Leave engine running?

[rc51stierhoff]

In my simple understanding, idling does at least three things…1. Slowly warms up a cold engine (vs WFO immediately after start), 2. It helps cool an engine that has been hard working (keep in mind idling doesn’t get a diesel to operating temp…so in actuality they cool down a hard working diesel in controlled manner), 3. Waste fuel (some mistake running an idling diesel for running utilities/electric without running down the battery…battery most likely would not support all the current draw on some rigs)…if not doing to protect the dead battery / start, then it’s wasting fuel (no value added)

Basically if you need to leave it run, do so for a reason IMO, unless you like wasting fuel. For me (similar to what others above already mentioned) the simple rule is if getting off tractor for number 1 or to grab some other tool (yes, pun intended) 3-5ish minutes or less, let it run…if need to drop trau for some other seat time / number two, shut it down.

Letting a diesel idle that has emissions crap can be worse that shutting it off. Those are my simple thoughts.

 

[GeoHorn]

And what is that supposed to indicate?

Dan

Only that bearings …especially those sitting “in situ“ surrounding a crankshaft with oil passages that previously was pressurized…. remain oily for years when sitting. They don’t become “dry” as many folks imagine. The moment the crank rotates, the oil film is spread and the bearing is protected until oil pressure comes up again (likely about 20-30 secs.)

The most start-up wear occurs in the upper cylinders…but ring/cyl-wall fitment is so polished that even that is minor… And BTW…as regards long low idling speeds….. the underside of pistons (i.e. oil control ring distribution) and cyl walls get most lubrication from “sling” off the crankshaft. Long periods of low-speed idling results in low-levels of piston-ring/cyl-wall lubrication… Another reason to avoid long periods of idling.

But if it’s yours you get to do what you wish, of course.

 

[TheOldHokie]

That you will fall for almost anything you are told.

I guess you dont have a real answer.

Based on the original post I also suspect you have zero understanding of how a journal bearing works. Particularly what happens to the oil film when a crankshaft journal starts and stops rotating.

Dan

 

[TheOldHokie]

Only that bearings …especially those sitting “in situ“ surrounding a crankshaft with oil passages that previously was pressurized…. remain oily for years when sitting. They don’t become “dry” as many folks imagine. The moment the crank rotates, the oil film is spread and the bearing is protected until oil pressure comes up again (likely about 20-30 secs.)

The most start-up wear occurs in the upper cylinders…but ring/cyl-wall fitment is so polished that even that is minor… And BTW…as regards long low idling speeds….. the underside of pistons and cyl walls get most lubrication from “sling” off the crankshaft. Long periods of low-speed idling results in low-levels of piston-ring/cyl-wall lubrication… Another reason to avoid long periods of idling.

YMMV

A journal bearing must remain immersed in oil to function. The instant an engine starts spinning that residual oil film is swept away and lost due to shear. The bearing and journal surface are instantly in metal to metal sliding contact - or more technically a condition called the boundary lubrication regime by tribologists.

The several thousand PSI hydrodynamic oil film "wedge" that is needed to lift the journal off the bearing surface will not form until the oil pump delivers enough replacement oil to allow that same rotational shear to shape and maintain an area of high pressure differential. It is that localized hydrodynamic pressure differential that "floats" the journal and prevents metal to metal contact. The same thing happens in reverse when the engine shuts down. Thats why most journal bearing wear occurs at startup and shutdown.

You dont have to believe me. Go read any good (or for that matter bad) textbook on journal bearing theory and operation.

EDIT: The first picture is a little geeky. I added a second that might be easier to understand.

Dan

 

[The Evil Twin]

I fall squarely in the 5 minute camp. More than that, I don't see a need to run it. Especially if it has a exhaust filter. This applies to any ICE that I own.
Some exceptions are like fuelling up (except with the tractor). I let the vehicle run for that. Especially if I'm towing. Definitely don't want to heat soak the engine. It drives the wife bonkers that I do it. She gets all riled up if the MIL lights up because the gas cap is off

 

[P0234]

I leave it running, I always wanted to be a big rig driver but my family looked down on that. Same way I leave my car running while I get gas or anytime I'm around it. It makes me feel like I drive a big rig.

Sarcasm aside, no way do I leave it running, I don't want to breathe fumes while I'm around it. Whatever theoretical savings in wear aren't worth the health side effects. BTW has anyone actually worn out a Kubota engine, I mean like worn out, not from a lack of maintenance?

