Can short shifting actually cause wear to a motor?

[biodiesel]

I was searching through past UOAs specifically concerning Honda motors and I found this one here:

https://bobistheoilguy.com/forums/threads/pp-5w30-8198-miles-on-08-civic-si-high-pb-sn.121956/

Regarding point #4 the thread creator says "Short shifting for fuel economy could be causing some sort of stress on the bearings."

Is this true and/or possible? How exactly would short shifting and not stressing the motor actually result in wear?

 

[Brons2]

lugging the engine, I would think. If you try to accelerate at lower RPMs you may be lugging it.

 

[fsskier]

It seems that people have worried about "lugging" a motor forever, but I have never seen any evidence of anything to worry about.

For sure, my 5 speed manual cars, with very high overall top gears in them are operating at low rpm, often at large throttle openings on hills, etc.

They are lasting 3 times longer than the old high rpm "all wound up" cars I drove years ago.

I always use the highest gear that will do the job, our 5 speed cars are running 300k miles with motors that seem like new so....

 

[CATERHAM]

I read somewhere that engine wear increases with the square of piston speed, so short shifting is of course a good thing.

Lugging an engine is a whole different animal and it is not a good thing.

 

[JT1]

My greatest fear with "lugging" an engine is that under the right circumstances detonation may occur.

With todays fuel/spark control the engine may just about shut off before there is any actual damage done to the engine via detonation.

 

[Craig in Canada]

Originally Posted By: JT1
My greatest fear with "lugging" an engine is that under the right circumstances detonation may occur.

With todays fuel/spark control the engine may just about shut off before there is any actual damage done to the engine via detonation.


The problem is that you have very high load on the main bearings without corresponding oil pressure to maintain separation.

This high load is due to two factors - large throttle angle and low piston speed.

Unless it's a diesel or some other engine DESIGNED to produce high torque at low RPM don't do it.

 

[Shannow]

Oil pressure does NOT provide separation of journals and bearings in an IC engine.

 

[ps49556n]

Originally Posted By: JT1
My greatest fear with "lugging" an engine is that under the right circumstances detonation may occur.

With todays fuel/spark control the engine may just about shut off before there is any actual damage done to the engine via detonation.


You should be more worried about blowing a head gasket as that is a common result of lugging an engine under severe load. While short shifting done properly is for the most part harmless, you could be lugging or bogging down the engine and not even realize it since you are so focused on fuel economy.

I used to be one of those drivers always short shifting and focused on the best fuel economy but have come to believe that with a properly maintained engine, it is BETTER to drive normally, with some relatively high revving to keep everything clean inside.

 

[1999nick]

On a modern high rpm engine, what rpm do you guys consider to be lugging?

 

[Captain_Klink]

I prefer to shift normally, it is more fun that way, and i doubt i really waste any significant gas. on the other hand, i cruise in a fairly high gear, and if i need torque at cruising speed, i only use VERY GENTLE throttle, to avoid wearing out the bearing.

 

[saaber1]

High load, low rpm (lugging) is bad. Low load, low rpm isn't going to hurt anything.

One example is the modern dual clutch gearboxes such as VW's DSG. In auto mode, if you are puttering around town like a grandma, it shifts at ridiculously low rpms and goes all the way into 6th gear at 35mph. It is designed that way. But if you get on it, or are pulling a hill, etc. it shifts completely differently and doesn't short shift nearly as much.

Also sport mode, where it is expected to operate in a high load (getting on it, WOT, etc.) it shifts completely differently and even will shift beyond redline if ur driving it hard.

 

[Eddie]

I shift and run my engines at the lowest RPM that they will run smooth. As Shannow said oil pump pressure does not equate to bearing pressure. Hydrostatic oil pressure is what separates the bearing from the journal.

 

[djlinux64]

If you are keeping the RPMS above idle RPM you should have enough oil pressure to be OK. Besides, 800 ppm ZDDP and other AW/EP should prevent lugging wear. Don't worry about it.

 

[SteveSRT8]

Old wives tale.

