Driving Style and Autobox Wear

[Hibbo]

Hibbo, the revs drop these days,they do not speed up in D. I did say at the beginning of this thread the the 124 were the last of the car with an idle relay that speeded the engine up by 50 rpm, with Motronic it was done away with

Fair enough Malcolm, I knew I should've stuck with talking about old fashioned diesels!

 

[Glenn Smith]

Yes.

The ONLY Merc engine EVER that used a DPA was the om604 used in the C220D (and it was a delicate Lucas/CAV one at that!).

As far as I'm aware, given that the revs on my cars DO drop when I select D, there is NO load sensing idle governor, so rack at idle, fuel consumption is directly related to RPM. Lower RPM due to increased load = less fuel being burnt!

Fuel consumption is not directly related to RPM, all vehicles are different and work in different ways, but a modern diesel engine will increase its fuel depending upon load, so more load at idle means more fuel being used, the drop in rpm may compensate a little, i have a c230k the revs drop to 600rpm in D, but the car does have idle speed control but this can only compensate for a certain load a gearbox in D takes a fair amount of power to turn and fuel consumption will be higher.

 

[Glenn Smith]

How many people here, with manual gearboxes, hold the clutch down while the starter is turning the engine, to save wear?

Not many I bet. And yet, people still get uppity about staying in D while parked, thinking that its costing them money, or something is being worn.

What next, are people going to start talking about magnets on fuel lines?

Just leave the damn thing in D, unless you're in a traffic jam and not going anywhere for ages - in which case turn the engine off.

Always hold the clutch down whilst starting, one for safety and mainly for putting less load whilst starting, never had to buy a starter motor yet for one of my cars! I have to say each to their own but a car will use more fuel in D rather than N whilst stationary. i tend to move into N if stopped for more than a few seconds, say at traffic lights but sometimes i don't if i'm being lazy or are on a hill. I think you'll find most handbooks recomend to move to N and pull park brake as it is considered the "correct" thing to do on a driving test and reduces fuel consumption and keeps gearbox cooler.

 

[Socrates]

The issue, which started the thread, was whether to change to N during significant waiting periods. Now, on the one hand we might say that what constitutes significant is going to be subjective: lets say waiting to pass a parked car is not, waiting at a level crossing probably is. The owners manual says change to neutral. However, there is a way of removing this subjectivity. There is one imutable process that is at work in this situation, that is, while the car is held stationary on the brakes, the energy produced by the engine, which would normally propell the car at say 5mph, has to go somewhere (law of conservation of energy). Where it goes is into the fluid in the torque converter, which gets hot. thus the question is: how hot should you allow the torque converter fluid to get, then you will get a definitive answer concerning how long to leave it in drive. QED

 

[television]

The issue, which started the thread, was whether to change to N during significant waiting periods. Now, on the one hand we might say that what constitutes significant is going to be subjective: lets say waiting to pass a parked car is not, waiting at a level crossing probably is. The owners manual says change to neutral. However, there is a way of removing this subjectivity. There is one imutable process that is at work in this situation, that is, while the car is held stationary on the brakes, the energy produced by the engine, which would normally propell the car at say 5mph, has to go somewhere (law of conservation of energy). Where it goes is into the fluid in the torque converter, which gets hot. thus the question is: how hot should you allow the torque converter fluid to get, then you will get a definitive answer concerning how long to leave it in drive. QED

Not all hand books tell you to put the car into N while waiting.

Cars that have the hold feature have that so that you do not have to sit with the footbrake depressed, and no mention of putting into D at anytime, as that would defat the object of the hold device

There has never been a case yet of a car over heating the gearbox in N

 

[television]

Fuel consumption is not directly related to RPM, all vehicles are different and work in different ways, but a modern diesel engine will increase its fuel depending upon load, so more load at idle means more fuel being used, the drop in rpm may compensate a little, i have a c230k the revs drop to 600rpm in D, but the car does have idle speed control but this can only compensate for a certain load a gearbox in D takes a fair amount of power to turn and fuel consumption will be higher.

Without reffering to a deffinate car,no genral assumption can be made, as the older ones the revs increased,onthe newer ones the revs decrease,lower revs also mean lower fuel, or at least balance out

 

[television]

You could put it like this, from the wear angle, now most of the points have come up

Shifting from N to D. and wear.

