Lugging diesels = bad or newfangled myth?

Boomerang1 · Oct 16, 2005

( Hmm.. That thing about letting a diesel idle past 10 minutes is a bunch of bull. ive had truck drivers keep there trucks running overnight(8+ HOURS) and they are still going. ) Truck drivers don't let their engines idle as you may think. The idle is speed is bumped up from the base idle of around 650 - 750 rpms up to around 1000 rpms. When I press the resume switch on the cruise control, the idle will raise to a preset high idle. If I hold down on the switch, I can make the idle go all the way to max or any where in between. This is helpfull when running the PTO for example. Before electronic engines, trucks had a knob that you could pull to raise the idle. It was just a cable that ran to the the throttle linkage. When I idle up the engine to high idle, I can see the temp gauges rise up to operating temp. When you let a diesel engine idle at low speed, it can not build up enough heat and will let carbon build up in the engine.

Boomerang1 · Oct 16, 2005

An engine is being lugged when you are working the engine under load and when you give it throttle, the rpm's will not raise. Don't worry about all the technical stuff. As long as the rpm's will raise whenever you throttle up the engine, you will be just fine. Very simple.

TMcD_in_MI · Oct 16, 2005

( When you lugg your engine, the crank is being held back and the timing is off. )

Thanks HGM, for taking the time to respond to my question. Could you maybe elaborate on your sentence above? I'm having a hard time understanding it. /forums/images/graemlins/frown.gif

For example, what timing is off? Injector timing? Valve timing? Can those change when you lug an engine? Does the fuel burn at a different rate during lugging?

What would hold the crankshaft back?

Sorry if these are too many questions...just trying to understand.

Tom

kevinj · Oct 16, 2005

( As long as the rpm's will raise whenever you throttle up the engine, you will be just fine. )

This what Cummins, Detroit and Cat preached 30 years back, I have used this method for many highway miles and many hours on other equipment and never wiped a bearing or broke a crank.

HGM · Oct 16, 2005

Tom,
The timing I'm speaking of is the combustion timing in relation to the crankshaft speed. Engines are designed to fire just before top dead center, the centrifical force is what keeps it going in the same direction(hence the flywheel and weighted cranks). If that force isnt strong enough, the crank has to fight through TDC.

Whatever your driving, be it a bush hog, tiller, harrows, or just the vehicle itself, if the engine speed isnt sufficient to keep it pulling smoothly it will create a bucking.

This bucking is the drivelines reaction on the slow turning crankshaft, usually magnifying engine firing pulses. I look at it as the engine barely running(before stalling). It obviously cannot produce power to work if it is barely running. When the engine stalls, it cant make it past TDC. If fuel timing is off, it could run backwards... /forums/images/graemlins/grin.gif

As for the other poster's comment on idling semi's. They are totally different like boomerang said they have the systems to kick the idle up. Even 1000RPM is low to idle one all night I would say. To prove it, run your diesel hard and check the temp. Then idle it for at least 10-15min or longer if oyu wish and check the temp. The longer it idles, the cooler it gets....

CT_Tree_Guy · Dec 12, 2005

An engine is being lugged when you are working the engine under load and when you give it throttle, the rpm's will not raise. Don't worry about all the technical stuff. As long as the rpm's will raise whenever you throttle up the engine, you will be just fine. Very simple. 

Boomerang, you are a rare commodity - a genius who can convey an idea in a clear and concise way.

Your point also holds true of course for driving a car or truck, especially when going up a hill. Since all engines hate to be lugged, you want to be in a gear in which you could accelerate if you wanted to. If you can't, drop down a gear. Your engine will thank you. As you said, very simple.