 

[skeets]

If its cold, I mean KULD out I will fire the old gal up go back in have a cup of coffee then come out and do what i need to do

 

[TheOldHokie]

Sarcasm aside, no way do I leave it running, I don't want to breathe fumes while I'm around it. Whatever theoretical savings in wear aren't worth the health side effects. BTW has anyone actually worn out a Kubota engine, I mean like worn out, not from a lack of maintenance?

I got one well on the way. Its taken me 25 years to get it to "weak" and in the unlikely event I live long enough it will probably be "toast" in another decade

Dan

 

[GrizBota]

A journal bearing must remain immersed in oil to function. The instant an engine starts spinning that residual oil film is swept away and lost due to shear. The bearing and journal surface are instantly in metal to metal sliding contact - or more technically a condition called the boundary lubrication regime by tribologists.

The several thousand PSI hydrodynamic oil film "wedge" that is needed to lift the journal off the bearing surface will not form until the oil pump delivers enough replacement oil to allow that same rotational shear to shape and maintain an area of high pressure differential. It is that localized hydrodynamic pressure differential that "floats" the journal and prevents metal to metal contact. The same thing happens in reverse when the engine shuts down. Thats why most journal bearing wear occurs at startup and shutdown.

You dont have to believe me. Go read any good (or for that matter bad) textbook on journal bearing theory and operation.

EDIT: The first picture is a little geeky. I added a second that might be easier to understand.

Dan

View attachment 116215

View attachment 116219

Nice explanation. So when h min (the thickness of the squeeze film) is less than the roughness of the surface (e.g. height of the asperities) then the bearing journal and the bearing surface are in at least intermittent contact with one another for some portion of the surface area between the journal and bearing.

 

[DustyRusty]

Nice explanation. So when h min (the thickness of the squeeze film) is less than the roughness of the surface (e.g. height of the asperities) then the bearing journal and the bearing surface are in at least intermittent contact with one another for some portion of the surface area between the journal and bearing.

 

[GrizBota]

You’ll have to think. Look at the @TheOldHokie post #24 above and read below, about boundary lubrication.

Boundary Lubrication

or post cute memes.

 

[Russell King]

And later you can try to wrap your head around the Babbitt bearing in combination with the lubrication regimes of bearings

Babbitt (alloy) - Wikipedia

en.wikipedia.org

Sleeve Bearing Lubrication

Plain Bearings There are two broad types of bearings used in machinery today: plain and rolling element bearings. This article targets the special lubrication requirements of plain bearings,...

www.machinerylubrication.com

good times for the mechanical and fluid engineers!

 

[TheOldHokie]

Nice explanation. So when h min (the thickness of the squeeze film) is less than the roughness of the surface (e.g. height of the asperities) then the bearing journal and the bearing surface are in at least intermittent contact with one another for some portion of the surface area between the journal and bearing.

I dont think any of this is news to you

That condition is called the mixed mode regime. In a journal bearIng you want to maintain a full hydrodynamic regime where HMIN is never less than the height of the asperities and there is no metal to metal contact.

HMIN is largely dependent on the radial loading on the journal, the rotational surface speed of the journal relative to the bearing, diametral bearing oil clearance, and the dynamic viscosity of the oil.

Slow engine down HMIN decreases and you get boundary conditions

Thin oil out with heat or loss due to hydrodynamic shear force HMIN decreases.and you get boundary conditions.

Lug (load) engine up at low RPM HMIN decreases and you get boundary condtions.

And the nail in the coffin. Over tine bearing clearances inevitably increase with wear, HMIN decreases during nornal operation, boundary and mixed mode lubrication begins to occur more frequently, and the rate of bearing wear accelerates.

Dan

 

[GeoHorn]

A journal bearing must remain immersed in oil to function. The instant an engine starts spinning that residual oil film is swept away and lost due to shear. The bearing and journal surface are instantly in metal to metal sliding contact - or more technically a condition called the boundary lubrication regime by tribologists.
…

“Instant”….is a fairly short period of time. …. and That is the part of the old wive tales that is Horth-thit.

If that were as true as the rumor-mills promote … then None of these machines would last a month. Why? Because the bearings are not “dry” …despite the rampant imaginations.