1 The engine tips on its mounts slightly.

2 valves open in the gearbox.

3 brake bands or disc are locked.

4 All of the slack in the U/Js and bearings on the prop shaft is taken up.

5 The pinion and crown wheel, all slack taken up.

6 Any splines or drive shafts the slack is taken up.

7 The gear shift and all switches there on, are engaged.

going to N all of the above is going to wear, and when you go back to D it all wears again


Now, anyone sitting at the lights and selects N and parking brake,is also wearing the parking brake.

If when the lights go green, he has to release the parking brake and select D all of items 1-6 will take up with a clonk, (sadly the chances are that he will be the only car going through the lights during that change, we have all seen them or had one in front)

We have all heard of cars that go clonk when going from D to R due to wear in all of the above components.

As said earlier modern cars with the "stop and hold" features never have to put the car into N when waiting, thats why they were invented.

Any talk of fuel consumption is speculation, the only way to test is on an real time analyzer and this point was not asked in the original question.

I for one would never buy are car that has been subjected to going from D to N every 5 mins, and I can tell in seconds of sitting in the car.

 

[eric242340]

How many people here, with manual gearboxes, hold the clutch down while the starter is turning the engine, to save wear?

Not many I bet. And yet, people still get uppity about staying in D while parked, thinking that its costing them money, or something is being worn.

What next, are people going to start talking about magnets on fuel lines?

Just leave the damn thing in D, unless you're in a traffic jam and not going anywhere for ages - in which case turn the engine off.

Oh and Television is quite right about the engine mounts, if you don't believe me then just open the bonnet and watch the engine as it moves from R to N to D. Then for good measure, rev it up and watch it lean over.

Well said,more wear and tear.

 

[kevinororke]

Hi, I started this thread so maybe I should try to finish it. Here's what I think I've learned:
1. Leaving the box in D very probably heats up the transmission fluid. I don't know if this is a problem or if it produces wear. I suspect the box is designed to cope with this.
2. Moving from D to N and back again results in parts moving which must result in wear. Whether this is significant or not is not clear. I suspect the box is designed to cope with this. It is designed to cope with high speed manual gear changes afterall.
3. There are quite a few driving situations when you must (to pass the driving test) disconnect the power from the transmission and brake the car by a means other than the service brake. Ie use the parking or handbrake.

So, when it is safe to do so I'll leave the box in D and use the service brake When it's not safe I'll put it in N and use the parking brake. Probably.

Kevin

 

[Hibbo]

Do what you want mate, it's your car!

 

[toby1]

Having trawled through this thread, and I must say, it's one of the good ones...

No one has mentioned the increase in time of the illumination of the brake lamps by having one's foot on the brake! :idea:

It's scandalous, I tell you!! :cry: :wink:

 

[television]

Having trawled through this thread, and I must say, it's one of the good ones...

No one has mentioned the increase in time of the illumination of the brake lamps by having one's foot on the brake! :idea:

It's scandalous, I tell you!! :cry: :wink:

If I had a gun,I would shoot you

 

[Hibbo]

Ah, but incandescent bulbs tend to blow more due to on/off cycles than time used

 

[Hibbo]

But the brake lights will be drawing more current from the alternator, thus using more fuel!

 

[Hibbo]

From now on, every time I stop I will select N, apply the parking brake, select P, switch engine off, get out and walk to where I was going. Best of every world!

 

[television]

I should have subtracted the cost of the lamp, and wear on the switch from post 87, though thinking about it you still need the foot brake while in N, unless you are wearing out the parking brake

 

[television]

And if someone mentions shoe leather

 

[mlc]

If I had a gun,I would shoot you

Malcolm,

Guns are available at reaonsable prices here in South Manchester, just let me know your exact needs

 

[television]

Malcolm,

Guns are available at reaonsable prices here in South Manchester, just let me know your exact needs

Thank you for the offer Mark, sadly I could not kill a fly on purpose.

 

[Blobcat]

Thank you for the offer Mark, sadly I could not kill a fly on purpose.

Unfortunately the last couple of days I have killed quite a few flies, what if your brake lights are LEDs?