Does coasting at low RPM's cause excessive wear to Dual Mass Flywheel?

[Saikou]

Messing with speedbumps while driving my diesel car around city with manual transmission could be a PITA, since it makes me shift gears over and over again, so I avoid shifting between third and second by coasting in third gear thus lowering the speed before a speedbump, and after that I just speed up again accelerating smoothly. So the question is:

Does coasting in third gear at 1.100 rpm or simply driving at 1.100 rpm with low acceleration will cause excessive wear to the DMF?

I'm wondering if it would be better to downshift to second... but clutching will cause some amount of wear to the DMF anyways... so I'm wondering what's better

I'm not implying to kickdown the gas pedal at low RPM's, just coasting or gentle acceleration to rev-up the engine smoothly

 

[Bailes1992]

I once watched a video on YouTube from LUK who suggested that any driving below 1600rpm would cause premature wear to the DMF. That was about 10 years ago now maybe? I've always driven above 1600rpm since and don't let my engine labour at all.

 

[KrisZ]

There are people that insist on driving above certain RPM because in their head it will make things last longer. If you read about it that RPM is all over the place. Some swear anything below 2k rpm is lugging, some below 2.5krpm, some below 1.8krpm etc. People's imagination has no limits. They talk about lugging or working the engine hard when in fact they probably never experienced an engine that is truly lugging.

Mechanical things tend to give feedback to the user. If everything is smooth and the engine can accelerate smoothly at a moderate pace from whatever RPM you drive, it means that RPM is OK.

 

[Bailes1992]

There are people that insist on driving above certain RPM because in their head it will make things last longer. If you read about it that RPM is all over the place. Some swear anything below 2k rpm is lugging, some below 2.5krpm, some below 1.8krpm etc. People's imagination has no limits. They talk about lugging or working the engine hard when in fact they probably never experienced an engine that is truly lugging.

Mechanical things tend to give feedback to the user. If everything is smooth and the engine can accelerate smoothly at a moderate pace from whatever RPM you drive, it means that RPM is OK.

I live in a place where the majority of our cars and manuals, and manuals are every easy to make lug around. People follow the on-board advice about changing gear and usually this results in a low-rpm high-load situation. While this might be slightly better for fuel economy and emissions, it doesn't feel 'right' to me.

 

[KrisZ]

I live in a place where the majority of our cars and manuals, and manuals are every easy to make lug around. People follow the on-board advice about changing gear and usually this results in a low-rpm high-load situation. While this might be slightly better for fuel economy and emissions, it doesn't feel 'right' to me.

OP described nice and smooth acceleration in 3rd gear from 1100 RPM, what exactly "doesn't feel right" in this scenario?
I've driven diesels with dual clutch automatic gearboxes and they behave the same, that is allow the engine to go down to 1k-1.1k RPM and these have dual mass flywheels too.

I've lugged many engines when I was young, motorcycles, tractors, cars, diesel, gas, two stroke. You definitely feel it. It's not smooth at all and in some cases quite violent.

 

[Saikou]

OP described nice and smooth acceleration in 3rd gear from 1100 RPM, what exactly "doesn't feel right" in this scenario?
I've driven diesels with dual clutch automatic gearboxes and they behave the same, that is allow the engine to go down to 1k-1.1k RPM and these have dual mass flywheels too.

I've lugged many engines when I was young, motorcycles, tractors, cars, diesel, gas, two stroke. You definitely feel it. It's not smooth at all and in some cases quite violent.

this is exactly what I was thinking about.

the thing is that my BMW seems to run perfectly well at 1.100 or 1.200 rpm at 30 km/h in third gear coasting or even accelerating smoothly, and I don't know if the car is so incredibly well made in terms of torque, power and soundproofing that I can't feel it struggling or if it's indeed running 'comfortably' so to speak.

I also think that the engine may have way enough power to accelerate effortless from low rpms , but the clutch and gearbox could be under stress meanwhile...

 

[billt460]

If I drive either my Jeep or my Toyota lightly, they never see anything above 2,000 RPM. (Both have 8-speed automatics). Everytime they're taken out they spend the first 5 minutes idling down the hill into town.

Even going back up they're turning 1,500 RPM max.

I can't see how that can possibly wear anything out faster.

 

[Bailes1992]

OP described nice and smooth acceleration in 3rd gear from 1100 RPM, what exactly "doesn't feel right" in this scenario?
I've driven diesels with dual clutch automatic gearboxes and they behave the same, that is allow the engine to go down to 1k-1.1k RPM and these have dual mass flywheels too.

