Lugging diesels = bad or newfangled myth?

[Dargo]

Two words: oil pressure. If you lug the engine to the point where you lose appropriate oil pressure it does not matter how heavy, how technically advanced, how superior your engine is, you will begin damage. My diesel mechanic buddy has a Dodge with a Cummins diesel in it that consistantly runs in the upper 12 second range in the 1/4 mile. To put that in perspective, that will embarrass a new Corvette owner; especially when he realizes a 1300 pound 6 cyl. diesel in a 6500 pound truck just out ran him in a drag race! This mechanic knows diesels. He strongly tells me not lug to the point where I drop oil pressure. Also, as pointed out in an earlier post, EGT's (exhaust gas temp) will rise to the point to where it is certainly possible to begin to melt engine parts. /forums/images/graemlins/frown.gif That is not a good thing!

My 8000 pound pickup with a Cummins does not run as fast as his, but I can out run a new Chevy pickup with a 6.0 liter, and the Dodge pickup with a Hemi. Besides, it's fun to make them back off when they can't see from the smoke I'm blowing out when I pull away from them. /forums/images/graemlins/grin.gif Go diesel!!

 

[getut]

Ok... the oil pressure reason actually sounds valid and should be a legitimate concern. This of course would vary from design to design, but at approximately what RPM would an oil pump lose effectiveness?

I absolutely despise running my engine at full rated speed because of the noise and vibration being at LEAST double than when running at say 2200 RPM. I guess for people like me who run at a lower RPM, there is no arguing that a very good synthetic oil which typically has a much higher film strength than a mineral oil would provide some offset to not running at higher RPM's to keep the oil pressure as high.

I do doubt that lugging at 2200 RPM is as damaging as lugging at 1500 RPM. I have stalled my tractor dead a few times when my rotary cutter dug into the ground when mowing across some swells (and getting careless with position control). Those make me grimace.

Getut

 

[Bob_Skurka]

I don't know your particular engine, but I suspect that 2200 rpm is more than sufficient to keep your oil pressure up, and there would be zero worry of carbon clogging at that speed. I know on my tractors I do not have to run them at full throttle to get up to PTO speed, but PTO speed on my machines is much higher than 2200 rpms. However, I totally agree with you that running at PTO speed is louder than running at 2200. I'm surprised about your engine vibrations at faster speeds though, the engine should be running very smooth up near the top of the throttle range.

But as for the lugging, if you start lugging at 2200 and then make adjustments to stop the lugging you should have no problems, the concern would be if you continue to let it lug, if so, it will eventually bog down to the point where the engine speed slows, the oil isn't flowing the exhaust gasses are heating up and the carbon is going to start choking. Short terms of this are a non issue, but running like that will be an issue over time.

 

[getut]

Bob, I recant on the word vibration. It is more like a harmonic or something that rings throughout the tractor and me. I'm sure most everyone has experienced a vibration of just the right frequency that makes your knees get weak. PTO speed is very close to that frequency for me. The sound is also the difference between wearing earplugs and not wearing them. This next part is all in my head, I realize that.. but it just doesn't sound like those tractors in my childhood when its running flat out. I noticed this same thing on every tractor that I test drove. PTO speeds were way up there on engine speed. As long as my cutters cut at something lower, I will use the lower speed. My cutters (both rotary and finish mower), cut well down to 2000 engine RPM.

Getut

 

[rockyridgefarm]

I notice quiite a swing on the RPMs that manufacturers are setting their ratings at. Kubotas tend to be around 2700, the Deere's with Yanmars are 2600. while the new series from Deere is at 1500 rpm. Not suggesting that one is better than another, but it sure will seem that the Deere lugs down a lot better. I seem to remember that most older tractors were set in at lower rpms, too.

 

[slowrev]

Here is my totally unprofessional thought on this. I believe that lugging an engine designed for a higher RPM ( 3600 ? ) will do more damage than lugging an engine designed for lower RPM's ( 2000 ?). I have no real knowledge or facts to back this up, just seems to make sense to me. And no I did not stay at a Holiday Inn Exp last night.

Ben

 

[Dargo]

Obviously depending upon the specific engine, "lugging" as I refer to it would likely be running it under a load at RPM's under 1000 or 1200 or so. You are likely not going to lose working oil pressure in any good diesel engine unless you are under 1000 RPM. Of course that does vary per engine. Doing loader work or backhoe work etc. you should be able to run for decades at 1500 to 1800 RPM without any issue. You may need more RPM's to get the power you want, but unless you are lugging (lacking the power you need and needing to increase throttle) at those RPM's, you should be just peachy keen. /forums/images/graemlins/wink.gif

Besides, running the engine at speeds considerably over what you need wastes that liquid gold stuff we call diesel fuel! /forums/images/graemlins/cool.gif

 

[getut]

Thanks Dargo... that was exactly the information I was looking for to ease my mind.

I usually set my RPM to about 2300-2400 at no load, then take off. That setting at no load, yields about 2200 RPM under average mowing conditions and might drop to 2000 RPM while picking up forward momentum or going thru thick stuff. It still cuts good down to 2000 RPM while moving and can cut at even less RPM if going really slowly. I simply adjust HST peddle input to keep RPM no lower than 2000 RPM and that is the extent of my lugging.

The HST does pull the engine way down when just putt-putting around to get from one place to another. I typically throttle down to around 1700-1800 RPM and then travel in high range with the peddle fully depressed. This will typically pull the engine down to around 1400-1500 RPM. This yields a laid back travel speed and pleasant sound (like old time tractors). Makes it fun to be out there on it.

Getut

 

[Egon]

Yup - nothing like the good old stuff - just don't build them like they used too - think horses were a big factor one time.

Egon

 

[CTyler]

</font><font color="blue" class="small">( The HST does pull the engine way down when just putt-putting around to get from one place to another. I typically throttle down to around 1700-1800 RPM and then travel in high range with the peddle fully depressed. This will typically pull the engine down to around 1400-1500 RPM. This yields a laid back travel speed and pleasant sound (like old time tractors). Makes it fun to be out there on it.
)</font>

That pretty much what I do as well. Even doing loader work its' at 1800 in medium for the most part. If more oomph is needed rev it up a bit and back down again. About the only time it runs at 2600 is for mowing to get the right PTO and blade speed.

The only real lugging(idle - 1000rpm) is parking, driving it through the shop door to put it away or take it out.