Hiya, think this'll be the last part of my grand comeback spam attack.
So, there's some things I'm wondering, about engines and driving in general.
I read in the handbook for me wife's Omega that when using engine braking the fuel is cut off. Thus although the tacho is registering, you're not burning fuel. Hers is an automatic, wondering if this principle rings true for my (far more manly) manual?
Regarding clutches: we all know how impressive my clutch control is when I'm waiting on a slope, keeping the car in place with first gear and clutch and no brake. But does this bugger up the clutch/engine?
Um... think there's more but that's all I can remember for now. Cheers dudes
The man with no car
"Close the door on your way out, and don't forget your monkey."
Nearly all fuel injected cars will stop delivering fuel on over-run when it's not needed, although there are exceptions such as the V6 406 which will waste fuel when cold to help warm the cat. Care should be taken if engine braking for extended periods as the additives in petrol serve as lubrication for the engine cylinders
As for holding the car on the clutch, don't do it when it's reasonable to use the handbrake instead as it will result in early failure of the clutch. After about a minute(shorter on steeper hills) you'll get a nasty smell, that's your clutch plate burning up. Very bad.
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
swiss wrote:Hiya, think this'll be the last part of my grand comeback spam attack.
So, there's some things I'm wondering, about engines and driving in general.
I read in the handbook for me wife's Omega that when using engine braking the fuel is cut off. Thus although the tacho is registering, you're not burning fuel. Hers is an automatic, wondering if this principle rings true for my (far more manly) manual?
Regarding clutches: we all know how impressive my clutch control is when I'm waiting on a slope, keeping the car in place with first gear and clutch and no brake. But does this bugger up the clutch/engine?
Um... think there's more but that's all I can remember for now. Cheers dudes
You do not get engine braking with an automatic.
Yes, you will wear out your clutch too early holding it on the clutch.
One thing to note about an over-running engine with fuel cut-off is that it will act like an air compressor and create more heat in the cylinders. Japanese cars tend to dump fuel in this instance to give some in-cylinder cooling via the fuel.
[/useless fact]
Cars in my care:
2021 Kia Spottage 1.6 Pez Turbo Dual Clutch Gearbox Trickery
2013 Renner Twingo - donkey work
It cuts the fuel off when the throttle's closed but the revs are still over something like 1500, which is possible on an automatic as it downshifts itself coming to a stop (or dump it down a gear as mjb suggests). As pointed out, this isn't exactly the best thing for your engine/cat but it does help keep those all-important consumption figures down in the sales brochures.
Lots of auto drivers routinely use the overrides when driving downhill. You can smell the ones that don't a mile away and see the smoke bellowing from their wheelarches on long and/or steep hills
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
mjb wrote:Lots of auto drivers routinely use the overrides when driving downhill. You can smell the ones that don't a mile away and see the smoke bellowing from their wheelarches on long and/or steep hills
What's wrong with coasting downhill in 'D' ?
Cars in my care:
2021 Kia Spottage 1.6 Pez Turbo Dual Clutch Gearbox Trickery
2013 Renner Twingo - donkey work
Y'know, her indoors is a Merry Can and is thus far happier with her automatic, but after driving it for a few days until I could be arsed to sort out me coolant issue... my God, the manual is so much more fun. And, in an inverse-logic way, easier to drive.
*hugs 406*
The man with no car
"Close the door on your way out, and don't forget your monkey."
Welton wrote:What's wrong with coasting downhill in 'D' ?
The only way to control your speed is with the brake, and if the hill's long/steep/twisty enough you'll end up with flames coming from your wheelarches and an inability to stop because your pads have melted
The best example is the hill between Kemble airstrip and the M5 northbound. After airshows you can often see several cars stopped in the runaway lane with smoke pouring from them and a right stench in the air. The "ENGAGE LOW GEAR NOW" sign is there for a bloody good reason
<steve_earwig> I think this forum is more about keeping our cars going with minimal outlay than giving our cars more reason to go bang
MMMmm - yes the fuel does virtually cut off on overrun with both manuals and automatics. When there is no throttle open there is a high vacuum in the manifold this means little air to compress in the cylinder so no possibility of heating up through compression and it is this vacuum that gives the brake effect, on diesels where there is no vacuum a butterfly is fitted in the exhaust ( on trucks) which acts as a compressor to make up for that. Petrol contains no lubrication in the vapour, which is what it is by the time it gets into the cylinders, so there is no benefit lost here. Automatics use a torque converter instead of a plate clutch and this has a free wheeling component on the stator which reduces some of the reverse drive element of a fluid coupling otherwise it would generate as much braking as driving but there is a proportion of braking still available just as MJB pointed out -it can be utilised when shifted down. On larger cars and trucks a plate is fitted to automatics to lock up the coupling thus saving slippage in both drive and braking once it is rolling and between shifting. It is bad practice to ride the clutch instead of using the hand brake and you will shorten the clutch and thrust bearing life considerably. Automatics have the benefit of holding the vehicle on an incline without using the handbrake and with no detriment to the Torque Converter. ( A three or more stage torque converter is more advanced than a fluid coupling since it does what it says - multiplies the torque by a huge margin to aid setting off and fuel efficiency) Automatics are a real benefit for handicapped people and when used in high powered units where there might not be enough longevity in a plate driven clutch.
Before anyone jumps in about fuel mixture/additives in petrol engines, there is a cooling effect on the flame front using a richer mixture in normal use but this has nothing to do with the issue here with overrun temperatures since nothing is being injected and there is negligible compression to cause a heating up problem. A diesel would have full compression but even this is has to be blocked by an exhaust braking valve to be useful and cannot not lead to overheating - to my knowledge only used on trucks.
