I think I saw that video or a similar one. I suppose they would know.
Does coasting at low RPM's cause excessive wear to Dual Mass Flywheel?
- Thread starter Saikou
- Start date
I think I saw that video or a similar one. I suppose they would know.
I've put 208.000 km (130.000 miles) on my car and it still has the factory flywheel.... and it doesn't show any sympton of wear.... but my plans are keeping the car forever, thus my interest on looking after it.
60.000 miles of lifespan for a DMF sounds riddiculous for me BTW, I think most of them last way longer according to my experience.
I've only had 1 DMF failure and it was on a MK4 Mondeo 1.8TDCi at 168,000miles. That was mainly motorway miles and the engine had been remapped from 125bhp & 235lbft to 150bhp & 300lbft.
I swapped out a dual mass flywheel for a standard flywheel, and switched back within a week. What I found is that with my reasonably smooth V6, anything below ~1,500 RPM with the single mass flywheel made the transmission sound like it was being hammered to death, combined with significant vibration in the car. Back to dual mass, smooth as silk from idle up, even under load. My takeaway was that the DMF is absorbing a tremendous amount of shock-load vibration and that I should keep the engine speed up. Also that I like dual mass flywheels. With an automatic transmission, you have a torque converter that is generally unlocked below certain speeds, and some that are nearly locked at lower speeds. The torque converter is a fluid connection, it will absorb most of the shock and vibration.
FWIW, my oem dual mass flywheel was fine when I pulled it out at nearly 200K miles and ~16 years. They can last for a long time.
At low rpm each ignition of fuel "pulses" the DMF spring component and wears it out. At higher RPM the pulses are faster and the springs/rubber that separates the two parts of the flywheel doesn't compress on each ignition. Think of it like driving down a washboard road. At slow speeds it will rattle your teeth out, but faster the suspension doesn't react to each bump and runs smoother.
I don't know that there can be a fixed rpm which is damaging to the DMF for all vehicles.
Essentially the DMF is working too hard if without it, the vehicle would be perceived to be lugging.
So what's lugging ?
"Lugging is what we feel when the cyclic variations in the crankshaft rotational speed become excessive and produce shock loading on the engine components"
The crankshaft does not ever rotate at a perfectly even speed although at higher revs we don't notice this. Every revolution the crankshaft speeds up and slows down in between each cylinder firing with only the flywheel inertia to even out the power strokes. The perception of lugging at any particular engine revolutions is therefore directly related to the engine load (the crankshaft will slow down more between power strokes under heavy load), the mass of the flywheel (for any given load a lighter flywheel will slow down more between power strokes) and the number of cylinders (more cylinders equals shorter time between cylinder firing.) So an engine with a heavy flywheel will not feel it's being lugged at the same revs or load as one with a lighter flywheel and a 6 cylinder will not be perceived to lug at the same revs as a 4 cylinder. So if there can't be a fixed rpm to define lugging then there can't be a fixed RPM below which the DMF is damaged.
Throw in the fact that some modern forced induction engines develop maximum torque as low as 1500 RPM and I am thinking the manufacturers will have designed the DMF to cope otherwise we couldn't be expected to actually use that torque. Conversely if 1500 RPM was going to wreck the DMF wouldn't they have tuned the engine for peak torque at a higher RPM.
If in practice you don't routinely use maximum low rev torque and I would suggest that applies to most of us, then the DMF should cope.
Essentially the DMF is working too hard if without it, the vehicle would be perceived to be lugging.
So what's lugging ?
"Lugging is what we feel when the cyclic variations in the crankshaft rotational speed become excessive and produce shock loading on the engine components"
The crankshaft does not ever rotate at a perfectly even speed although at higher revs we don't notice this. Every revolution the crankshaft speeds up and slows down in between each cylinder firing with only the flywheel inertia to even out the power strokes. The perception of lugging at any particular engine revolutions is therefore directly related to the engine load (the crankshaft will slow down more between power strokes under heavy load), the mass of the flywheel (for any given load a lighter flywheel will slow down more between power strokes) and the number of cylinders (more cylinders equals shorter time between cylinder firing.) So an engine with a heavy flywheel will not feel it's being lugged at the same revs or load as one with a lighter flywheel and a 6 cylinder will not be perceived to lug at the same revs as a 4 cylinder. So if there can't be a fixed rpm to define lugging then there can't be a fixed RPM below which the DMF is damaged.
Throw in the fact that some modern forced induction engines develop maximum torque as low as 1500 RPM and I am thinking the manufacturers will have designed the DMF to cope otherwise we couldn't be expected to actually use that torque. Conversely if 1500 RPM was going to wreck the DMF wouldn't they have tuned the engine for peak torque at a higher RPM.
If in practice you don't routinely use maximum low rev torque and I would suggest that applies to most of us, then the DMF should cope.
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