In a modern drive-by-wire car there is no such thing as 'lugging'. There can be no detonation either.

This is all old baloney from about 1956!

Keep it above idle and short shift it all you want. The computer will handle the rest!

 

[tig1]

Originally Posted By: SteveSRT8
Old wives tale.

In a modern drive-by-wire car there is no such thing as 'lugging'. There can be no detonation either.

This is all old baloney from about 1956!

Keep it above idle and short shift it all you want. The computer will handle the rest!


Not sure I understand you. If you have a 5 speed and start off in 3rd there will be no lugging? Lugging has to do with being in the wrong gear for the speed you are at and trying to accelerate.

 

[lexus114]

Originally Posted By: SteveSRT8
Old wives tale.

In a modern drive-by-wire car there is no such thing as 'lugging'. There can be no detonation either.

This is all old baloney from about 1956!

Keep it above idle and short shift it all you want. The computer will handle the rest!



Uh,...What ?

 

[fsskier]

[/quote]

Not sure I understand you. If you have a 5 speed and start off in 3rd there will be no lugging? Lugging has to do with being in the wrong gear for the speed you are at and trying to accelerate. [/quote]

Starting out in third gear would likely cause greatly increased clutch wear. I leave it in fifth for the long upgrade home, about 1,100 rpm at 35 mph. The throttle is pretty well open but the cars maintain speed nicely. No reason to shift, or accelerate, there are cars in front of you!

The 86 Taurus MT5 (4cyl, 5speed stick) did this for 20+ years and 200+K miles, then went to the dump with a perfect motor and a rust failing frame. Our two Escorts, same treatment, same results.

I know of no technical paper or science based evidence that lugging is bad... assuming that you are not into detonation. Never blew any headgaskets either!!

 

[mechtech2]

I also have come to the conclusion that 'lugging' an engine is harmless.
You are not producing a lot of power at low RPMs, and I have never seen this bearing pounding thing in an engine.
Of course, use an appropriate oil.

There may have been validity about not lugging an engine with very old cars with substandard materials and fit. And oils were not so hot then, either.

 

[lexus114]

Originally Posted By: fsskier
[/quote]

Not sure I understand you. If you have a 5 speed and start off in 3rd there will be no lugging? Lugging has to do with being in the wrong gear for the speed you are at and trying to accelerate.


Starting out in third gear would likely cause greatly increased clutch wear. I leave it in fifth for the long upgrade home, about 1,100 rpm at 35 mph. The throttle is pretty well open but the cars maintain speed nicely. No reason to shift, or accelerate, there are cars in front of you!

The 86 Taurus MT5 (4cyl, 5speed stick) did this for 20+ years and 200+K miles, then went to the dump with a perfect motor and a rust failing frame. Our two Escorts, same treatment, same results.

I know of no technical paper or science based evidence that lugging is bad... assuming that you are not into detonation. Never blew any headgaskets either!!



Thats because it`s common sense !

 

[Geonerd]

I suspect that the bearings of most modern engines are sized and designed to maintain 'enough' oil film throughout the entire operational RPM / Throttle range.

Dynamic load does go up with the square of RPM. Static load is largely proportional to torque output. The bearing sees the sum of these two.

As shown by our friend the Stribeck Curve, oil film thickness increases with RPM and oil viscosity.

Oil film thickness may (or may not) becomes a problem near redline, when dynamic loads become huge, or near idle when the low bearing surface speeds generate only a thin oil film.

Slapping supercharger on an engine increases the torque output greatly and has the same effect as running super thin oil. This can do very bad things at low RPM. "Super Lugging"

AFAIK, F1 and MotoGP bikes run super thin oil (0w-5 or thereabouts) and NEED to idle at ~5K RPM. Anything lower constitutes 'lugging,' and will destroy the bearings in short order!

FWIW. As a mild economy nut driving a stick, I do tend to run fairly high throttle (50~70%) around 1500~2500 RPM for short bursts. Since starting this, I've made a point to run somewhat thicker oil. (HTHS of 3.5 to 4) I've got an OCI coming up in a few months and will post analysis numbers.