Oil & Fuel Lugging a Diesel

[JimMorrissey]

Just wondering if somebody has a reasonable explanation of why lugging a diesel is so bad. The manual says not to "lug" the engine and produce black smoke. I've been running around in a certain gear and hit a pile of compressed topsoil/clay and lugged the machine once in a while. I can't pick the perfect gear every time I'm doing something...maybe it's a bit high once in a while. It's a tractor and it's going to get used. I hope a bit of black smoke from working the machine isn't going to damage the engine /forums/images/graemlins/confused.gif

Any thoughts on where the problem arises for the diesel and what the long terms effects may be.

 

[SkyPup]

Running a diesel engine under high load at low rpm results in too much fueling (overfueling) in the combustion chamber, with raw fuel being sprayed onto the cylinder walls and piston crown without ignition (it cannot ignite unless it has been atomized with the intake air). Some of this fuel is drawn into the crankcase and dilutes the crankcase oil with raw diesel fuel, some of it is cooked onto various metal surfaces, and some of it is burned off as almost raw carbonaceous soot particles. Extended periods of this will overheat the engine causing a myraid of problems due to the concentrated overheating of portions of the combustion chamber where the raw fuel molecules are burned off. Also, it puts severe strain onto the main bearings of the crankshaft and will lead to premature failure as the boundary lubrication provided by the crankcase oil is exceeded by the strain of the mechanics of the lugged engine, causing metal to metal contact.
All in all, not a good thing to engage in more than momentarily. Once you start to see black smoke coming out the exhaust, it's time to downshift. With the GST tranny, downshifting is simple, just hold the throttel steady and shift!

 

[LarryD]

<font color="blue"> All in all, not a good thing to engage in more than momentarily. </font>

So jumping on the throttle when someone is tailgating my truck is not a good thing?

Sure gets 'em to back off. /forums/images/graemlins/grin.gif

 

[SkyPup]

Be careful who your blowing soot all over, could have been some cute young thing who wanted to meet you..... /forums/images/graemlins/grin.gif

 

[JimMorrissey]

Excellent explanation....I'll be sure to drop her down a gear when I notice it happening. I don't do it often, but sometimes it happens briefly and was just wondering how bad it was. Thanks!

 

[TMcD_in_MI]

For a nice long discussion of this, see this link from a year or so ago.

Tom

 

[RoyJackson]

Lugging any engine is hard on the rod bearings.
Deisel bearings are more robust then ones in gasoline powered vehicles...but lugging is still tough on the engines.

 

[cowboydoc]

If you're doing any kind of ground engaging activity you are going to have some lugging at times. Yes the overfueling is a problem and another reason that extended drains do not go well with diesels. But as a general rule temporarily lugging a diesel will not shorten it's life. If you do it continuously yes then you probably will see premature failure.

 

[RalphVa]

My Dad bought a car from Grandpa once. It was a stick shift Plymouth V8. Rode in it once with Grandpa. He just took off in 1st and immediately put it in High. Puttered around the fields at 10-15 mph in high gear.

Very soon after Dad got it, it threw a rod. Lugged too much, too long.

Fiat and Alfa engines were ones you especially didn't want to lug. Most engines now max out their oil pressure at idle or very soon above idle. Fiat and Alfa engines didn't get to full oil pressure until around 1500 rpm. You never wanted them to drop below about 2000 rpm in any gear but 1st. Otherwise, you ran the risk of not having enough oil pressure AND oil flow to the bearings. I owned a Fiat 1100 once that the rods knocked on. Suspect someone didn't drive it with enough engine rpms.

Americans typically didn't learn to shift properly because many of them started out on cars with lots of torque and a really lousy shifter assembly and heavy clutches. European vehicles were almost always easy to shift and needed it because they usually came with small engines because of the price of fuel over there.

Ralph

 

[PBinWA]

</font><font color="blue" class="small">( Americans typically didn't learn to shift properly because many of them started out on cars with lots of torque and a really lousy shifter assembly and heavy clutches. European vehicles were almost always easy to shift and needed it because they usually came with small engines because of the price of fuel over there.
)</font>

I'd rather have lots of torque and a heavy clutch any day of the week. God-bless America (and I'm a Canadian).
/forums/images/graemlins/grin.gif

 

[JimMorrissey]

They also got/get taxed on the displacement of their engines....more CC = $$

 

[ZJ_HR]

Main trend here now in diesel powered cars is 1.4 - 1.5 liter (85-91 cu in) 70-90hp for small city cars, 1.6 liter (98 cu in) up to 110 hp, and 2 - 2.2 liter (122 - 134 cu in) over 110 hp, with consumption 4-7 liter of diesel/100 km (60-33 mpg).
And of course, manual shift in 95% in that car class (5 or 6 speed) /forums/images/graemlins/grin.gif
I'm driving 2.0 liter 90hp common rail diesel, about 4mpg, ususal at 1750-2500rpm.

 

[Youare]

This reminds me of the conversation I had with a gentleman when I was in England several years ago. I noticed that engine dispalcement of most cars was 2 liter or less. I told him that the pick-up truck I drove had a 5.7 liter engine, he almost dropped his teeth exclaiming why do you need such a large engine.

I thought about it for a minute and didn't really know wht to say except that I tend to put alot of weight in the truck and pull heavy things with it. We also like to reach 60 MPH in less than 10 seconds.

Today I am happy driving a car with a 1.7 liter engine manual shift and getting 44 miles per gallon. As for lugging a diesel which was the main topic is black smoke always an indication of lugging? I aways thought that lugging and low RPM went together.

There are times when going along the road and heading up hill at 1800 RPM when I see a trace of black smoke coming from the exhaust. I think more fuel is going in than can be burned for just 10 to 15 seconds, but does this hurt in the long run?

What about low RPM and heavy work and no black smoke is this still lugging?

Randy

 

[SkyPup]

Black smoke or even white smoke (raw unburned fuel) is evidence of overfueling which is what occurs when you lug the engine.

It is not a problem for momentary operation, but if you are going up a long steep grade with a heavy load at elevated altitudes it sure is a major problem due to the extremely high EGT generated and the hot spots in the combustion chamber where raw fuel is touching cylinder walls and piston crowns. If you have a turbocharger, the turbine housing will be way hot and the tips of the turbine will be melting away.....

Low RPM heavy load and no black smoke is not lugging.