Using low gears in an auto

[Bobby]

Revs are about 4000 in a 2000cc engine. Not excessive I reckon.

It probably redlines at 6000+ rpm. 4000 rpm is 2/3rds the max.
The motor is warmed up, under no stress whatsoever. It is freely spinning.
That really has to be very beneficial for it.

Are you sure that you can't burn out an auto transmission doing that?
What about descending the long Adelaide Hills?
You could burn out your brakes or your transmission or both.

I am pretty sure that is good for an auto. Autos overheat by excess gear changing or slippage.
At a higher revs (only above 2000 rpm) the torque converter in the autos are in a lock up stage.
There is no slippage, it is just happily spinning.

In caravan tow sites they often say to lock it in 5th or 4th on a 6 speed auto. Overdrive gears are not suited to heavy work.
Get the auto up and spinning freely in a set gear, not laboring, changing gears and slipping a lot.
Select the gear according to the revs. Say 1600+ for a big lazy diesel, 2200+ for a petrol. For a modern turbo small diesel, maybe 2000+ ?

Certainly, do you own research. It is your car and your auto.
Generally in owners manuals it says to select a lower gear when in high traffic , snowy conditions or towing heavy loads. That sort of thing.
Noone reads it, as they all think 'Select D and drive.'

It is an interesting topic.

But to slow down you create energy.
That energy can burn out brakes or boil brake fluid
but surely it would also heat up an auto gearbox?

[sprintcyclist]

............ I am pretty sure that is good for an auto. Autos overheat by excess gear changing or slippage.
At a higher revs (only above 2000 rpm) the torque converter in the autos are in a lock up stage.
There is no slippage, it is just happily spinning.

In caravan tow sites they often say to lock it in 5th or 4th on a 6 speed auto. Overdrive gears are not suited to heavy work.
Get the auto up and spinning freely in a set gear, not laboring, changing gears and slipping a lot.
Select the gear according to the revs. Say 1600+ for a big lazy diesel, 2200+ for a petrol. For a modern turbo small diesel, maybe 2000+ ?

Certainly, do you own research. It is your car and your auto.
Generally in owners manuals it says to select a lower gear when in high traffic , snowy conditions or towing heavy loads. That sort of thing.
Noone reads it, as they all think 'Select D and drive.'

It is an interesting topic.

But to slow down you create energy.
That energy can burn out brakes or boil brake fluid
but surely it would also heat up an auto gearbox?

I never thought of that.
'Where does the dissipated energy go to ?'

........... WHAT IS ENGINE BRAKING?
As you will have gathered, we’re fans of the modern combustion engine. Not just for its sophistication but for the unbridled genius of its simplicity.

In standard petrol (gasoline) engines, engine braking works by restricting airflow (by releasing the accelerator) which causes a high manifold vacuum that the cylinders have to work against.

This has the effect of sapping energy from the engine which is what gives that sudden sense of deceleration and drop in power.

While some of the braking force is due to friction in the drive train, the majority is caused by the manifold vacuum created by the lack of air.

Check out the video below which explains engine braking in a petrol engine, followed by Jake Braking in a diesel engine.


WHY IS IT GOOD?
Engine braking, aside from being incredibly clever, has three distinct day to day benefits that could improve your driving experience.

1. IT REDUCES WEAR ON YOUR BRAKES.
Engine braking slows the car without the need to apply the brakes. Because the car is slowing passively it allows you to maintain control of the vehicle, controlling your deceleration so you only need to apply the brakes at much lower speeds for a much shorter period of time.

This means less wear, less heat and less fade.

The obvious benefit of this is your brakes will last much longer which increases value.


2. IT’S SAFER
Active use of engine braking (changing down in a lower gear) is advantageous when it is necessary to control speed while driving down very steep and long slopes.

More over, by engine braking when you see traffic slowing ahead rather than waiting until the last minute to stop you give yourself and those behind you more time to respond to changing situations.

You can maintain safe intervals simply through easing off the accelerator rather than applying brakes. Don’t forget a brake light is a warning to the person behind you causing them to brake and the person behind them and so on.

It’s not hard to understand how congestion occurs for no obvious reason.

