Lugging

[94 formula]

Wait what is considered lugging?
My car can be dumped down to 1100-1200 in 5th gear at just under 40mph and it doesnt make any wierd noises and pulls like a monster. Guess I am asking how do you know if its lugging and what is happening that makes it hard on bearings? I always thought it was putting such a load on the engine the oil film on the bearings was sheared or something in which case the type of oil used would determine at what point the engine would be harmed by lugging. One thing I dont get is if you floor it at 750rpm where the engine has maybe 200lb/ft of torque and then floor it at 2500 rpm where it has 325lb/ft, isnt flooring it at 2500 placing more load on the engine as long as its in the same gear? So why would it matter... does it have to do with oil pressure? Also if you are cruiseing and not accelerating can you cruise in a very high gear, 6th, at 850rpms without lugging as long as the road is level?

[ December 02, 2002, 12:54 AM: Message edited by: 94 formula ]

 

[BOBISTHEOILGUY]

Lugging an engine is where your gearing vers your speed vers your rpm are out of sync. The idea of the higher gears is to be used when an engine doesn't need to produce power but maintain the constant variables being used. The lower the gears 1,2nd and so forth, helps bring the engine up to it's power curve so to pull or produce more power for the purpose of take off. To start out in 3rd or 4th for example, you'll notice that the engine would start to knock if you don't increase the rpms dramatically. This would be below the engines power curve. Diesels for example have a stronger power curve at low rpms unlike gas engines require higher rpms, thus the diesels are better for heavy equipment and such. On take off on a diesel engine(18wheeler) you don't have to apply any fuel, just ease the clutch out and it will pull. On a gas engine, you'd have to apply some fuel/rpm to accomplish the same thing.

In 4stoke bikes vers 2 stroke bikes, the power curve is lower for the 4 stroke but with a 2 stroke it requires higher rpms.

What you'll find is that when lugging an engine, the engine will start to knock. This does put a strain on the motor as it will and can cause the engine to "suck a valve" down into the cyl and do some extreme serious damage.

As for lubrication, The oil pump would not be producing as much oil pressure due to lower rpms and the demand on the engine would be greater. Because of this the lower rpm would produce less hydrodynamic film or weaker film, so when the power is applied, it would push out the film easier as there would be less there, and this would cause the oil to shear at a higher rate than an engine running full. Oil pressure is actually a reading of back pressure of the oil in the bearings and throughout the engine. Think about this a minute..

Notice that at each point where the oil turns throughout this engine, this is where oil back pressure is created. When an engine has low oil pressure, this is due to worn parts,(bearings and such) and that the engine cannot hold oil pressure but allows the oil to pump freely. So in the case of a worn engine, lower oil pressure. So, when you have an engine at idle, low oil pressure exists, and when you jump on the gas, that lower oil pressure or lower film hasn't got enough time to increase the film as you well know that oil pressure has to increase and lags behind rpms slightly, so, there is where shearing will cause scuffing/wear. This would normally be around the rod bearings, and pins more than anywhere else. This is primarily why so many you guys that hot rod an engine will wear out an engine before someone that is easier on acceleration.

[ December 02, 2002, 12:34 PM: Message edited by: BOBISTHEOILGUY ]

 

[MolaKule]

Oz asked the same question on a different thread:

I don't think occasional lugging will do much damage. Howver, it should be avoided if possible.

As I understand it, lugging is low engine rpm caused by a mismatch in vehicle/engine speed, and improper gear selection under high loading conditions. Lugging creates "shock" loads to the piston and crankshaft. You also have a momentary heat rise, since the coolant moves slower than normal.

-How does oil protect the engine in this situation?

By providing lubricating films and cooling.

- Is there a particular additive in the oil that helps?

Anti-wear and Friction modifiers certainly help here, since your oil pressure is probably too low to keep hydrodynamic lubrication going. A good boundary additve as backup certainly helps.