I've lugged many engines when I was young, motorcycles, tractors, cars, diesel, gas, two stroke. You definitely feel it. It's not smooth at all and in some cases quite violent.

My Duster will pull from 1500rpm, but there is a noticeable vibration through the car that doesn't exist if I drop a gear and start pulling at 1800rpm-2000rpm.

Most people would quite happily pull from 1500rpm or even force it through the 'flat spot' from 1200rpm onwards but it's got to be adding wear to the DMF.

I had a 2020 BMW 520d with the ZF 8HP and that loved to run the engine around 1100-1200rpm but when you tried to accelerate you could feel the NVH from the engine that just didn't exist if you ran with the gearbox in 'sport' that brought the revs up a few hundred RPM.

 

[SHOZ]

I drive both my manuals like a diesel but light acceleration. The Gen Coupe is a dual mass. The first version of it they came out with suffered broken springs usually as a failure. No problem with the 2nd version. It's made for more HP though.

It really screws up the LTFT though on the Accent, the Gen Coupe turbo has a tune and it's sweet spot for torque is around 2500-3200.

 

[KrisZ]

this is exactly what I was thinking about.

the thing is that my BMW seems to run perfectly well at 1.100 or 1.200 rpm at 30 km/h in third gear coasting or even accelerating smoothly, and I don't know if the car is so incredibly well made in terms of torque, power and soundproofing that I can't feel it struggling or if it's indeed running 'comfortably' so to speak.

I also think that the engine may have way enough power to accelerate effortless from low rpms , but the clutch and gearbox could be under stress meanwhile...

Don't worry about it. Clutch and gearbox is stressed by engine torque. So if you are not demanding hard acceleration from low RPM, just driving around gently, you are not stressing anything.

 

[Saikou]

If I drive either my Jeep or my Toyota lightly, they never see anything above 2,000 RPM. (Both have 8-speed automatics). Everytime they're taken out they spend the first 5 minutes idling down the hill into town.

Even going back up they're turning 1,500 RPM max.

I can't see how that can possibly wear anything out faster.

you americans should bear in mind one important thing about this term: you usually drive cars with automatic gearboxes, but in my country the norm are manual gearboxes.... and when we put in the same equation a 6-speed manual gearbox and a 4 cylinder diesel engine (which creates way more vibration) the consequences are catastrophic.

There are lots of cases of DMF broken, with bills up to 1.500 Euros to fix it, especially when it comes to french vehicles (Peugeot 406, 407 most of cases, but it's extensive to every diesel engine)

My 06' BMW 320d still runs as good as new, but with more than 200.000 kilometers it comes a time when you have to look after some things to avoid a mess, and this is why I'm so interested on this topic

 

[KrisZ]

My Duster will pull from 1500rpm, but there is a noticeable vibration through the car that doesn't exist if I drop a gear and start pulling at 1800rpm-2000rpm.

Most people would quite happily pull from 1500rpm or even force it through the 'flat spot' from 1200rpm onwards but it's got to be adding wear to the DMF.

I had a 2020 BMW 520d with the ZF 8HP and that loved to run the engine around 1100-1200rpm but when you tried to accelerate you could feel the NVH from the engine that just didn't exist if you ran with the gearbox in 'sport' that brought the revs up a few hundred RPM.

Engines vibrate differently at different RPM. The ones with balancing shafts hide it quite well though.
So if a little bit of vibration is bad at low RPM, how about when it happens at high RPM?

In America, the land of automatic transmission, cars run at low RPM all the time. My minivan always shifts below 2k rpm and drops to around 1.2krpm when driving normally. Heck, it even cruises at 60mph at 1500rpm. Millions of cars do it all the time.

 

[Bailes1992]

Engines vibrate differently at different RPM. The ones with balancing shafts hide it quite well though.
So if a little bit of vibration is bad at low RPM, how about when it happens at high RPM?

In America, the land of automatic transmission, cars run at low RPM all the time. My minivan always shifts below 2k rpm and drops to around 1.2krpm when driving normally. Heck, it even cruises at 60mph at 1500rpm. Millions of cars do it all the time.

I think you might be missing the point that these at 4 cylinder diesels that will vibrate at low RPM's and there's nothing you can do about it. They'll go from 2,000rpm to 4,500rpm as smooth as silk though.

 

[KrisZ]

I think you might be missing the point that these at 4 cylinder diesels that will vibrate at low RPM's and there's nothing you can do about it. They'll go from 2,000rpm to 4,500rpm as smooth as silk though.

