posted by SDMCF

That raises another issue so let's head off on a tangent. If you drive forward into a garage (or driveway in my case) then you will have to turn the car around at the start of your next trip (when the car is cold) before you can head out again. Would it use less fuel and cause less wear on the car to turn it round when you arrive home (and reverse into the garage) so that this manouver is done when the car is at full operating temperature?

My approach to my home is down hill so I sometimes turn the engine off 100m before turning into my driveway and then roll into my parking spot. It is of course difficult to turn the car around with the engine off so I rarely do that (it involves a handbrake turn in my driveway). This means I always have to turn the car around when I leave and the car is likely to be cold. Swings and roundabouts.

My guess is that re-starting the car just as you reach your house would be the most efficient.

Either that or coasting backwards from the top of the hill to your driveway...

[RedDevil]

I never shifted to Neutral when I still had a manual.
I always just put my foot on the clutch and kill the engine, leaving the tranny in high gear ready to release the clutch to immediately restart the engine at any time necessary.
But I never P&G'd much, just the long roll on the exit of the freeway or towards a stop, using the last bit of speed to get it ticking over again.

[RedRyder]

Besides being stuck out of gear with no syncromesh, some of the no-coasting rules may date back to the days before hydraulic brakes, when you needed engine braking to assist your 100% mechanical stopping force.

Speaking about braking, one issue I have with engine off coasting is no vacuum to the power brake system. While I learned to drive without power assisted brakes in the previous century, today even sub-compacts have power brakes. And the amount of pedal effort these systems need to slow or stop with no vacuum is multiples of the effort in the older systems.

While I have toyed with the idea of adding an electric vacuum pump from a truck or bus to allow full assisted braking with the engine off, I would not try POC again without that mod.

I will stick to just putting the manual transmission in neutral for now. (Though the ScanGuage shows less gallons per hour fuel flow in gear than idling going down a hill, go figure.) And I always turn off the engine while waiting my turn at the bank drive-up or a flagger-controlled one-lane road construction area.

[Piotrsko]

Two comments: resize the master cylinder to a 5/8" bore and longer stroke manual brake or Summit has an electric vacuum pump kit for $200 but it needs an external relay. The summit kit is on my electric ranger for 6 years now because I want a divorced dual system

[RoadRaceJosh]

Most all production automotive manual transmissions are splash lubricated. The input shaft turns the counter shaft/cluster gear which slings oil around. The speed gears on the main shaft are de-clutched from the main/output shaft when in neutral. This means that the vehicle under tow has the main shaft spinning inside the stationary speed gears. Because all the speed gears are stationary the cluster and input gears are stationary and providing no lubrication.

The ZF S6-650 Ford used had a lube pump, but it was on the counter shaft which is of no help with the engine off.

[Isaac Zachary]

Originally Posted by RedDevil

I never shifted to Neutral when I still had a manual.
I always just put my foot on the clutch and kill the engine, leaving the tranny in high gear ready to release the clutch to immediately restart the engine at any time necessary.

Sounds like that would cause exceptional wear at the throwout bearing and pressure plate fingers.

Originally Posted by RedRyder

I will stick to just putting the manual transmission in neutral for now. (Though the ScanGuage shows less gallons per hour fuel flow in gear than idling going down a hill, go figure.)

Some engines cut fuel during "engine braking." After all, there's no need to burn fuel to slow down a vehicle. Gravity and car momentum are what keeps the engine turning.

Still, braking is braking and it's not the fuel mileage at any one moment that counts, but rather the average fuel mileage over the entire trip.

But if you need to brake anyway to keep your speed down, you're better off doing so in gear.

Originally Posted by Piotrsko

or Summit has an electric vacuum pump kit for $200 but it needs an external relay.

What about a vacuum canister reservoir and vacuum gauge? It would seem cheaper than buying a pump and in most instances the idea is to have enough braking power for an emergency as engine braking can be done with the fuel shut off anyway.