- What engine internals gets worn down prematurely?

I would say the wrist pin, the connecting rod, and the large bearings in the engine get stressed the most.

- Does it affect other non-engine related components?

The timing chain or timing belt is also seeing these shock loads. And you will get surges in fuel delivery since the computer is attempting to compensate.

- How in the world do I prevent this!?!?!?

Get the clutch adjusted and make sure the rpm's are high enough to produce a sufficient amount of torque to move the vehicle. I had rather burn clutch material than damage internals.

 

[Patman]

Another easy method of prevention, just drive cars with automatics!

 

[satterfi]

quote:

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Originally posted by Patman:
Another easy method of prevention, just drive cars with automatics!

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The only time I have lugging is at a stop and I think my bike is in first when it's actually in second. The bike makes all kind of ugly noises on take off.

I hate to think of all the unnecessary stresses that puts on things.

Perhaps having on oil with overkill barrier additives might help here.

 

[OneQuartLow]

My own possibly flawed opinion on lugging causing damage is that it's valid in principle but shouldn't be a problem for Joe Public driving "properly functioning" factory engines.

My reasoning: Factory engines are expected to see a wide variety of driving conditions and habits and last for at least the warranty period. Therefore they're designed to have pretty good pressure and protection throughout their power ranges. If the engine were worn, or had some other problem that caused abnormally low pressure, then it could start to shear excessively. Or if the engine was designed for racing and compromised low RPM pumping to minimize HP loss...you see where I'm going.

Anyway, it's going to depend on the specific engine design and its condition. Recent, proven, factory engines shouldn't have the problem. If it's a known weakness in yours then install a high volume pump so you're safe loaning the car to granny. Surely, lugging moves you toward a boundary of design considerations but it shouldn't be an issue in most cases. Good to know about the possibility though for those situations where it could hurt.

Of course, jump all over me if you disagree. This place has already revised several of my old opinions.

David

 

[Ira]

quote:

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Originally posted by BOBISTHEOILGUY:
What you'll find is that when lugging an engine, the valves will start to knock. This does put a strain on the motor as it will and can cause the engine to "suck a valve" down into the cyl and do some extreme serious damage.

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Say what? Valves knock or get sucked into an engine? Not to be insulting or anything but running an engine at low speeds should never cause a problem like this. Lugging should have no abilit to effect the valves at all.

Lugging can concievable cause the bearing to get hammered and depending on the engine it may lead to pinging or knocking which can cause various other problems. If an engine has sufficient oil pressure and the engine is turning fats enough to keep the oil film alive there is no downside to lugging an engine. If you drive something with a low cylinder count or big cams you might find that under some RPM the engine is not smooth, which can cause wear to the chassis and drivetrain.

Ira

 

[BOBISTHEOILGUY]

quote:

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Originally posted by Ira:

Originally posted by BOBISTHEOILGUY:
[qb]What you'll find is that when lugging an engine, the valves will start to knock. This does put a strain on the motor as it will and can cause the engine to "suck a valve" down into the cyl and do some extreme serious damage.

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I meant to say the ENGINE will start to knock not the valves

 

[widman]

Lugging puts the engine under load, and I believe therefore increases the wear of the rings, as in the charts shown here.
http://www.swri.edu/4org/d03/vehsys/filfine/rtwear.htm

 

[OneQuartLow]

Widman, I've seen that page before in a discussion about the results of poor filtration. Very interesting test rig, no?

But I must be reading those charts wrong. It looks like they show lugging is good for the engine tested?

The legend is tough to read but chart 1 looks to show peak compression ring wear at ~.58mg/min with 100% load at 2500RPM, but dropping below .1 for 100% load at low RPM. The second chart seems to show similar results with wear being a function of high RPM (peaking with acceleration) & time.

Wish they talked more about the test and not the technology. Although, we need to get bob one of these things for Christmas. :thumbsup: What could be more perfect for comparing oil effectiveness?

David