They were assembled at the factory with lubrication and they’ve been wet with lubrication ever since as long as they’ve not sat longer than many months without starting.

Like I said previously… “You will never wear one of these out by starting it.”

My 9N Ford made betweeh 1939 and ‘42 had it’s bearings (conn-rod only) replaced ONE TIME in 1999 and that was only because the thing was partially disassembled due to a fractured cylinder sleeve. The main bearings were never removed. It sat for many winter months at a time during the 20-year period I owned it ….and While there is no way to know how many times that thing was started…. Starting it did not kill it. It’s likely still doing work to this day for it’s “new” owner over in Looeasyana since it was sold in 2018.

 

[WFM]

This is a surprising thread. I always thought I was hurting my engine by starting and stopping it so frequently.
If I have a couple cord of wood to stack from a pile I'll use the bucket scoop up a bucket full(shut down)straighten out some sticks toss on some more by hand(Start up) drive to the pile(shut down) I'm driving like 50'. Repeatedly stacking.
Another reason I change my oil/filter more often is my starting stopping.

 

[GeoHorn]

This is a surprising thread. I always thought I was hurting my engine by starting and stopping it so frequently.
If I have a couple cord of wood to stack from a pile I'll use the bucket scoop up a bucket full(shut down)straighten out some sticks toss on some more by hand(Start up) drive to the pile(shut down) I'm driving like 50'. Repeatedly stacking.
Another reason I change my oil/filter more often is my starting stopping.

Well,…if it’s as I’m imagining your wood-stacking operations… I’d not unnecessarily shut down while I rearranged wood in the bucket…or unloaded it… as long as I was only taking a few minutes each time.… Mostly for convenience, but also to avoid working on an unpowered, possibly sinking bucket while it was still in the air. I wouldn’t consider that as unnecessary idling, personally.
If it was a task I was “dragging out” over a long period I’d probably lower the bucket onto something steady (like the ground perhaps) to do that task.

(I’m now tired of this subject …so I’m moving on to other things in case anyone wants to fearlessly attack my opinion on it.)

 

[TheOldHokie]

“Instant”….is a fairly short period of time. …. and That is the part of the old wive tales that is Horth-thit.

If that were as true as the rumor-mills promote … then None of these machines would last a month. Why? Because the bearings are not “dry” …despite the rampant imaginations.

They were assembled at the factory with lubrication and they’ve been wet with lubrication ever since as long as they’ve not sat longer than many months without starting.

Like I said previously… “You will never wear one of these out by starting it.”

Ah yes - the engineers and tribologists are all lying to us.

Apparently you cant (actually wont) accept the well understood physics of journal bearing operation. Go down to the library and pick up a copy of Shigley's Fundamentals Of Modern Mechanical Engineering and read the section on lubrication, particularly journal bearings as opposed to rolling element bearings. You can skip the nasty calculus - you dont need to understand it to understsnd the basic operation. Its the same phenomenon that provides the lift to the airfoils (wings) on your airplanes. Its explained by the same set of Navier-Stokes equations that aerospace engineers use when they design airfoils. Lubrication engineers use those same equations when they design journal bearings. In both cases when you loose lift the supported element falls to the ground and bad things can and do happen.

Journal bearing lubrication has been studied, modeled, and measured to death. The results are clear. Start/stop cycles are the primary source of the breakdown in lubrication that causes wear.

But you are not going to read or research anything. You are going to ignore/dismiss the science I put forward rather than try to understand it. It does not align with your preconceived beliefs and hence its all "Horth-hit".

Dan

 

[GreensvilleJay]

My first tractor, Allis-Chalmers D14,sat in an open lean-to for 25+ years(so long top 1/4 of diff gears were rusty..),once I 'unstuck it',tossed gas into the carb,12v to starter and it ran THEN I did a proper oil change.She's run like a Swiss clock since then (23 years now).
Scientists and their math aside, once you get ANY oil where it's supposed to be, things work. With today's 'modern, new ,improved oils' stuff should work even better.
I'm waiting for them to announce we need to run -30W60 in engines now......

 

[The Evil Twin]

Just you wait until the EPA mandates stop/ start in our tractors. My commuter car does that and I hate it!

 

[GreensvilleJay]

that play heck for the cops around here, 3 sat, engines idling for just over 10 hrs, waiting to catch a bad guy....