There is nothing "smooth as silk" in a 4 cylinder, diesel engine when you compare it to an equivalent gasoline engine.
You're equating vibration with bad things. So how come diesel engines last longer than gasoline engine despite having more vibrations?

Also, diesel engines have lots of torque from very low RPM and a very low redline, meaning they are meant to be driven at low rpm.

 

[Bailes1992]

There is nothing "smooth as silk" in a 4 cylinder, diesel engine when you compare it to an equivalent gasoline engine.
You're equating vibration with bad things. So how come diesel engines last longer than gasoline engine despite having more vibrations?

Also, diesel engines have lots of torque from very low RPM and a very low redline, meaning they are meant to be driven at low rpm.

Depends what you class as low RPM? Peak torque comes in at 1,800rpm. Doesn't mean they're happy to be lugged around at 1,200rpm.

I try to drive my Duster by using 2,000-3,000rpm to accelerate and drop down to 1,800rpm to 2,000rpm to cruise. When towing I usually have to add 1,000rpm onto all of them.

 

[SwampSurvivor]

There are people that insist on driving above certain RPM because in their head it will make things last longer. If you read about it that RPM is all over the place. Some swear anything below 2k rpm is lugging, some below 2.5krpm, some below 1.8krpm etc. People's imagination has no limits. They talk about lugging or working the engine hard when in fact they probably never experienced an engine that is truly lugging.

Mechanical things tend to give feedback to the user. If everything is smooth and the engine can accelerate smoothly at a moderate pace from whatever RPM you drive, it means that RPM is OK.

My ford modulars don't seem to indicate they aren't happy running at lower RPMs, but I can tell from doing a lot of towing that there simply isn't any torque below 2100 RPM in my 5.4. It's like a light switch. And then it pulls strong from 2300 until it hits the rev limiter. It's just happier power and fuel wise at higher RPM. Similar with my 4.6 powered Marquis, it has nothing until it hits like 35 in 1st gear then it pulls strong until it shifts out of 1st at 53MPH ... then falls on its face when it hits 2nd

 

[KrisZ]

Depends what you class as low RPM? Peak torque comes in at 1,800rpm. Doesn't mean they're happy to be lugged around at 1,200rpm.

What is lugged? What is happy? How does peak torque play into the "happiness"?
Again, millions of cars do it, where exactly is the problem?

 

[Bailes1992]

What is lugged? What is happy? How does peak torque play into the "happiness"?
Again, millions of cars do it, where exactly is the problem?

If my engine is causing vibrations to emanate through the cabin and refuses to accelerate responsively and without an increase of NHV during the acceleration process, and none of those things are applicable in a lower gear, then I would say my engine is not 'happy'.

Also would like to add I'm getting 63-69mpg out of my Dacia Duster with this 'high RPM' driving style.

Another benefit of the slightly raised RPM's is the extra engine braking when coasting.

 

[barryh]

What is lugged? What is happy? How does peak torque play into the "happiness"?

Lugging is what we feel when an engine is loaded at low revs producing vibration and shock loading as a direct result of cyclic variations in the crankshaft rotational speed. Every revolution the crankshaft speeds up and slows down in between the power strokes with only the flywheel inertia to help maintain an even rpm.

This perception of lugging at any particular engine revolutions is therefore directly related to the engine load (it will slow down more between power strokes under heavy load), the number of cylinders (more power strokes per revolution) and the mass of the flywheel. So an engine with a heavy flywheel will not protest as much as one with a lighter flywheel and a 6 or 8 cylinder engine with more power strokes per revolution and particularly if it has a torque converter or dual mass flywheel as an in built shock absorber will hardly be perceived to lug at all even at low revs.

If lugging was a major problem you would have to ask why manufacturers have developed modern forced induction engines to develop peak torque as low as 1500 rpm as that implies it's safe to use that torque. I'm guessing the reason we have dual mass flywheels is that without them these engines would lug like crazy at 1500 rpm.

I have a kompressor engine with manual box and it very rarely lugs unless I do something brutal like select the wrong gear, I don't provoke it by putting the pedal to the floor at such low revs but I do cruise lightly loaded at low revs without any issues. 78,000 miles so far on the original dual mass flywheel without problems.

 

[dumkid]

What wears out dual mass flywheels is vibration. At low rpm and high load, the engine vibrates more. I would downshift, just because the cars i drive don't like accelerating when they're under 1300 rpm.
If it was my car I would see if they make a single mass flywheel and if the extra vibration from the smf causes any issues. And most dual mass flywheels last over 60,000 miles, so if you aren't keeping the car that long i wouldn't worry.