lugging a diesel engine

I have heard that lugging a diesel engine is particularly bad for it. I was wondering why this was. Also, is lugging any type on engine bad for it and what kind of damage could result?

The only reason I can think of is that diesels run hotter when you add more fuel as opposed to gas engines which will run cooler as the A/F ratio is enrichened. Lugging an engine with your foot into it will cause it to load up with fuel, but unless you did it for an eccessive amount of time I don't think it would really do anything but waste fuel.

Lugging any engine (excessively low revs while giving it lots of throttle )is just bad because it places excessive strain on the reciprocating components, such as engine bearings, connector rods, crankshaft and pistons.

These loads increase as the engine revs slower, while producing a certain amount of power.

Diesel engines are much more durable and built more strongly than gas engines, and are much less susceptable to damage from lugging than gas engines. Drivers of big rigs lug their engines all the time. The next time you see an 18 wheeler thats loaded pull away from a traffic light, listen to the engine. You will notice the driver will release the clutch while the engine is just idling, and not give it any throttle until the rig is actually moving and the clutch is released. This requires 'lugging' the engine under load for a second or two. This is normal procedure. If you were to drive that big rig the wayt you drove a car - give it throttle and revs while releasing the clutch - you would burn up the truck clutch quickly and break the driveshaft U-joints in no time.

The only reason I can think of is that diesels run hotter when you add more fuel as opposed to gas engines which will run cooler as the A/F ratio is enrichened. Lugging an engine with your foot into it will cause it to load up with fuel, but unless you did it for an eccessive amount of time I don't think it would really do anything but waste fuel.
Well, yes and no. The diesels exhaust gas temps run hotter as you add more fuel, but they are still in the 800-1000 degree range as opposed to a gas engine's 1200-1800 range. The diesel engine itself is very resistant to thermal overloading from lugging.

You should never lug any engine, its just that lugging for a gas engine is typically in the 500-1500 RPM range and those big rigs sometimes redline at 2200 or less, so their "lug" range is 500-700 :)

Danny350 is spot on, though, just an opinion to add to his excellent post. MagicRat is also spot on. I'm a little late to this party :D

Lugging an engine isn't dangerous, the load on the engine parts is MUCH higher at high engine speeds and loads. I know there have been research on this since low engine speed combined with high load have been desirable for low fuel consumption. The only danger that I know have been mentioned is the increased vibrations which for example can wear out the rubber engine mounts faster.

Diesel engines runs cooler due to the fact that they use air excess. A turbocharged diesel usually have a maximum turbine inlet temperature of 700-800 degC while a turbocharged gasoline engine has 900-1050 degC.

I know there have been research on this since low engine speed combined with high load have been desirable for low fuel consumption.

That makes sense for gassers, but I don't think it applies to diesels. On a gasser, it is based on the throttle movement and fuel... well I'm not sure exactly how it works, but diesels don't have a throttle, so it's probably not applicable.


Lugging also depends on what kind of diesel you're looking at. On my Golf for example, I don't worry about lugging because of stress or lubrication issues- I just don't want my intake plugging up. This diesel has exhaust gas recirculation(EGR) as well as a crankcase vent(CCV). So you get a little bit of sootie exhaust coming through, combined with a little oil vapor from the CCV, and viola, what a mess! The EGR is more active in some situations than others, and low rpms is one of them. Also, you will likely have more soot at low rpm and high load, becuase you're just dumping fuel without getting much more air. If you lug frequently, you'll end up with a plugged intake, which will make the car smoke, use more fuel, and lose power.

Lugging an engine isn't dangerous, the load on the engine parts is MUCH higher at high engine speeds and loads. I know there have been research on this since low engine speed combined with high load have been desirable for low fuel consumption. The only danger that I know have been mentioned is the increased vibrations which for example can wear out the rubber engine mounts faster.

Diesel engines runs cooler due to the fact that they use air excess. A turbocharged diesel usually have a maximum turbine inlet temperature of 700-800 degC while a turbocharged gasoline engine has 900-1050 degC.


Sorry this is incorrect
Lugging an engine is one of the most abusive things you can do to an engine. The load on the reciplicating components is much higher than at an engine speep closer to its peak torque. This is not to mention the fact that the engine recieves less lubrication from crank shaft splash ect.

you are correct about diesel engines running cool because of lean mixtures though. Diesel engines can run at increadable lean mixtures at idle or light load conditions. Also hence the reason that 3 way cats don't work on them