What RPM is lugging ?

[RHestand]

I live in a rural area and I normally drive about 45 -55 MPH on these country roads.

On most of most of my trips around here I'm empty or light loads and flat terrain.

I have noticed that the lower the RPM I can pull the better the fuel mileage I get.

My question is do I use 6th gear at 1500 RPM or 5th at 1900RPM?

My mileage is better in 6th but am I lugging the engine?

How much torque am I making at 1500 RPM and how much does it take to get my 7500 LB. truck down the road under these conditions with no wind?

Thanks for any feedback on this.

RHestand

 

[JHardwick]

When I climb through the mountains, I donwshift under 2,000 with a load. Empty, you could probably drag it down a bit though. I like my Cummins hummin! I top many mountains at 3,000rpm in 5th!



The big trucks with flashers @ 45mph key up and say, DID YOU HEAR THAT DODGE Oo.



Note:I'm always loaded too!

 

[betterthanstock]

Empty, about 1350 on level ground is ok. 1200 is kind of marginal.

Heavy towing on the level, 1600-1700 is the low limit, 1800 or more uphill.



If you listen to it, it tells you by vibrations and so forth, when it doesn't like it.

 

[AKaiser]

Only way to know for sure is to put a pyro on it, as the biggest problem with lugging the engine is exhaust gas temperatures getting to the point of possible engine damage. When I was a kid, Dad had me working ground with an IH 3588 with a DT466. Told me to keep the RPMs over 2400 and EGTs below some figure that eludes me (15 plus years ago),and to downshift if EGTs went over the limit. Note, that was under full load. 2400 was the RPMs at rated HP. Chewed my tail really good one day when I told him I was running 2350. He's pretty particular about his machinery and maintenance, as was his Dad. We knew Grandpa was going senile (Alzh. ) when the equipment started to show wear from not being greased.

 

[JHardwick]

Funny thing is, my truck will be hotter, EGT wise, at 3,000 in 5th, than it will at 2,000 in 6th.

 

[Slow Six]

Mine is like JHardwick's I'll get higher EGTs at higher RPMs in fifth than I do at lower RPMs in sixth. I usuall don't downshift on heavy pulls untill about 16 to 1700 and if I'm close to the top I usaully get my foot out of it and just let it pull on up and as the hill flattens RPMs pickup. If I have to shift down I get out of it a bit to keep EGTs well into the safe zone. I've driven all my trucks this way and have never had a problem. Call me old school but I just hate to hear my engine screaming. I very rarely ever exceed 2500 RPM. Getting back to the original question, no I don't think you are lugging the engine. When you are driving like that if you push on the accelerator the engine will pick up RPMs, so it is not lugging.

 

[AKaiser]

You should get higher EGTs at 3000 RPMs, as you're getting close to the redline and burning more fuel. A diesel engine throws more fuel at the combustion chamber to keep the RPMs up if it gets bogged down under load. Since you're already at 3000 RPMs, it's burning more fuel than at 2000, especially if it's not lugging at 2000. Besides, 2000 RPM is 200 RPM or more over the beginning of max torque.

 

[JHardwick]

You should get higher EGTs at 3000 RPMs, as you're getting close to the redline and burning more fuel. A diesel engine throws more fuel at the combustion chamber to keep the RPMs up if it gets bogged down under load. Since you're already at 3000 RPMs, it's burning more fuel than at 2000, especially if it's not lugging at 2000. Besides, 2000 RPM is 200 RPM or more over the beginning of max torque.

The general rule of thumb around here has always been to downshift to lower EGTs ... ... ... the more air theory! It's never worked for me, although it seems to be accepted.

 

[klenger]

I drive around town empty below 1500 RPM fairly often, but will downshift if I need to accel more quickly. Note that I have the NV5600, which runs at lower RPMs in 6th.

 

[GCroyle]

I remember seeing something on the Cummins site that described lugging as a point at which the engine could not accelerate, no specifics, RPM, EGT or other.



I have no idea at what load or speed this happened but we installed a replacement trans in a 7. 3L 6speed (special situation) that had chipped the teeth on a gear from lugging (severly) and set up a major vibration in one gear only. We finally found out the "driver" did not like to shift while going through a series of lights and kept it in a higher gear and pulled through without downshifting.



Lugging with a load puts a clutch disc torsion damper into a heavy load on the springs of the damper, early failure is a possibility.

 

[DBond]

It looks like this has been a 6 speed thread, but I have recently had the same issue / question on my 48RE 4 speed. When I have m camper (3000 lb) and am on a winding road with a moderate grade I am often going 45-50 mph and about 1400 rpm. I can barley accelerate at that rpm and don't like the feel of it. If I'm up to 55mph around 1600 rpm it feels fine.

On the '05 I can't lock out OD, though I can downshift to 3rd with a ccle on the tow/haul button but that will shift back as soon as I let up on the throttle.

I wonder if my MPG is lower at the 1400 rpm area rather than having it in 3rd?

 

[AKaiser]

I remember seeing something on the Cummins site that described lugging as a point at which the engine could not accelerate, no specifics, RPM, EGT or other.

That's more or less correct, but an engine isn't lugging if it's at max RPMs, which is why I made the comment about rated engine speed. If you've got it in a gear and your RPMs are below the max, not increasing, AND you've got your foot to the floor, THEN you're lugging it. This is where torque rise comes into effect.



Read this tractor article from Tx A&M http://reveg-catalog.tamu.edu/16-Appendix.htm

 

[Pawpaw]

It looks like this has been a 6 speed thread, but I have recently had the same issue / question on my 48RE 4 speed. When I have m camper (3000 lb) and am on a winding road with a moderate grade I am often going 45-50 mph and about 1400 rpm. I can barley accelerate at that rpm and don't like the feel of it. If I'm up to 55mph around 1600 rpm it feels fine.

On the '05 I can't lock out OD, though I can downshift to 3rd with a ccle on the tow/haul button but that will shift back as soon as I let up on the throttle.

I wonder if my MPG is lower at the 1400 rpm area rather than having it in 3rd?

I thought the '05s would lock out OD if you hit the Tow/Haul button twice in rapid succession. I could be wrong though. Maybe that's an '06 feature.



Bob

 

[Forrest Nearing]

lugging in a stock truck is pretty much impossible... if you're at too low an RPM, the truck just won't go.



you start adding fuel to them and all that changes. on a solid flywheel you get all kinds of rattling through the driveline. they'll take a fair amount of abuse, but it isn't good for anything

 

[juicedcummins]

Lugging = foot on floor running below advertised peak torque rpm. [not possible with an auto]

 

[betterthanstock]

It looks like this has been a 6 speed thread, but I have recently had the same issue / question on my 48RE 4 speed. When I have m camper (3000 lb) and am on a winding road with a moderate grade I am often going 45-50 mph and about 1400 rpm. I can barley accelerate at that rpm and don't like the feel of it. If I'm up to 55mph around 1600 rpm it feels fine.

On the '05 I can't lock out OD, though I can downshift to 3rd with a ccle on the tow/haul button but that will shift back as soon as I let up on the throttle.

I wonder if my MPG is lower at the 1400 rpm area rather than having it in 3rd?

I drive a stickshift, but I thought if you place the shifter in 2nd, it will first go into 3rd (OD off). Try that. You can't break the transmission, it will only downshift when it's ready.

You are getting better mpg at 1400.