You also have the advantage of being in a better position to react if something unexpected happens. A lower gear means you can either slow down or speed up in order to avoid an emerging hazard.

A high gear at low speeds saps power and increases the chances of a stall. Plus sudden, sharp braking makes it more likely the car behind to drive in to the back of you.

WANT TO KNOW MORE? VIEW OUR INFOGRAPHIC ON THE BENEFITS OF ENGINE BRAKING

3. IT’S BETTER FOR THE ENGINE
First of all, to dispel the myth – engine braking does not harm your engine at all. Engines are designed to run at thousands of revs per minute for hours at a time. Changing down, whilst may be a bit jerky at times, doesn’t inflict any damage.

It’s also good for the engine because it was designed to be driven that way. Whilst brakes have moved on from drum brakes (which is why engine braking was relied upon a few decades ago), the core of an engine is essentially the same.

It’s better for an engine to gradually shift down (or up) through gears rather than going from 5th to 2nd.

It’s also far more fuel efficient for the same reason. Engine braking shuts off fuel consumption, as opposed to just braking or putting the car in neutral.

You’ll also use less fuel when pulling away in a lower gear than pulling away at low speeds in high gear.

All this adds up to a safer, more economical drive on brakes that will last longer.

MAT FOUNDRY GROUP ARE A LEADING MANUFACTURER OF GREY AND DUCTILE IRON CAR COMPONENTS. TO LEARN MORE ABOUT US VIEW OUR PRODUCTS OR CONTACT US TODAY ................

https://www.matfoundrygroup.com/News%20 ... ould_do_it

[Bobby]

Yes Sprint - that's engine braking - it heats the engine and gearbox too.

[sprintcyclist]

From how I read it, during deceleration the engine is given no fuel. So it won't generate heat of it's own accord.

Also, during deceleration the motor is given no or little air intake during the intake cycle.
There is a partial vacuum inside every cylinder the piston is pulling against to complete the intake phase of the cycle.
During the compression stroke, the piston is pushing against a pressure to complete the compression phase of the cycle.

When the revs are higher, every piston is pulling against that vacuum or pressing against that pressure more frequently.


Makes me want to go and drive down a hill

[sprintcyclist]

......... The principle of braking is to convert the kinetic energy into heat energy and release it outside the vehicle. However, over a certain amount, the heat generated can not be dissipated easily and the efficiency of the brakes is affected severely. In comparison, the engine is designed to take and process a lot more heat than the braking compartment. Therefore, the heat generated by the engine braking can actually be handled by the cooling system of the engine. The cooling system of modern-day cars is very sophisticated and can take a lot more beating. It has been tested in extreme conditions over long periods of time. This is the most reliable method of heat dissipation in a vehicle. .................

https://www.carblogindia.com/what-is-en ... stem-work/

I have never seen any engine heating when I have been using engine braking.
I have done it for a long time down Mount Bunya in 2nd gear. Was never even a concern.
Engine was as cool as when idling, maybe cooler

[Bobby]

......... The principle of braking is to convert the kinetic energy into heat energy and release it outside the vehicle. However, over a certain amount, the heat generated can not be dissipated easily and the efficiency of the brakes is affected severely. In comparison, the engine is designed to take and process a lot more heat than the braking compartment. Therefore, the heat generated by the engine braking can actually be handled by the cooling system of the engine. The cooling system of modern-day cars is very sophisticated and can take a lot more beating. It has been tested in extreme conditions over long periods of time. This is the most reliable method of heat dissipation in a vehicle. .................

https://www.carblogindia.com/what-is-en ... stem-work/

I have never seen any engine heating when I have been using engine braking.
I have done it for a long time down Mount Bunya in 2nd gear. Was never even a concern.
Engine was as cool as when idling, maybe cooler

The energy is till being converted to heat inside the engine
and is being dissipated via the car's radiator.

[sprintcyclist]

........... Engine braking is the process of using the engine to slow the vehicle down instead of using the vehicle brakes. Engine braking can be used on both gas or diesel engines and is used to slow a vehicle down or control vehicle speed without using the brakes on a steep downhill grade, while also help the brakes from overheating. Engine braking transfers the heat energy to the engine instead of the brakes and releases the heat to the engine cooling system.

The gasoline engine uses engine braking by using the engine’s throttle plates. When you close the throttle plates on the engine, it can no longer pull air in large amounts and the fuel injectors shut off to cut most fuel to the engine. The cutting of fuel and closing of the throttle plates cause the engine to turn by the powertrain instead of the normal engine combustion process of the engine. This in turn will put a drag on the vehicle and slows it down without using the vehicle brakes. ...............

https://www.yourmechanic.com/question/h ... aking-work

[Valkie]

One small "hidden" issue with engine braking that is not advertised.

If you have a Newer Diesel engine, you will have a nasty little thing called a DPF

Diesel Particulate Filter or (expensive badly designed and implemented patch to keep greenies happy and stuff up a diesel)

The DPF don't like engine braking, not one little bit.
It will clog the useless patch quite quickly and its expensive to fix'
I would rather wear down my brakes than use engine braking in my new MUX
Brakes may cost a few hundred to replace, a new DPF is thousands.

The grubberment will pocket many thousands of your hard earned cash should you remove this ticking time bomb.
Ensuring that we will all have to eventually fork out even more in the future to keep greenies happy.
We dont have the Particulate problem they have overseas
Most of Australia is windblown enough that the smog is rare, unlike London, Paris or any number of overcrowded and busy cities around the world that sit and wallow in the smog with no breeze to disperse it.
And if it is that big a problem, why not just bad diesel engines from the city?

And just another thing while on my high horse.
Petrol engines put out nearly as much particulate matter as diesels
We are not talking of the soot, which is basically just carbon and some unburnt fuel people worry about when a truck belches smoke.
We are talking about carcinogenic particulates that are invisible.

Diesels actually burn the fuel more thoroughly than petrol.
Petrol pumps particulates into the air just as prolifically as diesel, but they have not put particulate filters on petrol yet because they will suffer the "Great clog" even faster.

But the time will come and it will be all part of the big push for EVs.

And wont that be fun.

[sprintcyclist]

................ Hi Guys,
An update from me. Have bought a new van weighs 2.3 tonne loaded. Towing at 90-95 on highway is averaging 19-21 l/100. have definately discovered to tow in 4th not 5th. The transmission fluid temperature rises too high and even though the revs are lower it is cooking the gears. The slightly higher revs (2300rpm) in 4th @ 95 kph is not using any more fuel but the trans temp is perfectly normal. It is virtually a 1;1 ratio. You will use more fuel towing in 5th and I reckon you will definately damage the gearbox overtime and start to lose gears etc. Just my 2 bobs worth...........

........ Hi guys, I have a v6 2008 GXL with Unichip and Pacemaker extractors... otherwise mostly standard except for sovereign bar, cargo barrier, engel etc. This is a blacktop tourer I mainly use to pull a 2,000kg van. I recently did a 6,000 km trip Perth to the Barossa and return, and average fuel burn was 17.2 lt/100km (total average, van on and van off). I towed in 4th gear at 95km (GPS), and drove to fuel economy, eng temp and trans oil temp data as displayed by the Scangauge. In 4th gear the motor and trans ran cooler, fuel burn was more favourable and the motor was coasting rather than stressing (as it would be if I was in 5th gear and in/out of overdrive). Overall a hassle free trip that came in under budget.
Cheers
Greg............

............. Dan, i have a similar mindset as you in that I bought a v6 Prado (rather than a diesel) to tow my 2400kg enclosed car trailer once a month cos fuel economy to me is secondary and of much more interest to me is to be able to drive at a reasonable pace up and downhills, so a sluggish diesel was never going to cut it.
anyway, I usually tow in 4th as recommended.
ive now fitted a scan gauge and so can monitor trans temps and so have started using 5th dropping it back to 4th when the convertor starts slipping, and temps start to rise.

last trip to Winton towing the trailer was ~20l/100 average in 4th all the way, mostly on cruise at 110k. ..................

.................


https://www.pradopoint.com.au/forum/-12 ... -petrol-12...